Chapter 2

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Principles of Green Concrete Natt Makul Building Technology Program, Faculty of Industrial Technology, Phranakhon Rajabhat University, 9 Changwattane Road, Anusaowari, Bang Khen, Bangkok 10220, Thailand. E-mail address: [email protected] (Natt Makul).

1.1 Introduction Climate change, signified principally by global warming, is a critical global issue given that it has the potential to jeopardize all human society. Among many causes, the construction industry is responsible for a major portion of greenhouse gas emissions. For example, the process through which cement is produced yields approximately 7% of total CO2 emissions worldwide (Kim et al., 2013). With increasing interest in sustainable development on the part of the public, industry, and government, environmental assessment in construction is becoming more important. Society and the social changes that have occurred worldwide have brought a high demand to bear on the construction industry in terms of the world’s material and energy resources. As it consumes considerable resources and, therefore, has a significant impact on the environment, the construction industry must address certain consequential issues in the effort to achieve sustainable development (Edvardsen & Tølløse, 2001). With the exception of water, concrete is the most widely used material on earth, with nearly three tons used annually for each man, woman, and child (PCA, 2015). In addition, the use of concrete is evolving. Modern concrete is more than simply a mixture of cement, water, and aggregates. Instead, modern concrete is more likely to contain mineral components, chemical admixtures, fibers, etc., than earlier concrete and to use these in larger quantities than was previously the case. The

2 development of these smart concretes resulted from the emergence of a new science of concrete, a new science of admixtures, and the use of sophisticated scientific apparatus to observe the microstructure and even the nanostructure of concrete (Aïtcin, P-C., 2000). Sustainable industrial growth will influence the cement and concrete industry in many respects. One important issue is the use of environmentally friendly (―green‖) concrete to enable worldwide infrastructure growth without incurring an increase in CO2 emissions (Edvardsen & Tølløse, 2001). Concrete for the environment is defined as sustainable development through the planned management of a natural resource or of the entire environment of a particular ecosystem in order to prevent exploitation, pollution, destruction, or neglect and to ensure the future use of the resource. Sustainable development has been defined as development that meets the needs of the present without compromising the ability of future generations to meet their needs (fib, 2012). To support the global consensus in favor of sustainable development, technical strategies for ensuring the sustainability of concrete construction have been presented, which suggest saving materials in building design, maximizing the durability of concrete, using waste or supplementary cementitious materials (e.g., fly ash and slag), and recycling concrete (Kim et al., 2013). Finally, the concrete of tomorrow will be green. Concrete will have to evolve with reference to the environment within a sustainable development perspective, which means that more mineral components will be blended with clinker and waterbinder material ratios will be lowered in order to increase the lifecycle of concrete structures and to increase to the maximum extent the use of hydraulic binders and aggregates (Aïtcin, P-C., 2000).

1.2 Concrete as a green material: A sustainable development point of view Concrete is by far the most widely used construction material worldwide. Its huge popularity is the result of a number of well-known advantages, such as its low cost, general availability, and wide applicability. But the popularity of concrete comes at a great cost to the environment. The billions

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of tons of natural materials mined and processed each year, by their sheer volume, are bound to leave a substantial mark on the environment (Table 1.1). Most damaging are the enormous amounts of energy required to produce Portland cement as well as the large quantities of CO2 released into the atmosphere in the process. Table 1.1 The Environmental Costs of Concrete (Meyer, C., 2005). Key impact Impact on the environment Worldwide Over ten billion tons of concrete are produced each year. In the United States, the annual production of over 500 million tons translates to about two tons for each man, woman, and child. Such volumes require vast amounts of natural resources for aggregate and cement production. CO2 The production of one ton of Portland cement causes the release of one ton of CO2 into the atmosphere. CO2 is a greenhouse gas that contributes to global warming, and the cement industry alone generates about 7% of it. Energy-intensive North American plants have improved their energyefficiency considerably in recent decades to the point where this is now comparable to that of plants in Japan and Germany. It is technically next to impossible to increase that energy-efficiency much further below the current requirement of about 4 GJ per ton. Environment The demolition and disposal of concrete structures, pavements, etc., constitutes another environmental burden. Construction debris accounts for a large fraction of our solid waste disposal problem, and concrete constitutes the largest single component of this debris. Water requireThe water requirements are enormous and particularly ments burdensome in regions of the world that are not blessed with an abundance of fresh water. The concrete industry uses over 1 trillion gallons of water each year worldwide, and this does not include wash water or curing water.

4 Because of limited natural resources, concern over greenhouse gases (GHGs), or, both, cement production is being curtailed, or at least it is not being increased in order to keep up with the population increase in some regions of the world. It is, therefore, necessary to look for sustainable solutions for future concrete construction. A sustainable concrete structure is constructed to ensure that the total environmental impact during its lifecycle, including its use, will be minimal. Sustainable concrete should have a very low inherent energy requirement, be produced with little waste, be made from some of the most plentiful resources on earth, produce durable structures, have a very high thermal mass, and be made with recycled materials. Sustainable constructions have a small impact on the environment. They use green materials, which have low energy costs, high durability, low maintenance requirements, and contain a large proportion of recycled and/or recyclable materials. Green materials also use less energy and fewer resources than do non-green materials and can be used to produce high-performance cement and concrete. Concrete must keep evolving to satisfy the increasing demands of its users. Therefore, designing for sustainability means accounting for the short-term and longterm environmental consequences in regard to every aspect of design (Naik, T.R., 2008). Traditionally, the design of concrete structures has concentrated on the construction phase, optimizing construction costs and short-term performance. The notion of sustainable development raises the issue of a strong need for an integrated lifecycle design such that all phases during the entire service life of the structure are considered, as shown in Fig. 1.1. It is a fact that concrete structures exposed to an aggressive environment require extensive maintenance and repair work. The environmental loads associated with the maintenance and repairs needed by structures in such conditions very often dominate sources the entire service life of the structures (Edvardsen & Tølløse, 2001). As the service life of a concrete structure is often 50–100 years, a lot of people can be expected to use such structures and play a part in their repair and maintenance throughout their lifecycle (fib, 2012). There are multiple aspects to the design and production of concrete structures as follows:

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 Design – The design is established as a cooperative venture between the building owner and the consultant. The design should be in accordance with relevant specifications, rules, and legislation. The time scale is months.

Fig. 1.1 Phases in the lifecycle of a concrete structure to considered in the lifecycle inventory (Edvardsen & Tølløse, 2001).  Construction – The construction is mainly governed by the material suppliers and the contractors. The design specifications act as minimum requirements. Sometimes, the contractor overrules the design if an alternative solution is more suitable. During this phase, the time schedule is often tight, which may negatively influence the environmental footprint of the structure. The time scale is months.  Operation and use of the structure – During the service life of a structure, the building owner and the end-user are responsible for its operation and maintenance. If the initial design is successful, the construction will function for decades without any need for major repairs or alterations. The time scale is decades.

6  Maintenance – Most often, buildings and structures need maintenance and modifications after about 30 years because during the pre-construction phase it is not generally possible to foresee necessary changes. However, the design phase is important in order to obtain sound low-maintenance and durable solutions. This phase involves choosing appropriate materials and design details and also executing the design. The time scale is decades.  Demolition, reuse, and recycling – At the end of its service life, a structure is most likely to be demolished and recycled to a certain degree. In cases in which structures included built-in harmful substances allowed at the time of construction but later banned, recycling may be restricted significantly. However, even though it is very difficult to foresee future changes during the pre-construction phase, this effort should still be attempted in order to cover the potential reuse and recycling of materials used in construction with contemporary state-of-the-art technology. The National Ready Mixed Concrete Association (NRMCA, 2009a) presents a vision for sustainability initiatives according to which the concrete industry is seen as uniquely positioned to meet the challenges of sustainable development. The NMRCA sees the industry as capable of creating products that help improve the overall footprint of the built environment. To fully realize this vision, the concrete industry must approach sustainable development through the lifecycle perspective. The lifecycle phases of concrete include material acquisition, production, construction, use (operations and maintenance), and recycling. The industry evaluates and will continue to evaluate all phases of its product lifecycle in order to reduce its environmental footprint. Further, the industry will continue to evaluate each phase of the lifecycle to employ strategies for reducing its environmental impact (Table 1.2). The concrete industry is dedicated to continually improving through developing its products and processes. The industry continues to increase its use of recycled materials, including industrial byproducts, thus conserving valuable natural resources and reducing the energy required to manufacture concrete. The industry continues to explore new ways to further reduce its

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carbon footprint through the development of innovative cements and concrete mixtures. Concrete companies also strive to improve manufacturing processes, including the use of alternative energy sources, to minimize the energy used in production and associated greenhouse gas emissions. Finally, the industry continues to enhance transportation efficiency and delivery methods to reduce the environmental impact of the construction process.

Table 1.2 Strategies for Reducing the Environmental Impact at Each Phase of the Lifecycle of Concrete.

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This chapter outlines goals for reducing the overall environmental footprint of concrete construction and provides strategies for achieving these goals. The concrete industry has been a key contributor in building this nation’s infrastructure and will continue to enhance the sustainability of our built environment for generations to come (NRMCA, 2009a). The principles of Sustainable Development and Green Buildings have penetrated the construction industry at an accelerating rate in recent years. Yet, despite making significant improvements in terms of sustainability, as discussed, the concrete industry has an enormous environmental footprint and, therefore, has a long way to go in terms of becoming greener and of shedding its negative image. The idea of using recycled materials in concrete production was widely unknown only a few years ago, yet concrete producers now know that they need to change. The goals in regard to becoming more environmentally friendly in terms of producing concrete can be summarized as follows: (1) replace as much Portland cement as possible with supplementary cementitious materials (SCM), especially those that are by-products of industrial processes, such as fly ash, ground granulated blast furnace slag, and silica fume; (2) use recycled materials in place of natural resources; (3) improve the durability and service life of structures, thereby reducing the amount of materials needed for their replacement; (4) improve concrete’s mechanical and other properties, which can also reduce the amount of materials needed; (5) reuse wash water (Meyer, C., 2009). Various strategies have been followed, separately or in combination, to improve the sustainability of concrete and even to develop green or ecological concrete. These strategies consist of incorporating recycled materials into concrete, optimizing the mix design, reducing CO2 emissions by decreasing the Portland cement content, partially replacing Portland cement with cementitious by-product materials, increasing the durability of concrete in order to extend its service life and to reduce long-term consumption of resources, and selecting low-impact construction methods (Long et al., 2015). Basically, an environmentally green concrete structure is one in which all these issues have been considered and addressed effectively in the design and construction phase and during operation and maintenance likewise. This is achieved by drawing on the inherent environmentally

10 friendly properties of concrete. The concrete structure should be designed and produced so that it meets the needs of end-users; i.e., the right concrete is chosen for any given application (fib, 2012). A sustainable concrete structure is one that is constructed so that the total negative societal impact during its entire lifecycle is minimal. Designing with sustainability in mind includes accounting for the short- and long-term consequences of the structure. To decrease the long-term impact of structures, maximizing durability is paramount (Naik, T.R., 2008). In summary, green concrete is defined as a concrete that uses waste material as at least one of its components and/or its production process does not lead to environmental destruction. Further, to be considered green, concrete must also have high performance and lifecycle sustainability. In other words, green concrete is an environmentally friendly material. Green concrete represents a significant improvement over traditional concrete in regard to the three pillars of sustainability: environmental, economic, and social impact. The key factors used to determine whether concrete is green are the percentage of materials used to replace Portland cement, the manufacturing process and methods used, and the performance and lifecycle sustainability impact. Green concrete should be produced in accord with reduce, reuse, and recycle techniques or any two of these processes in terms of the concrete technology use. The three major objectives governing the green concept in concrete are to reduce greenhouse gas emissions (i.e., carbon dioxide emissions) from the cement industry; to reduce the use of natural resources such as limestone, shale, clay, natural river sand, and natural rocks that are being consumed and cannot be returned to the earth; and the use of waste materials in concrete, which results in air, land, and water pollution. The objective underlying the production of green concrete is to effect sustainable development—i.e., development that takes place without destroying natural resources (Suhendro, B., 2014).

