INTEGRATED ENVIRONMENTAL DESIGN AND OPTIMIZATION OF ...

The 2005 World Sustainable Building Conference, Tokyo, 27-29 September 2005 (SB05Tokyo)

02-029

INTEGRATED ENVIRONMENTAL DESIGN AND OPTIMIZATION OF CONCRETE FLOOR STRUCTURES FOR BUILDINGS

Petr HAJEK Department of Building Structures, Czech Technical University in Prague, Faculty of Civil Engineering, Thakurova 7, 166 29 Prague 6, Czech Republic, [email protected]

Keywords: integrated design, optimization, environmental performance, recycled waste, RC floor slabs

Summary Integrated environmental design represents a new approach integrating material, structural and environmental aspects in one complex design and optimization process. The target goal is reduction of negative environmental impacts, while increasing the structure’s serviceability, durability and reliability throughout its entire expected life. This should be achieved while keeping the cost on reasonable (minimum) level and performance at a feasible (maximum) level. A theoretical and practical approach to environmentbased integrated design and optimization of concrete structures is presented. The concept of integrated design and optimization is shown and proved on the two cases of RC floor structures with lightening fillers from recycled waste plastics. These optimized solutions have been approved by realizations in situ. The analysis showed that using recycled waste plastics and the optimized shape of shell fillers, it was possible to reduce consumption of non-renewable silicate materials, the resulting embodied CO2, SO2 .... and primary energy consumption. Moreover, due to the new structural concept the functionality and overall performance quality have been increased.

1.

Backgroung

The traditional approach to design of structures has commonly been aimed at achieving the required utility characteristics, while maintaining acceptably low financial costs of construction. The time interval usually applied for the assessment of the solution efficiency has been limited to the construction stage, or to a period of a few years following after the construction completion. In contrast, the new conceptual approach to design of structures is an integrated design. The basic methodology of integrated design was described by Sarja (2002). It represents a multi-parametric design approach viewing various definition levels (material, components, structure) and aimed to achieve optimum function parameters as seen from a wide spectrum of criteria throughout the entire life cycle. The innovative approach is based on the design of the structural material and component with functional characteristics defined in advance so that they can meet functional demands resulting from the anticipated performance of the material and component in a specific structure during the whole life cycle. In other words, the design should involve optimization of all components in all major phases of the life cycle (from the construction till the demolition of the structure). The condition for achieving these parameters is integration of various design components, including material, structural, and environmental ones, into a single design process. At the same time, further sustainable development criteria should be respected, comprising economic and sociocultural ones. The environmentally based optimization of the RC floor structure, including verification of suitability of using recycled waste materials, was one of the key research topics in the frame of research project performed at the CTU in Prague in 1998-2001. The possibility of the use of recycled industrial and/or municipal waste for production of light fillers for waffle or ribbed RC floor slabs was analysed. The results of the research proved the acceptability of replacement of silicate fillers by fillers from recycled waste materials. Two alternatives of lightening fillers from recycled non-sorted waste plastic (waffle shell fillers for RC slabs and installation shell fillers for composite RC "filigran" slabs) were experimentally produced in recycling company Transform Lazne Bohdanec and tested at CTU from structural as well as hygienic point of views. Some results have been already presented by Hajek and Wasserbauer (2002) on Sustainable Building 2002 Conference in Oslo.

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2.

Principles of Integrated Environmental Design and Optimization

Integrated design is a new approach implementing all relevant and significant requirements into one single design process. This approach integrates material, component, and structure design and considers selected relevant criterions from a wide range of criterions sorted in four basic groups: environmental, economical, technical and socio-cultural. The target instruments have a multicriterial nature and involve many different criterions like functional quality, costs, environmental impact, durability, reliability and other. The decisive methodological approaches of integrated design include multicriterial optimization of function parameters, and sensitivity and risk analysis. The requirement that behaviour should be predicted for the whole life cycle leads to application of the probability approach. The new conceptual 3D model of an integrated design, representing time dependent multi-parametric