1.3 Guidelines for green concrete Water, sand, stone, gravel, and other ingredients make up about 90% of traditional concrete mixture by weight. The processes of mining sand and

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gravel, crushing stone, combining the materials in a concrete plant and transporting concrete to the construction site require very little energy and, therefore, result in the emission of a relatively small amount of CO 2 into the atmosphere. The amounts of CO2 produced by concrete are primarily a function of the cement content in the mix designs. It is important to note that structures are built with concrete and not cement. Depending on its performance requirements, concrete uses about 7% or 15% cement by weight. The average quantity of cement is around 250 kg/m3. One cubic meter of concrete weighs approximately 2400 kg. As a result, approximately 100 to 300 kg of CO2 is emitted for every cubic meter of concrete produced or approximately 5 to 13% of the weight of the concrete produced, depending on the mix design. A significant portion of the CO2 produced during the manufacture of cement is reabsorbed into the concrete during the product lifecycle through a process called carbonation. According to NRMCA (2012) estimates, between 33% and 57% of the CO2 emitted from calcination is reabsorbed through carbonation of concrete surfaces over a 100-year lifecycle. The global cement industry accounts for approximately 5% of global CO2 emissions. Therefore, whichever way one looks at the issue of CO2 emission, the production of concrete accounts for a very small percentage of overall CO2 emissions. This is not to say that progress should not be made in reducing the CO2 emissions from concrete as produced. However, reductions in CO2 emissions reductions in the production of concrete have the potential to account for at best a 2% reduction in the emission of CO2 globally. Obla (2009a, 2009b) summarizes this point of view in What is Green Concrete? as follows: 1) CO2 emissions from 1 ton of concrete produced vary from between 0.05 to 0.13 tons. In total, 95% of all CO2 emissions from a cubic yard of concrete are from cement manufacturing. It is important to reduce CO2 emissions through the greater use of SCM. 2) It is important not to focus solely on CO2 emissions from cement and concrete production. Doing so limits the total global CO2 reduction possible to at best 2%. Keeping a holistic cradle to cradle perspective and using life cycle assessment (LCA) can help reduce CO2 by a much greater amount, as there is evidence to show that most of the energy is consumed during the operational phase of the

12 structure (heating and cooling). Concrete is very effective in reducing energy consumption due to its high solar reflectivity and high thermal mass among other benefits. 3) Focusing solely on CO2 emissions from cement and concrete production increases the perception that concrete is not sustainable. This is inaccurate, as operationally concrete has substantial sustainability benefits. An incorrect perception can lead to a less sustainable material choice. 4) Focusing solely on CO2 emissions from cement and concrete production does not encourage the use of recycled or crushed returned concrete aggregates; use of water from ready-mixed concrete operations; use of sustainable practices such as energy savings at ready-mixed concrete plants; and use of sustainable transport practices. This is because only 5% of CO2 emissions from a cubic yard of concrete is due to the use of virgin aggregates, water, plant operations, and material transport to the plant. 5) The removal of prescriptive specification restrictions and a focus on performance and the use of incentives is an effective way to encourage the production of sustainable concrete with a low CO2 emission. An essential step toward achieving sustainable development of concrete was taken with the establishment of a large Danish research project called Resource Saving Concrete Structures (colloquially Green Concrete), which ran from 1998 to 2001. The project involved partners from all sectors related to concrete production, i.e., cement and aggregate producers, a contractor, a ready-mix plant, a consultant, building owners, the Danish Technological Institute, and two technical universities. The purpose of the project was to study holistic approaches to the production of concrete whereby considerations pertaining to material characteristics and to structural performance would be integrated into the following tasks (Table 1.3):  To develop green cement and green concrete types, e.g., concrete in which the percentage of cement is decreased considerably because high amounts of cement replacement materials are used instead. Such replacement materials include fly ash, silica fume, other natural pozzolans, and waste materials such as stone dust, crushed concrete,

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concrete slurry, cement stabilized foundations with waste incineration and other inorganic residual products.  To develop green design strategies, which require less maintenance and repair work, using, for example, stainless steel instead of black reinforcement. This is of particular interest, as it is well known that in concrete structures located in aggressive environments the highest environmental loads result from maintenance and repair work during the service life of the structure.  To develop green structural designs and structural solutions for green concrete, e.g., optimized structural detailing by minimizing the structural dimensions using high performance concrete. Table 1.3 Combination of Traditional and Green Concrete/Concrete Structures (Edvardsen & Tølløse, 2001). Traditional structure Green concrete Traditional structure

Restricted amount of fly ash and microsilica

Green concrete

Cladding with stainless steel Stainless steel reinforcement

High amount of fly ash and microsilica Green types of cement Use of stone dust, slurry, waste incineration Green concrete (see above) plus stainless steel cladding or stainless steel reinforcement

Proske et al. (2013) presented a step-by-step approach implemented in order to develop eco-friendly concretes with reduced cement and water content. In parallel, several experimental attempts were made to evaluate the required concrete performance for practical purposes. According to the results, the following conclusions can be derived: 1) CO2 emissions can be reduced significantly in structural concretes. A significant reduction in Portland cement demand can be achieved by using high-performance superplasticizer, high-strength cement, and optimized particle-size distribution.

14 2) The replacement of Portland cement and water with mineral fillers, such as limestone powder, provides an optimal paste volume in a low-water mixture. It was shown that concretes with cement clinker and slag contents as low as 150 kg/m3 can meet the usual requirements for workability, compressive strength (approx. 40 N/mm2), and other mechanical properties. 3) The carbonation depth of eco-friendly concretes with at least 175 kg/m3 clinker and slag were observed to be lower than that of conventional concretes for exterior structures. 4) A reduction in the global-warming potential of up to 35% compared with that of conventional concrete can be seen as well as a reduction of more than 60% when granulated blast-furnace slag is used. An allocation of slag of this magnitude, however, would decrease the extent to which the concrete’s global-warming potential could be decreased. 5) Practical applications were verified in precast and ready-mixed concrete plants. The results showed that eco-friendly concretes in both fresh and hardened states are of an acceptable standard for use in the aforementioned industries. The use of concrete can facilitate the process of obtaining Leadership in Energy and Environmental Design (LEED) Green Building certification. LEED is a point rating system devised by the U.S. Green Building Council (USGBC) to evaluate the environmental performance of buildings and to encourage market transformation toward sustainable design, as shown in Table 1.4. The system is credit-based, allowing projects to earn points for environmentally friendly actions taken during the construction and use of a building. LEED was launched in an effort to develop a consensus-based, market-driven rating system to accelerate the development and implementation of green building practices (PCA, 2005).

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Table 1.4 Five Properties of Concrete that Contribute to the Construction of Greener Buildings. No. Main categories 1 Concrete creates sustainable sites 2 Concrete enhances energy performance 3 Concrete contains recycled materials 4 Concrete is manufactured locally 5 Concrete builds durable structures

Concrete is a key element in green buildings and when used effectively can play an important role in obtaining a LEED certification. For illustrative purposes, the advantages of concrete for efforts to obtain LEED 2015 certification are considered in detail in this section. LEED has become one of the most standard widespread and well-known certifications for rating green practices in construction worldwide. LEED uses a system of points to determine which of its various certifications to award any given project. Platinum level is the most rigorous and marks industry best practices with 80 or more points. Gold level requires 60 points, Silver needs 50 points, and the minimum level of certification is achieved with 40 points, as shown in Table 1.5 (Blanco-Carrasco et al., 2010). Table 1.5 LEED Certifications and Points Required for Each Level. LEED Certification Levels Points Required Certified 40–49 Silver 50–59 Gold 60–79 Platinum 80+

To ensure the future competitiveness of concrete as a building material, it is essential to improve the sustainability of concrete structures. Great potential for reducing the environmental impact and consumption of scarce resources has been identified in the field of concrete construction, especially in the production of raw materials, concrete technology, and structures. For

16 concrete that is developed, produced, and used in an environmentally friendly way the term ―green concrete‖ is commonly used. Based on experimental results, a step-by-step procedure for the development of low-carbon concretes with efficient use of reactive materials has been devised by Proske et al. (2014), who recommend the following key steps: 1) Selection of cement of a high-strength class and composed of ecofriendly constituents such as limestone, granulated blast-furnace slag (GBFS) or fly ash. 2) Optimization of water content and cementitious material in the concrete paste. 3) Optimization of the paste volume. Glavind et al. (1999) presented three development projects through which the researchers produced and studied green concrete in three ways: 1) To minimize the clinker content, i.e., by replacing cement with fly ash, microsilica in larger amounts than are allowed today, or by using extended cement, i.e., Portland limestone cement. The preliminary plan is to analyze concrete for the passive environmental class with fly ash amounts of up to 60% of the total amount of cement and fly ash, concrete with Portland limestone cement for the aggressive environmental class, and concrete with dry desulphurization products for the passive environmental class. 2) To develop new green cements and binding materials, i.e., by increasing the use of alternative raw materials and alternative fuels, and by developing/improving cement with low energy consumption, a new, rapid hardening low-energy cement based on mineralized clinker is currently ready for testing. 3) Concrete with inorganic residual products (stone dust, crushed concrete as aggregate in quantities and for areas that are not allowed today) and a cement-stabilized foundation with waste incinerator slag, low-quality fly ash, and/or other inorganic residual products. Currently, an information screening of potential inorganic residual products is being carried out. The products are described by origin, amount, particle size and geometry, chemical composition, and possible environmental impact.

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The main goal of producing green concrete is to reduce the harmful residuals generated across industry and to produce concrete in a way that is more economical than are the standard processes currently in use, as shown in Table 1.6. To enable concrete of this nature to be produced in this way, new technology is under development. The technology is designed to account for all phases of a concrete construction’s lifecycle, i.e., structural design, specification, and manufacturing and maintenance. Further, the technology applies to all aspects of performance, i.e., mechanical properties (strength, shrinkage, creep, static behavior, etc.), fire resistance (spalling, heat transfer, etc.), workmanship (workability, strength development, curing, etc.), durability (corrosion protection, frost, new deterioration mechanisms, etc.), and environmental aspects (CO2 emission, energy use, recycling, etc.) Tafheem et al., 2011. The knowledge and experience in Denmark pertaining to how to produce concrete with a reduced environmental impact can be divided into two areas, concrete mix design and cement and concrete production, as shown in Table 1.7: Table 1.6 Goals of Producing Green Concrete. Goals related to residual Environmental Goals reduction and economy • Concrete with minimal clinker • CO2 emission caused by concrete content production must be reduced by at • Concrete with green types of least 30% cement and binders • The concrete industry’s own • Concrete with inorganic residual residual products must be used in products concrete production • Operation and maintenance • New types of residual products, technology for green concrete previously landfilled or disposed structures of in other ways, must be used in • Green structural solutions and concrete production structural solutions for green con- • CO2-neutral, waste-derived fuels crete must replace at least 10% of the fossil fuels in cement production

18 Table 1.7 How to Produce Concrete with Lower Environmental Impact (Glavind et al., 1999). Key factor How to produce concrete Concrete mix design: - use cement with a reduced environmental impact - minimize cement content - substitute cement with pozzolanic materials such as fly ash and microsilica - recycle aggregates - recycle water Cement and concrete production: - engage in environmental management

The basic principles of green concrete mix design are introduced and a systematic study of the influence of the cement content on the fresh and hardened properties of concrete as well as on its durability parameters are presented in Müllera et al. (2014). From the results, it can be seen that green concretes are highly sustainable and, depending on the attack scenario, might be sufficiently durable when subjected to exposure associated with corrosion. The key challenge in the development of concretes with minimum environmental impact lies in maintaining sufficient workability at a very low water content. As in the fresh state, water is needed to fill the inter-granular voids in the mix, which consist of aggregates and cement particles. Further, water is needed to lubricate the deformation of this granular system, as a reduction in water content at a constant packing density would inevitably result in a loss of workability and in the formation of voids. Against this background, methods for optimizing the packing density of the granular mix constituents constitute a key step in the mix development process. The mix development algorithm applied in this study (Müllera et al., 2014) is detailed in Fig. 1.2

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Fig. 1.2 Schematic sequence of the mixture development procedure for green concrete (Müllera et al., 2014).

Many concrete programs in industry have a perspective on the broader issue of green technology and environmental performance. Here, the desirable qualifications of green concrete for sustainability are listed (Lu, 2012): 1) Long service life and high performance. Reinforced concrete’s durability ensures that the structure will retain its structural capabilities for many years due to the high-performance concrete, e.g., anticorrosion and anti-cracking concrete. The carbon footprint and high energy consumption of the cement industry are minimized when it is not necessary to replace or repair a concrete structure. 2) Maximized recycling materials usage and minimized environmental impact. Concrete producers can replace significant amounts of cement in their mixtures with industrial by-products such as silica fume and blast-furnace slag. The use of these materials in concrete prevents them from entering landfills and minimizes cement consumption, even producing a more durable concrete. Waste industry products can be recycled and, in turn, result in less waste being released into the environment.

20 3) Minimized transportation cost. Producers of concrete should take advantage of local materials, as reinforced concrete components can be made locally anywhere in the world. This turns out to be the key element in reducing emissions due to transportation. Through the use of local materials, the impact of transportation and energy consumption can be minimized. In determining the suitability of green concrete for any given structure (Garg and Jain, 2014), several factors in favor of green concrete should be considered: The use of green concrete reduces the dead weight of a structure and reduces crane age load; allows handling, given greater lifting flexibility with lighter weight; affords good thermal and fire resistance and better sound insulation than traditional granite rock does; improves the damping resistance of buildings; speeds up construction; reduces the concrete industry’s CO2 emissions by 30%; increases the concrete industry’s use of waste products by 20%; produces no environmental pollution and supports sustainable development; requires less maintenance and repairs and sometimes gives better workability than conventional concrete does; yields better compressive strength behavior when its water/cement ratio is more than that of conventional concrete; and offers flexural strength almost equal to that of conventional concrete. A comprehensive list of green concrete technologies is given in Table 1.8 (fib, 2012). Jin and Chen (2013) summarize the potential barriers to using green concrete. Despite the potential benefits of using green raw materials in concrete production, barriers exist in regard to the properties of the concrete produced, its cost-effectiveness, and industry perceptions: 1) Concrete properties: Using waste streams as concrete ingredients could improve certain types of concrete properties while undermining some others. 2) Cost-effectiveness: Cost-effectiveness would be the driving force for the industry to implement green concrete. Recycling and reuse of waste materials require extra labor and energy input. 3) Industry perception/practice: The construction and building product industry is conservative in nature due to the fear of product failure.

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Table 1.8 Comprehensive List of Green Concrete Technologies (fib, 2012). Key topics Green concrete technologies 1. Choice of raw materials The production and use of blended cements have a long and successful tradition. Today, about 70% of the cement produced and used in Europe have several main constituents. The use of other main constituents along with Portland cement clinker will depend on the availability and quality of these materials at an affordable cost. A number of supplementary cementitious materials (SCM) are used to blend either the cement or the concrete. These materials are used as a supplement to the clinker content. In most cases, they allow the clinker or cement content to be reduced, and in some cases specific concrete properties are improved. The most commonly used SCMs are: - Fly ash from coal-fired power plants - Silica fume - Blast furnace slag - Sewage sludge - Rice husk ash - Recycled ground glass - Limestone powder - Metakaolin - Natural pozzolan The choice of aggregate is very much a local decision. Natural sand and gravel resources are being depleted in some regions and countries, and the trend is toward using more crushed and manufactured aggregates.

22 Table 1.8 (Cont.) Comprehensive List of Green Concrete Technologies (fib, 2012). Key topics Green concrete technologies 1. Optimization of the mix One way for a concrete producer to optidesign with respect to mize the mix design and minimize clinker clinker content consumption is to use cement with several main constituents. Another way is to mix pure Portland cement with other mineral additions. A concrete producer who is adding new materials to a mix design must demonstrate that these materials do not cause problems in regard to the concrete’s performance. It may be that supplementary cementitious materials (SCM) can be used to replace cement or perhaps aggregates. 3. Production method The concrete industry is a large consumer of water. The water demand for concrete mixing depends on the mix design and the use of plasticizing additives. However, concrete plants also consume a relatively large amount of water for washing the mixer, conveyor belts, formwork, trucks, and laboratory equipment. It is noted that recycling saves money for the producer in terms of a significantly reduced need for fresh water and obviating the need for a chemical treatment plant. Moreover, noise and dust are associated with concrete production. The measures that are necessary depend strongly on the location of the plant and the noise level generated by the equipment.

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Table 1.8 (Cont.) Comprehensive List of Green Concrete Technologies (fib, 2012). Key topics Green concrete technologies 4. Recycling of demolition The technologies for recycling construction waste in concrete producand demolition waste (C&DW) back into tion construction are already widely known and accepted. However, the major hurdle pertains to establishing economic incentives in order to make recycling an option. However, green procurement, especially by the authorities, will probably accelerate recycling in the future. The principal applications of recycled concrete rubble are as follows: - Down-cycling it for road sub-base and back-fill material in connection with construction work. As the quality and homogeneity of recycled concrete material varies significantly, it is mainly suitable for low-tech applications where performance is not a top priority. - Recycling it into concrete as a substitute for natural aggregates. This application is possible, and the performance of the recycled aggregate concrete can be satisfactory when compared with conventional concrete. 5. Construction phases One green measure during the construction phase is the use of self-desiccating concrete, which can minimize the energy needed to dry out the concrete in order to obtain the required moisture content. The following recommendations can be given: - Provide appropriate drying times for concrete before applying surface materials. - Be careful in regard to detailing to avoid flanking the transmission of noise in buildings.

24 Table 1.8 (Cont.) Comprehensive List of Green Concrete Technologies (fib, 2012). Key topics Green concrete technologies 6. Use of concrete For buildings, the appropriate use of exposed concrete on the inner walls can reduce the energy used for heating and cooling by approximately 5–15%. The exact savings depend on the climate, the orientation of the structure, how much of the concrete surface is exposed, and the ventilation system, etc. The following recommendations can be given: - Clarify and utilize the thermal mass effect in regard to energy use and thermal comfort. - Maximize the use of solar and other free energy gains by thermal storage. - Clarify and use the thermal mass effect in regard to the top effect requirement for heating and cooling systems. - Use energy calculation programs that take thermal storage into account. - Use low-energy sources by design for a low top effect. - Expose concrete surfaces for access to thermal storage.

Therefore, it is necessary to advance the industry’s understanding of concrete properties when using green raw materials, reduce the cost of recycling and reuse processes, improve industry standards, and educate the industry about new technologies.

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1.4 Green cement production Cement production has undergone tremendous development from its beginnings some 2,000 years ago. The use of cement in concrete has a very long history, with the industrial production of this material dating back to the middle of the 19th century, first with shaft kilns, which were later replaced by rotary kilns as the standard equipment worldwide. In contemporary times, annual global cement production has increased every year, and is expected to continue to increase by some 4 billion tons per year (Schneider et al., 2011). In 2014, annual global cement production reached 4.18 billion tons. Furthermore, major growth is foreseen in countries such as China and India, as shown in Table 1.9 (USGS, 2015). In regard to environmental implications, it is of critical importance to control excessive cement demand. In particular, it is important to consider the production of concrete in China, where is the potential for extremely large amounts of cement to be produced. Elimination of this excessive production could result in substantial reductions of CO2 emissions and local pollutants such as mercury and particulate matter without damaging economic development. Overall, it is critical that demand management and technological transfer are addressed effectively in approaching challenging global and local resource and environmental issues (Uwasu et al., 2014). Table 1.9 World Production of Cement (in Million Metric Tons). Country 2010 2011 2012 2013 China 1,880 2,100 2,210 2,420 India 210 240 270 280 United States 67.2 68.6 74.9 77.4 Iran 50 61 70 72 Turkey 61.7 63.4 63.9 71.3 Brazil 59.1 64.1 68.8 70 Russia 50.4 55.6 61.5 66.4 Saudi Arabia 41.3 48.4 50 57 Thailand 36.5 36.7 37 42 Other countries 851.8 861.2 893.9 923.9 World total 3,310 3,600 3,800 4,080 Increase (%) 8.76 5.55 7.36

2014 2,500 280 83.3 75 75 72 69 63 42 920.7 4,180 1.45

26 Cement will remain the key material for satisfying global housing and modern infrastructure needs. As a consequence, the cement industry worldwide is facing growing challenges in regard to conserving material and energy resources, as well as reducing its CO2 emissions (Schneider et al., 2011). Given that approximately 4.18 billion tons of cement are produced globally every year, the world carbon intensity of carbon emissions in cement production becomes a matter of some importance: the average world carbon intensity average is 0.81 kg of carbon dioxide per 1 kg of cement produced (Hendriks et al., 2004), which equates to 3.39 billion tons of CO2 per year. These figures do not include CO2 and other greenhouse gasses emitted during the quarrying and transport of raw materials or the loading, unloading, and transportation of the cement produced. The main sources of emissions in the OPC manufacturing process arise from two processes: (i) from the calcination process as described earlier, and (ii) from the combustion fuel used to heat the raw materials to sintering temperatures (1400–1600˚C). The amount of CO2 emitted depends on the type of fuel and the specific processing method used. Kilns are fired using coal, fuel oil, natural gas, petroleum coke, biomass, waste-derived alternative fuels, or mixtures of these fuels (Imbabi et al., 2012).The production process is shown in Fig. 1.3.

Fig 1.3 Share of total CO2 emissions across the Portland cement production process (Imbabi et al., 2012).

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The cement industry faces a number of challenges, which include the depleting fossil fuel reserves, the scarcity of raw materials, the perpetually increasing demand for cement and concrete, the growing environmental concerns linked to climate change, and an ailing world economy. On average, every ton of Ordinary Portland Cement (OPC) produced releases a similar amount of CO2 into the atmosphere, or put another way at current production levels OPC accounts for roughly 6% of all man-made carbon emissions. Improved production methods and formulations that reduce or eliminate CO2 emissions from the cement manufacturing process are, therefore, high on the agenda. Emission reduction is also needed to counter the impact on product cost of new regulations, green taxes, and escalating fuel prices (Imbabi et al., 2012). There are two major sources of CO2 emissions in the cement production process: the use of fossil fuel as an input and the chemical reactions that occur during production. The global average energy consumption per ton of cement produced is estimated at 5390 MJ. It is, therefore, of critical importance to install the best available technologies for cement production, as there is significant potential for reducing energy consumption in that area (Uwasu et al., 2014). Direct CO 2 emissions in the cement manufacturing process originate from two sources: Decarbonization of limestone during clinker formation, a necessary process in cement manufacture, and burning fuel to heat the materials in the clinker kiln to temperatures as high as 1450ºC. Moreover, indirect emissions from electric power consumption contribute another 10% to overall CO2 emissions (CSI, 2009a). The impact of the four key reduction levers available to the cement industry to reduce carbon emissions are (i) thermal and electric efficiency, (ii) alternative fuels, (iii) clinker substitution, (iv) carbon capture and storage (CCS) and limits to implementation, as shown in Table 1.10. It is often the case that each individual lever has an influence on the potential of another lever to reduce emissions. For example, the use of alternative fuels generally increases specific heat consumption (e.g., because of higher moisture levels). Therefore, simply adding up the reduction potential of each technology in order to calculate the total potential would not be accurate. The emission reduction potential is based on net emissions. (CSI, 2009b).

28 Table 1.10 Four Key Reduction Levers Reduce CO2 Emissions and Limit Implementation. Key reduction levers Limits to implementation Thermal and electric efficiency Deploy existing state-of-the-art • High investment costs and so retrotechnologies in new cement fits are limited. plants, and retrofit of energy• Strengthened environmental efficient equipment where requirements can increase power economically viable. consumption. • The demand for high-performance cement, which requires very fine grinding and uses more power. • It is generally accepted that CCS is key to reducing CO2 emissions, but it has been estimated to increase power consumption by 50–120% at the plant level. • Other reduction levers, for example clinker substitutes in the clinkerproduction process generally require more energy to grind cement finely. Alternative fuels Use less carbon-intensive • Pre-treatment, the physical and fossil fuels and more chemical properties of most alternative (fossil) fuels and alternative fuels differ significantly biomass fuels in the cement from those of conventional fuels, production process. Alternative often needed to ensure a more fuels include waste that may uniform composition and optimum otherwise be burnt in combustion. incinerators, deposited in land- • Waste management legislation fills, or improperly destroyed. significantly impacts availability: higher fuel substitution only takes place if local or regional waste legislation restricts land-filling or dedicated incineration.

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Table 1.10 (Cont.) Four Key Reduction Levers Reduce CO2 Emissions and Limit Implementation. Key reduction levers Limits to implementation • Local waste collection networks must be adequate. • Alternative fuel costs are likely to increase with high CO2 costs. It may then become increasingly difficult for the cement industry to source significant quantities of biomass at acceptable prices. The level of social acceptance such that people are often concerned about harmful emissions from co-processing. Clinker substitution Substitute carbon-intensive • Regional availability of clinkerclinker, an intermediate in substituting materials. cement manufacture, with • Increasing prices of substitution other, lower carbon, materials materials. with cementitious properties. • Properties of substitution materials and intended application of the cement. • National standards for Ordinary Portland Cement and composite cements. • Common practice and acceptance of the composite cements by construction contractors and customers. Carbon capture and storage (CCS) Capture CO2 before it is re• CCS could be applied in the cement leased into the atmosphere and industry only if the political framestore it securely so that it is not work effectively limits the risk of released in the future.

30 Table 1.10 (Cont.) Four Key Reduction Levers Reduce CO2 Emissions and Limit Implementation. Key reduction levers Limits to implementation carbon leakage (relocation of cement production into countries or regions with fewer constraints). Public support is critical and should be developed in a variety of ways: through political support, property owners’ cooperation, and local residents’ informed approval. It is important to educate and inform the public and key stakeholders about CCS.

Various levers can be used to reduce direct and indirect emissions, and individual performance indicators can show trends over time (CSI, 2009a), as shown in Table 1.11. Table 1.11 Levers and Performance Indicators for Cement Industry CO2 Emissions. Performance indicator Lever for CO₂ emissions management Thermal efficiency per ton of GJ per ton of clinker clinker Technology and plant/kiln Kiln type operations Fuel mix Fuel mix and thermal substitution of conventional fuels by alternative fuels and biomass Clinker substitutes Clinker to cement ratio Indirect emissions from electric Electric power per ton of cement power used Emissions performance Gross and net emissions per ton of cementitious products

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A number of low-carbon or carbon-negative cements are currently being developed by startup companies expecting to build pilot plants in 2010– 2011. These cements have not been proven to be economically viable, nor have they been tested at scale for long-term suitability. Further, the products have not been accepted in the construction industry where rigorous material and building standards exist. If and when the first production plants come on stream, initial applications are likely to be limited and apply to niche markets only, pending widespread availability and customer acceptance. It is, therefore, not known whether they will have an impact on the future cement industry. In the long term, they may offer opportunities to reduce the CO2 intensity of cement production such that their progress should be followed carefully and potentially supported by governments and industry as below:.  Novacem is based on magnesium silicates (MgO) rather than limestone (calcium carbonate), which is used in OPC. Global reserves of magnesium silicates are estimated to be large, but these are not uniformly distributed and processing would be required before use. The company’s technology converts magnesium silicates into magnesium oxide using a low-carbon, low-temperature process, and then incorporates mineral additives that accelerate strength development and CO2 absorption. This process offers the prospect of carbon-negative cement.  Calera is a mixture that combines calcium and magnesium carbonates with calcium and magnesium hydroxides. Its production process involves bringing sea water, brackish water, or brine into contact with the waste heat in power station flue gas, where CO 2 is absorbed, precipita ting the carbonate minerals (CSI, 2009b). Stanford Professor Brent Constantz presented this process for making green cement claiming that he has invented a green cement capable of eliminating the huge amounts of carbon dioxide spewed into the atmosphere by the manufacturers of the cement currently used in concrete for buildings, roadways, and bridges. Constantz claims that his approach not only generates zero CO2, but has the added benefit of reducing the amount of CO2 power plants emit by sequestering it inside the cement, as shown in Fig. 1.4. This is in contrast with the

32 manufacturing process of traditional cement, whereby limestone is heated to more than 1,000 degrees Celsius, which turns it into lime—the principal ingredient in Portland cement—and CO2, which is released into the air. At the pilot factory, Constantz outlines how his process works: two enormous smokestacks billow flue gases full of carbon dioxide next door at Dynegy, one of the West’s biggest and cleanest power plants. Constantz takes that exhaust gas and bubbles it through seawater pumped from across the highway. The chemical process creates the key ingredient for his green cement and allows him to sequester a half ton of carbon dioxide from the smokestacks in every ton of cement he makes. Constantz believes his cement could be used to tackle global warming on two fronts. It would eliminate the need to heat limestone, which releases CO1. And, harmful emissions can be siphoned away from power plants and locked into the cement (Sturrock, 2008).

Fig. 1.4 The making of green cement (Sturrock, 2008).

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 Calix’s cement is produced in a reactor by rapid calcination of dolomitic rock in superheated steam. The CO2 emissions can be captured using a separate CO2 scrubbing system.  Geopolymer cement utilizes waste materials from the power industry (fly ash, bottom ash), the steel industry (slag), and from concrete waste, to make alkali-activated cement. The performance of such a system is dependent on the chemical composition of the source materials, the concentration of sodium hydroxide (NaOH) and potassium hydroxide (KOH) chemical activators, and the concentration of soluble silicates. Geopolymer cements have been commercialized in small-scale facilities, but have not yet been used in large-scale applications where strength is critical. This process was developed in the 1950s. (CSI, 2009b) In recent years, the cement industry has made significant progress, specifically in regard to processes and energy savings. However, here, too, the last word has not been said in spite of the fact that, from a thermodynamic point of view, the CaO ± SiO2 ± Al2O3 ± Fe2O3 phase diagram still governs the manufacture of OPC. It is already possible to significantly decrease the temperature in cement kilns by more effectively controlling the use of what are referred to as mineralizers. Over time, the processes whereby OPC is produced have become more and more complex and more and more technical. These processes are not very robust, and require the use of powerful computing facilities to run expert systems that often require highly skilled personnel who may not be found in developing countries, to maintain them. Moreover, progress of a very interesting nature has been made in the field of sustainable development such that some cement plants are already safely eliminating numerous pollutants and/or industrial waste. Some cement plants are even producing cement at a negative cost because they are paid to eliminate these pollutants, which means that they start making money before selling even a single ton of cement (Aïtcin, P-C., 2000). To begin with, cement production focused only on OPC. However, eventually, cements with several main constituents were produced by replacing some of the clinker content with supplementary cementitious materials (SCM). As such, fly ash from coal power plants,

34 granulated slag from iron production as well as natural pozzolans are now used in increasing amounts. Also, limestone can be substituted for some of the clinker in cement. The substitution of clinker in cement is the most effective way to reduce the specific CO2 emissions per ton of cement, because only clinker is related to substantial fuel consumption and the calcination of limestone. In cement, the reduction of clinker remains a top priority, and, in fact, tremendous progress on this point has already been made. Nevertheless, appropriate materials are limited in terms of their regional availability. New materials could play a role as cement constituents in the future. The extent to which these are used to substitute for Portland cement clinker remains to be seen (Schneider et al., 2011). In this regard, locally available minerals, recycled materials and industry, agriculture, and domestic waste may be suitable for blending with OPC as substitute binders, or in some cases as replacement binders. Fly ash, blast furnace slag, and silica fume are three well-known examples of cement replacement materials that are in use today that, like OPC, have been documented and validated both in laboratory tests and in practice. The first is a by-product of coal combustion, the second of iron smelting, and the third of electric arc furnace production of elemental silicon or ferro silicon alloys (Imbabi et al., 2012). The cement industry has no choice: it must focus on this direction in determining its development and considering its constraints. The cement industry will, no doubt, succeed in making this change. The cement industry, or rather the hydraulic binders industry, which will eventually become how the cement industry is known, will be green in nature (Aïtcin, P-C., 2000). The most effective methods of producing green, environmentally and economically sustainable cements of the highest quality are (a) the use of alternative, low-carbon fuels and (b) the development of novel cement formulations and production methods (Imbabi et al., 2012). There is no choice in this. It is better, therefore, to face as soon as possible this new situation and transform the cement industry into in a green industry. There are numerous ways of becoming green, and it is important, too, that this commitment be made known to the public (Aïtcin, P-C., 2000).

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1.5 Concrete recycled materials The long-term approach to lowering the environmental impact of using any material is to reduce the rate at which it is consumed. For reasons that are discussed in the following sections, the rate of concrete consumption probably cannot be reduced for some 50 years. In the short-term, we must begin by practicing industrial ecology for sustainable industrial development. Simply stated, the practice of industrial ecology involves recycling the waste products of one industry by substituting them for the virgin raw materials of another industry, thereby reducing the environmental impact of both industries. Reportedly, over 1 billion tons (900 million tons) of construction and demolition waste are generated every year. Cost-effective technologies are available to recycle most of this waste as a partial replacement for the coarse aggregate used in fresh concrete mixtures. Similarly, industrial waste water and nonpotable water unless proven harmful by testing can be substituted for municipal water for mixing concrete. Blended Portland cements containing fly ash from coal-fired power plants and ground granulated slag from the blast-furnace iron industry provide excellent examples of industrial ecology because they offer a holistic way to reduce the environmental impact of several industries (Mehta, 2002). One of the ways in which the concrete industry can become more compliant with the demands of sustainable development is increased reliance on recycled materials. As aggregate constitutes the bulk of concrete, an effective recycling strategy will lessen the demand for virgin materials, and recycling of wash water is readily achieved in practice and already required by law in some countries (Meyer, 2005). The Cement Sustainability Initiative (CSI, 2009c) summarizes the myths and facts about concrete recycling, as shown in Table 1.11.

36 Table 1.12 Concrete Recycling: Some Myths and Facts. Myths Reality • Concrete cannot be recycled Although concrete is not broken down into its constituent parts, it can be recovered and crushed for reuse as aggregate (for use in ready-mix concrete or other applications) or it can be recycled through the cement manufacturing process in controlled amounts, either as an alternative raw material to produce clinker or as an additional component when grinding clinker, gypsum, and other materials used in cement. • Recycled concrete aggregate cannot be used for structural concrete

It is generally accepted that about 20% (or more) aggregate content can be replaced by recycled concrete for structural applications.

• Although some concrete can be recycled it is not possible to achieve high rates of recycling

Countries such as the Netherlands and Japan achieve near complete recovery of waste concrete.

• Concrete can be 100% made by recycling old concrete

Current technology means that recovered concrete can be used as aggregate in new concrete but that (1) new cement is always needed and (2) in most applications only a portion of recycled aggregate content can be used (regulations often limit this content as do physical properties, particularly for structural concrete).

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Table 1.12 (Cont.) Concrete Recycling: Some Myths and Facts. Myths Reality • Recycling concrete will Most greenhouse gas emissions from reduce greenhouse gases and concrete production occur during the the carbon footprint production of cement. Less-significant savings may be made if transportation needs for aggregates can be reduced by recycling. • Recycling concrete into lowgrade aggregate is downcycling and is not the best solution environmentally

A full lifecycle assessment should be undertaken. Sometimes low-grade use is the most sustainable solution, as it diverts other resources from the project and uses minimal energy in processing. That is not to say more refined uses might not also suit a situation.

• Recycled aggregate is more expensive than traditional aggregate

This depends on local conditions (including transportation costs).

• Demolition concrete is inert

Compared to other waste, concrete is relatively inert and does not usually require special treatment.

• Recycled concrete can be better than virgin aggregate for some applications

The physical properties of coarse aggregate made from crushed demolition concrete make it the preferred material for applications such as road base and sub-base. This is because recycled aggregate often has better compaction properties and requires less cement for sub-base uses. Furthermore, it is generally cheaper to obtain than virgin material is.

38 Table 1.12 (Cont.) Concrete Recycling: Some Myths and Facts. Facts Rationale • Using recycled aggregate By using recycled aggregate in place reduces the land-use impact of virgin materials (1) less landfill is generated and (2) fewer natural resources are extracted. • Recycling all construction and demolition waste (C&DW) will not meet market needs for aggregate

Even near complete recovery of concrete from C&DW will only supply about 20% of total aggregate needs in the developed world.

• Figures are not complete for recovery rates

Data are often not available. When data are available, different methods of counting make crosscountry comparisons difficult.

The concrete industry has become a victim of its own success and, therefore, is now faced with tremendous challenges. But the situation is not as bad as it appears, because concrete is inherently an environmentally friendly material. The challenges listed above are more a result of the fact that Portland cement is not particularly environmentally friendly. These challenges, therefore, can be reduced to the following simple formula: use as much concrete as necessary, but with as little Portland cement as possible. This means that as much Portland cement as possible should be replaced by supplementary cementitious materials (SCM), especially those that are by-products of industrial processes. It also means that recycled materials should be used in place of natural resources. Foremost is the increasing use of cementitious materials that can serve as partial substitutes for Portland cement, particularly materials that are by-products of industrial processes, such as fly ash and ground granulated blast furnace slag. But also the substitution of various recycled materials for aggregate has made significant

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progress worldwide, thereby reducing the need to quarry virgin aggregates. The most important among these are recycled concrete aggregate, postconsumer glass, scrap tires, plastics, and by-products of the paper industry and of other industries. The principles of sustainable development and green buildings have penetrated the construction industry at an accelerating rate in recent years. The potential tools and strategies to meet the environmental challenges can be summarized as follows (Meyer, 2009): 1) Replace as much Portland cement as possible with supplementary cementitious materials (SCM), especially those that are by-products of industrial processes, such as fly ash, ground granulated blast furnace slag, and silica fume. 2) Use recycled materials in place of natural resources. 3) Improve the durability and service life of structures, thereby reducing the amount of materials needed to replace them. 4) Improve concrete’s mechanical and other properties, which can also reduce the amount of materials needed. 5) Reuse wash water. What started as a demand by a few environmentalists has now been adopted by the public at large and by governments on local, state, and national levels. By the end of the 20th century, sustainable development and environmental protection became key goals of modern society. The important role in the sustainable development of the built environment, the reduction of pollution, the conservation of natural resources, and the realization of energy savings has certainly caught the attention of the entire civil engineering industry, but especially of the construction materials industry. In this context, the main problems that the industry faces (Radonjanin et al., 2013) are as follows:  Natural aggregate depletion  High consumption of Portland cement and associated high emission of carbon dioxide  Large amount of generated construction and demolition (C&D) waste and land fill space depletion

40 Jin and Chen (2013) presented survey results on the current status of green raw material usage in the U.S. concrete industry. Despite a large number of academic studies on various types of supplementary cementitious materials (SCM) and alternative aggregates (AA), companies differ considerably in recognizing and utilizing SCMs and AAs. Therefore, a green raw material already being used by some concrete companies might still be new to their peers. As shown in Table 1.13, the top three most frequently mentioned benefits and concerns related to the use of SCMs were the same: impact on concrete properties, costs, and local availability. Among these, the properties of concrete were the most important factor in considering whether to use an SCM. It should also be noted that an advantage of using an SCM for one concrete company could be a disadvantage for another. Additionally, in the survey, many suppliers/ manufacturers may not have been aware of the use of green materials in concrete production, as only 2% of them listed the reuse of waste materials as beneficial. Regarding the disadvantages associated with using SCMs, slowing/hindering production and the lack of specifications or restrictions from authorities were two frequently mentioned barriers. In regard to the use of AAs, this could be due to the limited knowledge and experience of concrete industry practitioners in regard to AAs. No specifications were mentioned in regard to the use of AAs, with the exception of lightweight aggregates. The top three benefits and barriers of using AAs are not consistent. The structural advantages and cost savings were widely recognized by the industry. Up to 19% of the survey participants knew that using AAs constitutes an approach to being green, which they understood could save natural resources and reuse waste streams. Evidently, there are numerous options for by-product recycling in the production of concrete Naik (2002). For example, foundry sand can be used to replace regular sand in Portland cement concrete, cast-concrete products, controlled low-strength materials (CLSM), and other cementbased materials. Cupola slag from steel and iron foundries can also be used successfully in making semi-lightweight structural concrete. Post-consumer glass can be used as a partial replacement for fine aggregate in regular and flowable concrete, as well as in CLSM, with Class F coal fly ash in the amounts needed to control ASR expansion. Structural-grade concrete and

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cast-concrete products have been manufactured using wood fly ash, which have significant pozzolanic properties and are typically more reactive than natural pozzolans, but less reactive than ASTM Class C coal fly ash. Concrete containing residual solids from pulp and paper mills and paperrecycling plants exhibit improved resistance to chloride-ion penetration and freezing and thawing of concrete without loss of strength. The addition of recycled materials can improve the quality of concrete while reducing the amount of waste deposited in landfills. Table 1.13 Benefits of and Barriers to the Use of SCMs and AAs. Benefits of using SCMs and Barriers to using SCMs and AAs AAs Supplementary cementitious material (SCM)  Improved concrete properties 41%  Cost savings 28%

 Lower quality 25%

 Local availability 17%

 Local availability 17%

 Aid to concrete production 7%  Other 7%

 Slowed/hindered production 15%

 Increased cost 25%

 Lack of specifications/restrictions from authorities 12%  Other 6%

Alternative aggregate (AA)  Cost savings 30%

 Increased cost 34%

 Structural advantage 30%

 Slowed/hindered production 13%

 Being green 19%

 Lower quality 4%

 Local availability 13%

 Local availability 23%

 Improved concrete properties 5%

 Technical barriers related to aggregate 17%

 Usability 3%

 Other 9%

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1.5.1 Recycled materials used to replace natural aggregate Reduce, reuse, and recycle in order to respect the environment and foster its recovery from overexploitation are the key principles of a sustainable construction material. Considerable research has been conducted regarding the use of recycled concrete aggregate (RCA) in concrete mixes recycled from parent concrete of natural source aggregate, referred to here as first generation. Recycling the RCA thereby forming a second loop of recycling concrete is referred to here as second-generation RCA. As aggregates generally account for 70–80% of concrete volume, they should be selected carefully in order to control the quality of the concrete. The demolition phase of the lifecycle of concrete plays a significant role in the recycling process and should be handled on the basis of extensive precautions and testing. The end of the life-recycling process is a method used to minimize the environmental impact of products by employing sustainable production, operation, and disposal practices with the aim of developing products in accord with a sense of social responsibility. Fig. 1.5 represents a closedloop lifecycle of concrete material.

Fig. 1.5 Lifecycle of concrete material for first- and second-generation concrete (Marie and Quiasrawi, 2012).

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Marie and Quiasrawi (2012) studied the properties of second-generation concrete. The concrete mixes considered in this study are conventional mixes made of 100% natural aggregate (NA) and up to 20% replacement of NA with RCA. In this way, first-generation concrete and mixes containing up to 20% replacement of NA with aggregate were obtained by recycling first-generation concrete (R-RCA). The results show that the use of RCA and R-RCA has an adverse effect on the properties of concrete. However, using RCA or R-RCA to replace up to 20% of NA by RCA produces concrete of acceptable quality. The second-generation RCA performed better than the first-generation RCA did. The researchers also showed that closed-loop recycling is possible and noted the advantages of fostering the sustainability of natural resources and the environment. Nevertheless, some key factors that could affect the properties of recycled aggregate concrete have not been thoroughly investigated, such as the proportion of recycled aggregates, the moisture state of recycled aggregates, and the design compressive strength of concrete. In particular, little research has been conducted on the combined effects of recycled aggregates and fly ash, popularly used as a partial substitute for cement. Given the concerns, Kim et al. (2013) investigated the effects of such factors on the mechanical and durability properties of recycled aggregate concrete. In general, the higher ratio of recycled aggregates resulted in concrete with better flowability. Also, the use of fly ash improved the flowability of recycled aggregate concrete. The strength test results showed that the higher ratio of recycled aggregates generally resulted in concrete with lower compressive and tensile strengths than that of conventional concrete. However, the cases with 30% recycled aggregates showed only slight compressive strength reductions. Similarly, the use of fly ash caused only small reductions in the compressive strength of recycled aggregate concrete. In contrast, the negative effects of recycled aggregates and fly ash were greater on the tensile strength of concrete than on its compressive strength. Lastly, the cases containing fly ash exhibited much higher resistance to chloride penetration, even in the cases with recycled aggregate. The correlation between the time evolution of the degree of hydration and the compressive strength of Recycled Aggregate Concrete (RAC) for the different water to cement ratios and initial moisture conditions of the

44 RCAs is addressed by Koenders et al. (2014). In particular, the researchers investigated the influence of the moisture conditions by monitoring the hydration process and determining the compressive strength development of fully dry or fully saturated recycled aggregates in four RAC mixtures. The hydration processes were monitored via temperature measurements in hardening concrete samples, and the time evolution of the degree of hydration was determined through a 1-day hydration and heat flow model. In fact, a novel conceptual method is proposed to predict the compressive strength of RAC-systems from the initial mixture parameters and the hardening conditions. Given increasing concern over the excessive exploitation of natural aggregates, synthetic lightweight aggregate produced from environmental waste is a viable new source of structural aggregate material. The use of structural grade lightweight concrete considerably reduces the self-load of a structure and permits larger precast units to be handled. Lo and Cui (2004) investigated the mechanical properties of a structural-grade lightweight aggregate made with fly ash and clay. Their findings indicate that water absorption of the green aggregate is large but that the crushing strength of the resulting concrete can be high. The 28-day cube compressive strength of the resulting lightweight aggregate concrete with a density of 1590 kg/m3 was 34 MPa. Hameed and Sekar (2009) studied the properties of green concrete containing quarry rock dust and marble sludge powder as fine aggregate and the feasibility of the usage of quarry rock dust and marble sludge powder as 100% substitutes for natural sand in concrete. Marble sludge powder can be used as filler and helps to reduce the total void content in concrete. Natural sand in many parts of the country is not graded properly and has excessive silt. On other hand, quarry rock dust does not contain silt or organic impurities and can be produced to meet specific gradation and fineness requirements. Consequently, this plays a role in improving the strength of the concrete. Through a reaction with the concrete admixture, marble sludge powder and quarry rock dust improved the pozzolanic reaction, micro-aggregate filling, and concrete durability. An attempt has been made to perform a study on green concrete in order to compare its performance with that of natural sand concrete. It was found that the

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compressive, split tensile strength and durability of concrete made of quarry rock dust are nearly 14% higher than those of conventional concrete. The concrete’s resistance to sulphate attack was also enhanced greatly. Application of green concrete is an effective way to reduce environment pollution and improve durability of concrete under severe conditions. Bhimani et al. (2013) presented results from their study on concrete with a mix proportion of 1:1.48:3.21 in which cement was partly replaced by Pozzocrete P60 at 30% by weight of cement and in which fine aggregate was partly replaced by used foundry sand obtained from ferrous and non-ferrous metal casting industries at 10%, 30%, and 50% by weight of fine aggregate. This research was performed with the purpose of modelling the potential technical, ecological, and economic benefits of using large amounts of used foundry sand and Pozzocrete, both of which are produced every year, in India and elsewhere. Sheen et al. (2014) investigated the engineering properties of green concrete containing stainless steel oxidizing slag (SSOS) to determine the best substitution proportion of SSOS for fine and coarse aggregates. Their results show that when SSOS is used to replace 100% of natural fine aggregate the mortar produced has better compressive strength than when natural fine aggregate is used. A 100% SSOS substitution also produces better hardened concrete properties, such as compressive strength, surface resistance, and ultrasonic pulse velocity (UPV), than natural coarse aggregate does. Furthermore, X-ray diffractometer (XRD) and energy dispersive spectrometer (EDS) microstructure analyses show that the calcium hydroxide (CH) content tends to decrease with increasing SSOS aggregate substitution and further that the alkaline elements sodium (Na) and potassium (K) dissolve into the mortar and coarse aggregate interfaces. These alkaline-reducing agents help make the concrete more durable. Additionally, heavy metals do not leach from SSOS concrete. Therefore, SSOS can be considered a green concrete material, as it is made from a recycled resource. Sheen et al. (2014) showed that the optimal aggregate replacement ratio for SSOS is 100%. Therefore, stainless steel oxidizing slag may qualify as an aggregate for green concrete materials. This practice would reduce stainless steel slag waste, thereby contributing to recycling and environmental protection.

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1.5.2 Recycled materials as a replacement for aggregate in concrete The engineering and transport properties of high-strength green concrete (HSGC) containing up to 60% of ultrafine palm oil fuel ash (POFA) have been studied by Megat Johari et al. 2012). POFA obtained from the palm-oil industry was subjected to heat treatment to remove excess carbon and ground to a median particle size of about 2 m. The ultrafine POFA obtained was then utilized in the production of HSGCs with POFA replacement levels of 0%, 20%, 40%, and 60% by mass of ordinary Portland cement. The results show that the treatment processes undertaken result in a highly efficient pozzolan. For fresh concrete, the inclusion of ultrafine POFA tends to increase the workability of the HSGCs and retards the setting time in particular at higher POFA content. In terms of compressive strength, the inclusion of ultrafine POFA reduces the early-age strength of the HSGCs at 1, 3, and 7 days, but enhances strength at 28 days for all HSGCs containing POFA. In fact, at 28 days, strength exceeding 95 MPa was achieved for all the POFA–HSGCs. The transport properties as assessed in reference to porosity, initial surface absorption, rapid chloride permeability, gas permeability, and water permeability tests significantly improved with the inclusion of ultrafine POFA, with the HSGC containing 60%. However, POFA showed the greatest improvement at 28 days. Thus, the overall results show that ultrafine POFA has significant potential as an efficient pozzolanic mineral admixture for the production of HSGC with engineering and transport properties. In addition, Aldahdooh et al. (2013) presented an ideal experimental design based on the response surface method (RSM) in order to develop a new class of Green Ultra-High Performance Fiber Reinforced Cementitious Composites (GUHPFRCCs), in which 50% of the volume consists of ultrafine palm oil fuel ash (UPOFA). This green concrete, currently under development at the Universiti Sains Malaysia (GUSMRC), could lead to greater use of POFA in concrete. Eventually, such greater use could be useful in efforts to protect the environment by minimizing the volume of waste disposed of in wasteland and minimizing the emission of greenhouse

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gases released during cement production, in addition to contributing to cost savings and to the sustainability of the concrete industry. The results show that at 90 days the optimum mix achieved was 158.28 MPa, 46.69 MPa, and 13.78 MPa of compressive strength, bending tensile strength, and direct tensile strength, respectively, with UPOFA replacing 50% of the total standard binder content. This indicates the potential of UPOFA as an efficient pozzolanic mineral admixture in the production of GUSMRC with the promise of superior engineering properties. Moreover, zeolite, a type of natural pozzolanic material, has been used as an alternative to improve the durability of concrete. The environmental impact of concrete containing zeolite and conventional cement materials on global-warming potential are assessed by applying the lifecycle assessment method. The calculations indicate that replacing 10%, 20%, and 30% of cement with zeolite amounted to a 60.3%, 69.7%, and 64.3% reduction in global-warming potential, respectively, which proves the effectiveness of zeolite in making concrete that is very environmentally friendly (Valipour et al., 2014).

1.5.3 Recycled materials with no cement The potential of inorganic polymers (geopolymers) as an element in the creation of a sustainable concrete industry is discussed by Duxson et al. (2007). Geopolymers are alkali-activated aluminosilicates, with a much smaller CO2 footprint than that of traditional Portland cements. Further, the geopolymers have very good strength and chemical-resistance properties as well as a variety of other potentially valuable characteristics. It is well known that the widespread uptake of geopolymer technology is hindered by a number of factors, in particular issues to do with a lack of long-term (20+ years) durability data in this relatively young research field. There are also difficulties in terms of this technology’s compliance with some of the regulatory standards in Europe and North America, specifically those defining minimum clinker content level and the chemical composition of cement. Work on resolving these issues is ongoing, with accelerated durability testing showing very promising results in regard to salt scaling and freeze–thaw cycling. Geopolymer concrete compliance with performance-based standards

48 is comparable to that of most other high-strength concretes. Issues relating to the distinction between geopolymers synthesized for cement replacement applications and those tailored for niche ceramic applications are also discussed. Particular attention is paid to the role of free alkali and silicate in poorly formulated systems and the deleterious effects of each of these on concrete performance. Given this context, it is necessary to achieve a more complete understanding of the chemistry of geopolymerisation for the technology to be successfully applied. The relationship between the CO2 footprint and composition in comparison with Portland-based cements is quantified. Moreover, the disposal and treatment of hazardous industrial waste is very costly for the industry, such that this it has been a dormant issue. The recycling of waste and byproducts is attracting increasing interest worldwide due to the high environmental impact of the cement and concrete industries. Normal concrete is manufactured using sand and stones, but lightweight concrete can be made by using industrial by-products and hazardous solid waste such as expanded fly ash, slag, sludge, etc. The Best Demonstrated Available Technology (BDAT) stabilization/solidification (S/S) can be used to treat concrete contaminated with solid hazardous waste and by-products. Cement is replaced by the 15–35% fly ash in the concrete mix. Fly ash increases the strength of the concrete, improves its sulfate resistance, decreases its permeability, reduces the water ratio required, and improves its workability. Partial substitution of solid hazardous waste for cement does not have a significant effect on the strength of concrete or on any of its other properties. This mixed lightweight concrete is safe enough to use in sustainable environmental applications, such as roadbeds and for filling materials (Badur and Chaudhary, 2008). Recently, Long et al. (2015) presented an account of the relationship between the mixing proportion parameters of self-compacting concrete (SCC) and its environmental impact and of how to develop greener SCC. The researchers propose three simple indices combining the embodied environmental impact with the engineering properties of SCC. Their results indicate that the ecological impact index of SCC depends to a great extent on the mixing proportions. The addition of a high volume of mineral admixtures (such as 50%) can both effectively reduce the e-CO2 and e-resource indices and decrease the e-energy index.

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Selecting a reasonable aggregate volume can help decrease the environmental impact of SCC. Regardless of the mixing proportion parameters, the e-CO2, e-energy, and e-resource index of SCC both decrease with the increasing compressive strength of SCCs in the range of 30 to 60 MPa. Professionals involved in the cement and concrete industries have a responsibility to generate lasting innovations to protect the industries’ future viability and the health of our environment. Large volumes of by-product materials are generally disposed of in landfills. Because of stricter environmental regulations, the disposal costs for by-products are escalating rapidly. Recycling and creating sustainable construction designs not only contribute to reducing disposal costs but also aid in conserving natural resources. This conservation provides technical and economic benefits. It is necessary for those involved in the cement and concrete industries to eliminate waste and take responsibility for the lifecycle of their creations. To be responsible, it is necessary for engineers to think about the ecology, equity, and economy of their designs (Naik, 2008). However, the technical barriers to using alternative aggregate have been identified as a major disadvantage. These include the difficulty of controlling the alternative aggregate gradation and the complexity of the mix design. In addition, the lack of data on how alternative aggregate affects the long-term properties of concrete is also considered to be a significant disadvantage. Current barriers and benefits relating to the greater use of recycled concrete are detailed in Table 1.14. The Cement Sustainability Initiative (CSI, 2009d) has been looking at the recycling of concrete as a component of better business practices for sustainable development. Concrete has distinctive properties, and its recovery often falls between standard definitions of reuse and recycling. Concrete is broken down into aggregate for use in a new life. This new life is usually as aggregate for road works, but in some areas it is also used as aggregate in new concrete. Some countries have achieved near full recovery of concrete. However, in many parts of the world, the potential to recover concrete is overlooked, and it unnecessarily ends up as waste in a landfill. Furthermore, concrete waste statistics are generally difficult to secure. This is partially explained by the relatively low hazard that the waste poses compared with that of some other materials, resulting in low public concern.

50 Table 1.14 Some Key Barriers and Benefits cled Concrete (CSI, 2009c). Issue Barriers Material cost Low economic cost of vis-à-vis virgin aggregate in some natural aggre- countries. gate

Availability of material

Non-regular supply of C&DW. C&DW on-site waste management plans are needed.

Processing infrastructure

C&DW may need to be sorted. High-value recovered concrete requires costly processing. Misconception that recovered concrete is of lower quality than standard concrete. New materials are perceived as being of better quality. Classification of recovered concrete as waste can increase reporting and permit requirements. Extra limitations can be placed on use.

Public attitude

Laws, regulations, and industry standards

Related to the Use of RecyBenefits Aggregate levies and transportation costs for natural aggregate can be higher. Overall project costs can be reduced, as less landfill taxes/fees are paid on C& DW given that the material is recovered instead of going to a landfill. C&DW is usually found in urban areas near construction and development projects. Virgin materials must often be transported over greater distances. Once infrastructure is established, mobile sorting units and dedicated facilities can provide good returns. Increasing environmental concerns leading to increased demand for ecofriendly products and reuse of materials. Positive recycling laws, landfill taxes, and green procurement policies by large users can all promote recycled concrete use.

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Table 1.14 (Cont.) Some Key Barriers and Benefits Related to the Use of Recycled Concrete (CSI, 2009c). Issue Barriers Benefits Environmental Processing technology for Within a lifecycle analysis, impact the recovery of concrete the use of recovered should consider possible concrete can lower overall air and noise pollution environmental impact. impact as well as energy • Failing to use recovered consumption, although materials increases there is little difference landfill and associated between this processing environmental and health and the processing of natcosts. ural aggregates on these • Failing to use recovered points. materials means virgin materials are used instead. • Recovered concrete is generally inert. • In some cases, transportation needs for recycled concrete can be lower than for virgin materials (often not located in urban development areas) and as such fuel consumption, CO2 emissions, and road and vehicle use can be reduced. Physical properties

For specialized applications (e.g., highperformance concrete), there are some limitations on fitness for use. Technology can also limit recycling options.

For most uses, recycled concrete performs well.

52 Recovering concrete has two main advantages: (i) it reduces the use of virgin aggregate and its associated environmental costs pertaining to exploitation and transportation, and (ii) it reduces unnecessary landfill of valuable materials that can be recovered and redeployed. Recovering concrete, however, has no appreciable impact in terms of reducing greenhouse gas emissions. In the product lifecycle of concrete, the main source of carbon emissions is the cement production process (cement is added to aggregate to make concrete). The cement content in concrete cannot be viably separated and reused or recycled to make new cement, and thus carbon reductions cannot be achieved by recycling concrete. Finally, the economic feasibility of recycling depends largely on the application. In general, virgin materials have a quality control advantage over recycled materials. But the economic feasibility of recycling will improve in time, as virgin materials become increasingly scarce and the disposal costs of construction debris and other waste materials continue to increase. More importantly, we will see a proliferation of green building and sustainability development principles, which will modify the economic picture in favor of the environment. We all agree that we cannot keep wasting our natural resources. It is ultimately up to governmental authorities to level the playing field by holding producers responsible for the costs associated with the disposal of their products, whether these are associated with reuse, recycling, or landfilling. In many European countries, this is already the law and forces manufacturers to design their products with those disposal costs in mind. In other words: let him who pollutes pay for the cleanup (Meyer, 2005).

1.6 Green cement and concrete composites Concrete is a composite construction material made by mixing cement, aggregate (generally coarse aggregate made of gravel or crushed rocks, such as limestone or granite, plus a fine aggregate such as sand), water, and admixtures (if required). The proportionate quantity of each material affects the properties of hardened concrete. Due to various environmental concerns and the need for energy conservation, various research studies have focused on the use of various waste materials in the production of

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concrete (Bhimani, 2013). Cement is still an essential material in making concrete. However, in some modern concretes cement is no longer the most important material because these concretes are composite. In a composite material, it is impossible to decide which is the most important material because, by its nature, a composite material has properties that cannot be determined by simply adding together the individual properties of each component (Aïtcin, 2000). In reference to green cement and concrete composites that means substituting mineral admixtures and recycled aggregate for cement to some extent is an essential aspect in the development of green concrete. Radonjanin et al. (2013) presented the results of an experimental investigation of concrete made with recycled concrete aggregate, low cement content, and a high content of different mineral supplements. As they have less impact on the environment, help in solving the problem of construction and industrial waste disposal, and contribute to the conservation of natural resources, such concretes belong to the ranks of green or eco concretes. For green recycled aggregate concrete (GRAC), fine river aggregate and coarse recycled aggregate were used and 50% of cement by weight was replaced by a variety of inert, pozzolanic, and highly reactive mineral admixtures: milled limestone, fly ash, silica fume, and metakaolin. Test results showed that the optimal combination of different mineral admixtures can reduce the basic disadvantage of concrete with a high mineral supplement content: i.e., the relatively low strength of this kind of concrete in the period up to 28-day age, which allows certain structural applications of this type of green concrete. Huang et al. (2013) reported on the development of Green Lightweight Engineered Cementitious Composites (GLECC) with a high volume of industrial waste. Three types of industrial waste, i.e., iron ore tailings, fly ash, and fly ash cenosphere, were used as aggregate, mineral admixture, and lightweight filler, respectively, in the production of GLECC. Fly ash cenosphere was most advantageous in reducing density and thermal conductivity, while improving the tensile ductility of GLECC with only a slight reduction in compressive strength. The GLECC mixtures developed in this study utilized industrial waste at up to about 89% by volume of total solid matrix materials and weighed under 1850 kg/m3. Yet, the mechanical

54 properties of these mixtures are similar to that of ultra-ductile ECC with the added advantage of lower thermal conductivity for energy conservation when used as a building material. The cement and aggregate used in lightweight aggregate concrete were replaced with recycled green building materials as a fine aggregate (waste LCD glass sand was mixed with waste tire rubber particles). The findings showed that with the addition of recycled green building materials, the concrete maintained good workability even as the amount used to replace cement and standard aggregate increased. The unit weight decreased by approximately 1.4 times (600 kg/m3); the setting time and bleeding rate increased by 1.5 times (73 min and 190 min) and 1.4 times (8%), respectively. The compressive strength, ultrasonic pulse velocity (UPV), and length change decreased by 9.8 times (37.18 MPa), 1.4 times (1131 m/s), and 3.7 times (-0.115%), respectively. And, resistance increased by 1.8 times (27.8 k cm). A database will be constructed in the future for related studies to facilitate an increase in waste recycling value and to maximize the environmental protection benefits (Chen et al., 2013). Moreover, Xue and Shinozuka (2013) studied rubberized concrete composite as a new structural material with the purpose of improving the energy-dissipation ability and, therefore, the seismic performance of concrete by including recycled rubber crumb in the mix. It was observed that the damping coefficient of the rubberized concrete increased by 62% compared with normal concrete and, as a result, the seismic response acceleration of the structure decreased by 27%. However, the concrete suffered from a reduction in compressive strength as the rubber crumb was added. It was found that adding silica fume to rubberized concrete improved the bonding between the rubber and cement and, thus, the concrete strength. Overall, this study demonstrated the potential of using environmentally friendly rubberized concrete as structural material to improve the dynamic performance and reduce the seismic response of concrete structures. Agro-concrete or green concrete is composed of A mix between granulates from lignocellular plant (directly or indirectly from agriculture or forestry origin), which form the bulk of the volume, and a mineral binder. This definition does not cover mixtures that include a low proportion of lignocellular granulates and lignocellular plant fibers to reinforce conven-

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tional concrete. Indeed, many projects aim to create construction materials using one or more types of lignocellular material to reinforce a structure rather than as lightweight fibers for the purpose of insulation. When added to concrete, fibers improve the tensile strength, ductility, and post-fracture behavior of composite concretes. Sellami et al. (2013) improved the mechanical properties of green concrete by subjecting Diss-based vegetal fibers to one of two types of treatments in order to assess the efficiency of each. Diss is a wild vegetal species that is plentiful on the shores of the Mediterranean Sea. Similar to classical steel or polypropylene-reinforced concrete, this fibrous plant can be used to reinforce concrete. However, good adhesion between the fibers and cement is required for the fibrous strengthening to take effect. The use of particles from agricultural lignocellulosic resources in concrete gives it desirable environmental and multiphy sics qualities. Nozahic et al. (2012) studied the parallels drawn between particles derived from hemp and sunflower stems in terms of their morphological and physical properties as plant aggregate characterization. A pumice–lime binder is proposed as an alternative to the traditional cement- or lime-based solutions for both environmentally friendly and mechanical qualities. Compaction is applied during casting, and its effects on the mechanical properties of concrete are analyzed. A principal finding of this study is that the hemp and sunflower materials show strong similarities in terms of the morphology and mechanical performance of the resulting concrete. The pumice–lime binder provides desirable properties even with raw pumice sand, which represents 90% of the binder mass proportion. The compaction level during casting induces an orthotropy, even with low plant content, and increases the compressive strength. A simple analytical model using the Powers’ equation is proposed to predict the compressive strength of concrete in which low quantities of plant are used.

1.7 Green ready-mixed concrete The use of ready-mixed concrete has been a subject of debate as far back as the 1870s. A well-known British civil engineer, George Deacon, commented

56 in 1872 that If concrete were supplied to the site as a ready usable product this would without doubt, provide considerable advantages. Toward the end of the nineteenth century, some contractors were mixing their own supplies and hauling them for use on site but the concept was never adopted widely. The breakthrough came in the USA where the scale of construction created a demand for building materials in large volumes. The first recorded delivery of sold ready-mixed concrete was made in Baltimore in 1913. The next step in the development of ready-mixed concrete came in 1916 when Stephen Stepanian applied for a truck mixer patent but was unsuccessful. It was not until much later, in 1926, that the transit-mixer was born and the first concrete delivered in a truck mixer. Rapid development in the USA led to some 52% of cement produced being used by the ready-mixed industry in 1959 (Crompton, 2003). The acceptance and growth of the ready-mixed concrete industry between 1954 and 1974 was quite remarkable, with 31 million cubic meters per year being produced at the peak. The downturn in the construction industry was naturally reflected in the concrete production with the period of rationalization and consolidation that followed. The short history of the ready-mixed industry has been dominated by the need to produce and deliver a high-quality product at a reasonable cost (Dewar and Anderson, 1992). However, it should be noted that concrete is produced as ready-mixed concrete, site-mixed concrete and precast concrete products. Fig. 1.6 shows the production types of concrete in Europe and the United States. It reveals that Europe has a lower production percentage in ready-mixed concrete and higher on site-mixed and precast concrete compared with the United States (Sakai and Noguchi, 2012). The fact that most in-situ concrete is now supplied ready-mixed is a measure of how successful the industry has become, in terms of quality, service, and price to the customer (Dewar and Anderson, 1992). Ready-mixed concrete, in its basic form, is composed of cement, water, and aggregates. Water, sand, stone, or gravel, and other ingredients make up about 90% of the volume of concrete mixtures, as shown in Fig. 1.7.

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Fig 1.6 Comparison of types of concrete produced in Europe and the United States.

Fig 1.7 Typical composition of concrete by volume.

58 The process of mining sand and gravel, crushing stone, combining the materials at a concrete plant, and transporting concrete to the construction site requires comparatively little energy and, therefore, emits a relatively small amount of CO2 into the atmosphere. The amounts of CO2 embodied in concrete are primarily a function of the cement content in concrete mixtures. Concrete uses between about 7 and 15% cement by mass depending on the performance requirements. The average quantity of Portland cement is around 250 kg/m3, although the average has consistently decreased with better optimization of concrete mixtures and increased use of supplementary cementitious materials (SCMs), which can improve the strength and durability characteristics of concrete. As a result, approximately 100 to 300 kg of CO2 is embodied in every cubic meter of concrete produced or approximately 5 to 13% of the weight of concrete produced, depending on the mixture proportions. It is also documented that a significant portion of the CO2 produced during cement manufacturing is reabsorbed into concrete during the product’s lifecycle through a natural process called carbonation (Lemay and Lobo, 2010). In general, concrete is produced at a concrete plant where the ingredients are precisely measured and loaded into a plant mixer or directly into the drum of a concrete mixer truck using automated batching equipment. The mixing unit turns at a fast speed to thoroughly mix the ingredients in order to ensure the consistency needed. The majority of concrete is delivered to the construction site in concrete mixer trucks. Once at the site, the concrete is discharged from the mixer into forms that mold the concrete into its final shape. Construction crews often use special pumps and conveyors to move concrete to its final location (NRMCA, 2009a). The European Ready Mixed Concrete Organization (ERMCO) reported the ready-mixed concrete industry statistics in the several years with ERMCO members are the National Associations of ready mixed concrete producers. Data are presented separately for ERMCO members belonging to EU Countries, for all full ERMCO members, for corresponding member Russia and associated members USA and Japan, as shown in Table 1.15.

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Table 1.15 Ready-Mixed Concrete Production with ERMCO Members (ERMCO, 2014). Total production Production per capi3 Country (millions of m ) ta (m3/capita) 2011 2012 2013 2011 2012 2013 Austria 10.5 10.6 10.5 1.3 1.3 1.2 Belgium 11.6 11.5 11.5 1.1 1.1 1.1 Czech Republic 7.5 6.9 6.5 0.7 0.7 0.6 Denmark 1.1 1.0 1.3 0.4 0.4 0.4 Finland 3.0 1.7 1.7 0.6 0.5 0.5 France 41.3 38.9 38.6 0.6 0.6 0.6 Germany 48.0 46.0 45.6 0.6 0.6 0.6 Ireland 1.4 1.4 1.4 0.5 0.5 0.5 Italy 51.6 39.9 31.7 0.9 0.7 0.5 Netherlands 8.8 7.3 6.6 0.5 0.4 0.4 Poland 23.7 19.5 18.0 0.6 0.5 0.5 Portugal 6.1 3.7 1.7 0.6 0.3 0.3 Slovakia 1.3 1.9 1.7 0.4 0.3 0.3 Spain 30.8 21.6 16.3 0.7 0.5 0.3 Sweden 3.3 3.3 0.4 0.3 United Kingdom 19.2 17.6 19.6 0.3 0.3 0.3 Average EU 273.2 236.8 217.7 0.6 0.5 0.5 Israel 11.0 13.0 14.0 1.6 1.6 1.7 Norway 3.5 3.7 3.8 0.7 0.7 0.8 Switzerland 11.5 13.0 11.0 1.6 1.6 1.5 Turkey 90.0 93.0 101.0 1.2 1.2 1.3 Average ERMCO 391.2 359.5 349.4 0.7 0.7 0.6 Russia 40.0 41.0 44.0 0.3 0.3 0.3 USA 203.0 225.0 230.0 0.6 0.7 0.7 Japan 88.0 91.0 99.0 0.7 0.7 0.8

The demand for new construction in the U.S. has helped the readymixed concrete industry to flourish over the last several decades. Concrete production rose from 203 million cubic meters in 2011 to over 230 million

60 cubic meters in 2013. Ready-mixed concrete is one of the few building materials manufactured in close proximity to a construction site, thus minimizing the impact of transportation and contributing to the local economy. There are about 2,500 ready-mixed concrete companies operating over 7,500 concrete plants in the U.S. Companies range from small family-owned businesses with one concrete plant and several concrete trucks to large multi-national corporations with hundreds of concrete plants and thousands of concrete trucks. Together, these companies form an integral part of the nation’s economy, representing $40 billion of economic activity (NRMCA, 2009a). In the future, there will be greater focus on the impact of the readymixed concrete industry on the environment. However, in this respect, it is important to view the industry in perspective. The popularity of readymixed concrete has increased greatly over the last 20 years, such that very few construction sites in Hong Kong or Singapore, with the exception of some very large projects and projects that require small infrequent batches of concrete, still use site-mixed concrete. In China and some other countries in Asia, small batching plants employing traditional reversing drum mixers are still in operation, in addition to the old Dragline plants, which generate a considerable amount of dust. The main advantage of ready-mixed concrete is its convenience. Having a centrally positioned batching and mixing plant with trucks serving several construction sites makes sound commercial sense. The use of ready-mixed concrete is also a sensible and preferred option on congested city sites with limited space or access. In fact, this kind of concrete usually ensures a consistent product and improved safety when the producer is established and responsible (Stanley, 2007). Rapid economic development and population growth is not yet complemented by fully effective environmental regulations and conditions for the ready-mix concrete production industry. The challenges presented in this vital sector for development include the following: 1) Rapid population growth, industrialization, and real estate development have impacted the environment of the region in a harmful way. 2) There is a lack of both legislation and awareness in regard to maintaining a sustainable ready-mix concrete production process in the industrial sectors.

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3) The need for infrastructure has never been more crucial to controlling and supporting the ever-increasing amount of ready-mix concrete being produced. Best Management Practices (BMPs) for the Ready-Mix Concrete Production Process cover the following areas: raw materials handling and transport, process operation, housekeeping, waste management, emergency response, and training and record keeping. These BMPs specifically tailored for the ready-mix concrete manufacturing sector set out specific permit conditions issued for each operating ready-mix facility. For each hazard or potential release to the environment, there are one or more BMPs. Overall, BMPs can relates to physical structures, activities, practices, or procedures that prevent, reduce, or mitigate an undesired event, impact, or effect. It is important to identify which BMPs apply to which situation. It is also important to understand which BMPs are the most appropriate for a hazard or environmental release. BMPs are organized by the topic areas shown in Table 1.16. Table 1.16 Best Management Practices (BMPs) for the Ready-Mix Concrete Production Process (Kashwani et al., 2014). Topic area Best Management Practice Raw materials  All raw material storage piles should be protected handling, storage, by enclosures from the wind. Staff working with and transfer ready-mixed concrete should ensure that filters on cement silos are operating properly. Broken cement silo filters are one of the biggest problems observed at ready-mixed facilities in the Emirate. Defective cement silo filters can lead to very large amounts of particulate matter (PM) emissions. Usually, a silo that has cement dust on the top or down the silo has a filter that is not working. Process opera Use dust collection systems, such as baghouses tions and filters, to collect PM from handling and mixing operations.

62 Table 1.16 (Cont.) Best Management Practices (BMPs) for the Ready-Mix Concrete Production Process (Kashwani et al., 2014). Topic area Best Management Practice  Regularly inspect and maintain dust-collection systems and bag houses.  Minimize the number of material transfer points.  Minimize the drop heights for material transfer to/from conveyors and hoppers.  Shroud or enclose transfer points.  Refuel vehicles on impervious surfaces.  Construct a bund wall around diesel storage tanks to contain 110% of the tank volume.  Monitor noise generated from operations. Housekeeping  Maintain clean premises and ground surfaces by sweeping, shoveling, wiping, and using dust-collection vacuums.  Regularly schedule site cleanings to remove waste materials.  Provide vegetative barriers to reduce the spread of dust. Waste manage Perform truck washout activities in a concrete pit ment so that the wash water is not discharged onto the ground.  Collect, treat, and recycle washout wastewater, including concrete and cement (for example: mortar, grout, slurry), residues and contaminants, from truck and equipment washout activities.  Designate skips for solid waste materials.  Segregate hazardous and non-hazardous waste types.  Dispose of hazardous waste through an environmental service provider approved by the regulator.  Collect and reuse waste concrete from the truck washout pit.

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Table 1.16 (Cont.) Best Management Practices (BMPs) for the Ready-Mix Concrete Production Process (Kashwani et al., 2014). Topic area Best Management Practice  It is important not only to collect and remove waste, but to make sure waste is properly disposed of. Emergency  Provide spill prevention and response procedures preparedness and and provide kits to clean up spills and leaks. response  Label chemicals, and provide MSDS for each chemical.  Keep firefighting equipment properly maintained.  Provide appropriate PPE for employees.  Have an emergency response plan, train employees on emergencies, and conduct drills. Training and  Train employees in good housekeeping, spill prerecord keeping vention and control, proper fueling procedures, safety, PPE, and material management.  Conduct induction and refresher training sessions regularly.  Provide an integrated EHSMS for the site, plant operations, and delivery process.

Environmental considerations are becoming increasingly important in all industries, and the ready-mixed concrete industry is no exception. For example, emissions of cement dust are strictly controlled by the use of dustextraction systems in loading areas and cement silo filter systems, restrictions on powder-blowing pressures, and the provision of high-level silo alarm systems. In addition, many plants now have water-recycling systems, which minimize the amount of water discharged from the site. All wash-out and surface water is stored, any excess solids removed, and the water re-used in concrete. Some of the busiest plants also have complete concrete recycling units, which separate returned concrete and/or wash-out water into individual reusable components (Crompton, 2003). There are many ways to produce environmentally friendly concrete with no single solution to fit all situations.

64 Instead, a complicated evaluation is necessary in order to take into account the entire lifecycle of the concrete, including numerous parameters that are often not controlled by the concrete producer. Furthermore, nonenvironmental issues often overrule the decision. However, if a concrete manufacturer works through the check list then he is forced to address the environmental issues and to consider the need for changes, as shown in Table 1.17. This process will, overall, lead to greater awareness of environmental issues and steps to address them in the industry (fib, 2012). Table 1.17 Check List for Concrete Manufacturers. Environmental issues to be Beneficial environmental effects considered by the concrete producer Is the most efficient mode of Minimized transport impact transport being exploited? Is the mix design optimized with Reduced consumption of cement respect to packing the aggregates? clinker and reduced CO2 emissions Does the mix design include blended cement or supplementary cementitious materials as a substitute for cement clinker? If yes, are these materials residual products from other industries? Is the concrete optimized with respect to its purpose? (strength, durability, structural design) Is the concrete hydration fully utilized with respect to drying surplus moisture before finishing the work and also with respect to proper strength development? Are vegetable-based release agents used to the maximum extent? Also, vegetable-based hydraulic oils?

Reduced need to deposit industrial residual products such as ash slag, and reduced use of natural resources

General optimization of the concrete design to fit its purpose in the final building or civil structure

Bio-degradable materials and reduced risk of hydrocarbons in concrete slurry

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Table 1.17 (Cont.) Check List for Concrete Manufacturers. Environmental issues to be Beneficial environmental effects considered by the concrete producer Is wash water reused after the Minimized consumption of natural sedimentation tank? Either as resources and reduced waste mixing water or wash water. generation Is rain water used in production? Is concrete slurry from the sedimentation tank recycled? Are aggregates from the fresh concrete reclaimed? (Surplus production, rejected batches) Is hardened concrete waste crushed and recycled? (in other constructions or back into concrete) Is other waste collected and sorted for proper recycling? (paper, plastic, metal, mineral oil, chemicals, etc.) Is the working environment benefiting from the chosen concrete solution? (SCC) Have appropriate steps been taken to minimize noise and dust? Are locally available aggregates being utilized to the greatest possible extent? Is the plant equipment up-to-date and well-maintained? Is there a procedure for energy awareness and resource consumption among the employees? Is the potential of on-site/off-site renewable energy supplies being exploited?

Reduced consumption of natural aggregates and reduced need to deposit waste

Reduced need to deposit waste and reduced consumption of resources Better conditions for concrete workers both at precast factories and on building sites Improved working environment and external environment Minimized transportation Minimized energy consumption and reduced waste generation

Minimized energy use impact

66 The ready-mixed concrete industry is dedicated to upholding the principles of sustainable development—i.e., development that meets the needs of the present without compromising the ability of future generations to meet their own needs—by attempting to balance social, economic, and environmental impacts. Sustainability has become part of the fabric of society. Corporations in every industry are shaped by their customers’ desire to be more environmentally responsible. Companies that adopt sustainable practices will become preferred suppliers. Environmental performance, including greenhouse gas emissions, will be increasingly monitored and regulated. However, voluntary initiatives such as the one presented here will help achieve ambitious sustainability goals (NRMCA, 2009a). The United States Green Building Council (USGBC) will transition their Leadership in Energy and Environmental Design (LEED) rating system from LEED 1.2 to LEED 2009 as of March 1, 2009. Projects registered before March 1 will have the option of meeting the requirements of LEED 1.2 or LEED 2009, whereas projects registered after that date fall under the 2009 version. The current version of the Ready Mixed Concrete Industry LEED Reference Guide addresses the LEED 1.2 version. In partnership with the National Ready Mixed Concrete Association (NRMCA), RMC Research & Education is working to update the guide to incorporate changes into the 2009 version in regard to the use and treatment of ready-mixed concrete. The LEED 2009 NC rating system has five main credit categories: Sustainable Sites, Water Efficiency, Energy & Atmosphere, Materials & Resources, and Indoor Environmental Quality, as shown in Table 1.18. Each credit category is divided into credits and outlines the intent, requirements, technologies, and strategies for meeting each credit. Credits are broken down into individual points. Additional points can be earned for Innovation & Design Process credits and for meeting specific Regional Priority Credits (PCA, 2005).

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Table 1.18 LEED V4 Credit Categories and Points Available in Each Credit Category. Credit Category Points Available Sustainable Sites (SS)

26

Water Efficiency (WE)

10

Energy & Atmosphere (EA)

35

Materials & Resources (MR)

14

Indoor Environmental Quality (EQ)

15

Innovation & Design Process (ID)

6

Regional Priority Credits (RP)

4

Total Points Available

110

As shown in Table 1.19, in each section, the discussion of the LEED 2015 NC Credits relevant to ready-mixed concrete is separated into those issues primarily affecting project designers (Design Issues section) and those primarily affecting concrete trade professionals (Trade Contractor and Manufacturer Issues section). However, each group needs to read both portions, as both groups are often responsible for completing documentation requirements. In general, the Design Issues section addresses issues that must be decided before construction begins, whereas the Trade Contractor and Manufacturer Issues section is concerned with actual construction and close-out. A final section of the document addresses environmental considerations in regard to using ready-mixed concrete with reference to plant waste water disposal, on-site wash water disposal, solid waste, and site protection. In terms of points required for certification, a building requires at least 40 points for basic certification level. Silver level requires 50 points, gold level requires 60 points, and platinum requires 80 points. There are a total of 110 points available.

68 Table 1.19 Potential LEED Credits for Ready-Mixed Concrete (NRMCA, 2009b). Concrete contributes to this LEED Credit Incidental concrete use in this LEED Credit Sustainable Sites 26 Possible Points Prerequisite 1 Construction Activity Pollution Prevention Required Credit 1 Site Selection 1 Credit 2 Development Density and Community 5 Connectivity Credit 3 Brownfield Redevelopment 1 Credit 4.1 Alternative Transportation―Public Trans6 portation Access Credit 4.2 Alternative Transportation―Bicycle Storage 1 and Changing Rooms Credit 4.3 Alternative Transportation―Low-Emitting 3 and Fuel-Efficient Vehicles Credit 4.4 Alternative Transportation―Parking Ca2 pacity Credit 5.1 Site Development―Protect or Restore Habitat 1 Credit 5.2 Site Development―Maximize Open Space 1 Credit 6.1 Stormwater Design―Quantity Control 1 Credit 6.2 Stormwater Design―Quality Control 1 Credit 7.1 Heat Island Effect―Nonroof 1 Credit 7.2 Heat Island Effect―Roof 1 Credit 8 Light Pollution Reduction 1 Water Efficiency 10 Possible Points Prerequisite 1 Water Use Reduction Required Credit 1 Water-Efficient Landscaping 2–4 Credit 2 Innovative Wastewater Technologies 2 Credit 3 Water Use Reduction 2–4 Energy and Atmosphere 35 Possible Points

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Table 1.19 (Cont.) Potential LEED Credits for Ready-Mixed Concrete (NRMCA, 2009b). Concrete contributes to this LEED Credit Incidental concrete use in this LEED Credit Prerequisite 1 Fundamental Commissioning of Building Required Energy Systems Prerequisite 2 Minimum Energy Performance Required Prerequisite 3 Fundamental Refrigerant Management Required Credit 1 Optimize Energy Performance 1–19 Credit 2 On-site Renewable Energy 1–7 Credit 3 Enhanced Commissioning 2 Credit 4 Enhanced Refrigerant Management 2 Credit 5 Measurement and Verification 3 Credit 6 Green Power 2 Materials and Resources 14 Possible Points Prerequisite 1 Storage and Collection of Recyclables Required Credit 1.1 Building Reuse―Maintain Existing Walls, 1–3 Floors, and Roof Credit 1.2 Building Reuse―Maintain Existing Interior 1 Nonstructural Elements Credit 2 Construction Waste Management 1–2 Credit 3 Materials Reuse 1–2 Credit 4 Recycled Content 1–2 Credit 5 Regional Materials 1–2 Credit 6 Rapidly Renewable Materials 1 Credit 7 Certified Wood 1 Indoor Environmental Quality 15 Possible Points Prerequisite 1 Minimum Indoor Air Quality Performance Required Prerequisite 2 Environmental Tobacco Smoke (ETS) Required Control Credit 1 Outdoor Air Delivery Monitoring 1 Credit 2 Increase Ventilation 1

70 Table 1.19 (Cont.) Potential LEED Credits for Ready-Mixed Concrete (NRMCA, 2009b). Concrete contributes to this LEED Credit Incidental concrete use in this LEED Credit Credit 3.1 Construction Indoor Air Quality Management 1 Plan―During Construction Credit 3.2 Construction Indoor Quality Management 1 Plan―Before Occupancy Credit 4.1 Low-Emitting Materials―Adhesives and 1 Sealants Credit 4.2 Low-Emitting Materials―Paints and Coatings 1 Credit 4.3 Low-Emitting Materials―Flooring Systems 1 Credit 4.4 Low-Emitting Materials―Composite Wood 1 and Agrifiber Products Credit 5 Indoor Chemical & Pollutant Source Control 1 Credit 6.1 Controllability of Systems―Lighting 1 Credit 6.2 Controllability of Systems―Thermal Comfort 1 Credit 7.1 Thermal Comfort―Design 1 Credit 7.2 Thermal Comfort―Verification 1 Credit 8.1 Daylight and Views―Daylight 1 Credit 8.2 Daylight and Views―Views 1 Innovation and Design Process 6 Possible Points Credit 1 Innovation in Design 1–5 Credit 2 LEED-Accredited Professional 1 Regional Priority 4 Possible Points Credit 1 Regional Priority 1–4 Total Points 110 Possible Points

Obtaining a LEED certification demonstrates to the community that a company or industry is committed to the environment. Additionally, implementing green building practices can result in energy and cost savings

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over the life of the structure. Other advantages include better indoor air quality and plenty of daylight. According to research, workers in these environments show increased labor productivity, job retention, and days worked. These benefits contribute directly to a company’s profits because salaries—which are about 10 times higher than rent, utilities, and maintenance combined—are the largest expense for most companies that occupy building space (Lemay and Peng, 2014). Technologically speaking, readymixed concrete (RMC), a building material of paramount importance, undoubtedly represents an advance over site-mixed concrete. The benefits of RMC in terms of quality, speed, lifecycle cost, and environmental friendliness are overwhelmingly superior to those of site-mixed concrete. An added advantage of RMC is that the quantity of cement can be reduced by replacing a portion of the cement with supplementary cementitious materials such as ground granulated blast furnace slag (GGBS), fly ash, and microsilica, which are all industrial by-products that would otherwise become solid waste and thereby exacerbate existing environmental issues. Compared with site-mixed concrete, RMC is more durable, as better process control and monitoring of the raw materials is involved in producing the latter. The addition of supplementary green cementitious materials such as fly ash, silica fume, and GGBS reduces the perviousness in concrete, making it more durable, more sustainable—in short, a green product (Manjunatha and Anvekar, 2015). Many beautiful and award-winning developments have made great use of RMC. In its ready-mixed form, the sustainable and environmentally friendly potential of concrete can be most fully realized. With its use of locally available materials and short delivery journeys, RMC minimizes the energy use and environmental impact ordinarily associated with the distribution of products. RMC also has the ability to aid in the use of suitable industrial by-products and similar waste materials, thereby reducing the amount of waste that must be disposed of. Furthermore, inert recycled demolition material can be used in the aggregate for RMC. In this way, buildings and other structures made from RMC are highly adaptable and can be metamorphosed time and again throughout their long lifespans. The durability of RMC, the local aspect of its production and use, and the recyclability of RMC in both its fresh and hardened stages together with all the

72 other environmental benefits it offers mean that RMC can reasonably be described as ―a natural choice‖ (ERMCO, 2000). Based on this description, the promotion of RMC green production has become necessary to efforts to accelerate the creation of a resource-conserving and environmentfriendly society. RMC green production means that maximum utilization of resources and minimum environmental pollution is achieved and the occupational environment of plants is improved through product selection, design, production, supply management, and product evaluation in concert with considerations pertaining to resource conservation, environmental protection, and occupational health (Wu, 2014).

1.8 Green concrete as a repair material Concrete has been in service as a structural material for centuries. In its massive form, when used to resist essentially compressive loads, it is a reliable and durable material provided that precautions are taken to resist sulphate attacks by ground water and freeze-thaw effects. The possibility of alkali-silica must also be recognized. It is unfortunate that concrete must be reinforced with embedded metal when used to resist the tension of flexural loading. It is this embedded metal’s susceptibility to corrosion that is the prime cause of the majority of structural concrete deterioration, as is now becoming evident. Each year, concrete is repaired at considerable expense. It is important, therefore, that the construction industry recognizes the errors of the past and puts to good effect in new construction lessons learned. Buildings and other structures must be designed and financed with a planned maintenance program in mind, and when repairs become necessary their performance must be subsequently monitored (Mays, 2003). Infrastructure ages and maintenance isn’t always proactive; therefore, the need for concrete repair is growing. Making repairs is typically more sustainable than replacing an entire structure. However, key steps can be taken in the repair process to minimize environmental impact (Concrete Joint Sustainability Initiative, 2015).

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1) Condition evaluation: The first important step is to have a licensed professional engineer conduct a comprehensive condition evaluation to identify the cause(s) and degree of deterioration or damage. To design a durable repair, it is important to understand the specific deterioration mechanisms that affect a structure. 2) Lifecycle cost analysis: Based on anticipating maintenance and repair requirements over an extended period of time, an optimal maintenance and repair plan can be devised following the condition evaluation. 3) Repair design: A repair approach should salvage as much concrete as possible while achieving durability. For this to happen, the repairs should include appropriate measures to control reinforcing steel corrosion in both the parent concrete and in the repairs. 4) Waste management: A plan should be devised and implemented to deal with waste from the portions of the structure that must be removed as well as the packaging in which new materials were delivered. Where possible, the removed materials should be recycled, or preferably reused, instead of sent to landfills. Similarly, new materials should be shipped with minimal packaging, which should be reusable and/or recyclable. 5) Use green repair materials: Once selected, the repair approach should be implemented using repair materials that will minimize negative environmental impact. 6) Successful repair implementation: Even with an optimal design and green materials, a repair project should be implemented properly to minimize its environmental impact. Repairs should be carried out by a contractor in accord with a comprehensive quality control plan. 7) Future monitoring: Once repairs are completed, it is important to monitor the condition of the structure to determine when preventative maintenance or subsequent repairs will be required. This is typically achieved through periodic evaluations of the structure’s condition. Embedded sensors and data-acquisition systems can also be used to continuously monitor certain performance parameters (such as corrosion activity, chloride contamination, water leakage, temperature, structural deformations, and cracking).

74 Edvardsen and Tølløse (2001) presented some design and green maintenance and repair strategies. One important purpose of their project is to elaborate various maintenance/repair strategies based on alternative designs. Two main design principles reflect different maintenance/repair strategies (other intermediate solutions possible), see Table 1.20: Table 1.20 Various Green Design Principles and Maintenance/Repair. Design principle Construction stage Maintenance/repair stage 1 Cheap Expensive 2 Expensive Cheap

1) The first design principle assumes the construction of a cheap, not very robust, and not very durable structure that requires repeated, environmentally and financially speaking, extensive maintenance/ repairs. For example, the structure might have limited concrete cover and low construction costs, but may bring substantial repair costs due to the deterioration of concrete caused by corrosion of the reinforcement at an early stage. 2) The second design principle assumes the construction of an expensive, robust, durable structure that requires minimum maintenance/ repair and is environmentally and cost friendly. For example, a structure made with stainless steel instead of traditional black reinforcement such that there is almost no need for maintenance/repair during the entire service life. The choice of material and technique is governed in the first instance by the scale of the proposed repair. The first consideration is the choice between resin-based and cementitious materials. As indicated, the development of cementitious materials has reached the stage that these should be the first choice, unless there are factors that preclude them. An outcome of the intensive activity in developing cementitious repair materials is the appearance on the market of complete ―repair packages‖ from most of the specialist formulators. These usually include not only a fairly sophisticated repair mortar but also a bond coat or bonding bridge to promote good adhesion

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between the repair mortar and the concrete substrate, an anti-corrosion primer for the steel reinforcement and an anti-carbonation coating to apply over the entire structure after a repair (Mays, 2003). Use green repair materials, Once a repair approach has been selected, it is important to implement it using repair materials that will minimize the negative environmental impact. Factors that should be considered include: • Recycled content • Locally sourced content • Volatile organic compound (VOC) content • Durability • Service life • Packaging • Recyclability • Ease of use (lowers probability of premature failure) • Embodied energy • Mixing and application method • Greenhouse gas emissions from manufacturing and transport • Hazardous components such as heavy metals • Impact on heat island effect (solar reflectance and emissivity) With LEED certification of buildings becoming more mainstream, many manufacturers have started to document readily available information supporting the green aspects of their product lines. This readily available information usually only scratches the surface of the sustainability of their products, however, such that manufacturers must usually provide additional information about the sustainability of their products (ICRI, 2015). Reactive powder concrete (RPC) is also being used as a new repair material given its bond durability to existing concrete. RPC has excellent repair and retrofit potential in regard to compressive and flexure strengthening and has high bond strength, dynamic modulus, and bond durability as compared with other concretes. The adhesion between RPC and steel is also much greater than that for other concretes. It would be interesting to verify the consequences of this improved adhesion and repair in reinforced concrete structures (Lee et al., 2007). Yunsheng et al. (2008) investigated a new type of Green Reactive Powder Concrete (GRPC) with compressive strength of

76 200 MPa (C200 GRPC) prepared by utilizing composite mineral admixtures, natural fine aggregates, and short and fine steel fibers. The experimental results show that the mechanical properties of other kinds of concrete are inferior to those of C200 GRPC made with cementitious materials consisting of 40% Portland cement, 25% ultrafine slag, 25% ultrafine fly ash, 10% silica fume, and 4% volume fraction of steel fiber. The corresponding compressive strength, flexural strength, fracture energy, and fiber–matrix interfacial bonding strength are more than 200 MPa, 60 MPa, 30,000 J/m2, and 14 MPa, respectively. The dynamic tensile behavior of the C200 GRPC has also been investigated through the Split Hopkinson Pressure Bar (SHPB) according to the spalling phenomenon. The dynamic testing results demonstrate that the strain rate has an important effect on the dynamic tensile behavior of C200 GRPC. With an increase in the strain rate, the peak stress rapidly increases in the dynamic tensile stress–time curves. The excellent static and dynamic properties of GPRC are mainly ascribed to two aspects: The first aspect is the ultrafine steel fiber, this greatly improves the GRPC’s mechanical strength, fracture energy, and interfacial bonding strength. The second aspect is attributed to the particle packing and filling effect and the pozzolanic effect and micro-aggregate effect of the composite mineral admixtures, which result in a very compacted GRPC matrix with low porosity and few macro-defects. These effects further improve with the development of curing ages under the standard curing regime. Polymers in concrete have received considerable attention over the past 25 years. Polymer-impregnated concrete (PIC) was the first concrete polymer composite to receive widespread publicity. Yet, even though PIC has excellent strength and durability properties, it has few commercial applications. Polymer concrete (PC) became well known in the 1970s and is used for repair, thin overlays for floors and bridges, and for precast components. Polymer-modified concrete (PMC) is used primarily for repair and overlays. However, several limitations have restricted the use of concrete polymer materials. That said, there are many current and future uses for these materials that will use their unique properties to good effect. Improved, automated repair methods, improvements in materials, replacements for metals, structural applications, and architectural components are expected to be popular uses of concrete-polymer materials eventually (Fowler, 1999).

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Similarly, polymer mortar (PM) is a composite material formed from a resin binder and fine inorganic aggregates such as sand and fly ash. The resulting product is a strong, durable material typically used as a protective coating in various Portland cement concrete structures. Another important advantage of PM is its fast curing time: it cures in a few minutes or hours whereas cement-based materials cure in a few days or weeks. Rebeiz et al. (1994) studied the important properties and behavior of PM materials made with unsaturated polyester resins based on recycled poly (ethylene terephthalate, PET) and plastic waste. The recycled PET is mainly recovered from used plastic beverage bottles collected in many localities. Finally, as a revolutionary construction material, ultra-high performance concrete (UHPC) has been extensively studied in the last two decades, and one line of research has focused on preparing UHPC with low-priced raw materials or industrial by-products. In a study by Zhao and Sun (2014), a green UHPC including high volumes of fly ash and river sand as part of the raw materials was prepared, and the objective was to investigate the nanomechanical behavior of the UHPC using nanoindentation. The results show that the hydration products, which account for about half the paste by volume, are mainly high-stiffness hydrate phases and that significant quantities of unreacted cement and fly ash have higher mechanical properties than the hydration products do and can function as micro-aggregates to strengthen the UHPC paste. Moreover, the mechanical properties of the paste near the aggregate or fiber surfaces are similar to those of the bulk paste, which indicates that the UHPC has a strong and efficient bond at the interfacial zone. The experimental findings at the nano-scale provide a basis for understanding the macro-performance of green UHPC (Zhao and Sun, 2014). Sustainable industrial growth will influence the cement and concrete industry in many respects, as the construction industry has a large environmental impact due to its high consumption of energy and other resources. One important goal is the use of environmentally friendly concrete to enable worldwide infrastructure growth without an increase in CO2 emissions. Another, probably even more important, goal is the use of more environmentally friendly structural designs incorporating more environmentally friendly maintenance/repair strategies that require fewer resources and

78 reduce the energy used and the CO2 emissions at every stage of the service life of a concrete structure (Edvardsen & Tølløse, 2001).

1.9 Conclusion In this chapter, we described perspectives on the uses and potential uses of concrete as a green material, guidelines for green concrete, green cement production, the use of recycled materials in concrete, green cement and concrete composites and green concrete as a repair material. Related to cleaner technologies for the production of concrete, the major targets are achieving (a) a significant reduction in CO2 emissions, (b) a significant reduction in energy consumption and fossil fuel in the cement-manufacturing process, (c) a significant reduction in the use of substances that endanger health and/or the environment, such as several types of chemicals commonly used in concrete mixtures, (d) significant savings associated with the use of cement by partially replacing it with fly ash waste and/or other kinds of waste materials, (e) a significant increase in the use of new cement replacement materials, such as inorganic polymers, alkali-activated cement, magnesia cement, and sulfoaluminate cement, and (f) significant development of various possibilities relevant to recycling cement/concrete and the use of alternative aggregates. Other significant contributions are establishing and extending policies or regulations set out by various countries, institutions, and industries and promoting the willingness of the community to use green concrete. Even owners and developers have discovered that ―going green‖ is not only accepted now as politically correct and as a source of intangible benefits and good publicity, but that also it is a way to improve their bottom line. Moreover, the idea that green buildings are of lower quality than standard buildings is losing ground fast. Rating systems such as LEED are expected to become the norm in the very near future, and material suppliers such as concrete producers will be pressed to compete on the basis of environmentally friendly principles, i.e., in terms of energy consumption, lifecycle costs, and recycled materials. There is reason to believe that the concrete industry is well positioned for success, given the tools outlined

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herein. Finally, green materials can be used to produce high-performance cement and concrete. Concrete must keep evolving to satisfy the increasing demands of all its users. Designing for sustainability means accounting for the short-term and long-term environmental consequences in the design.

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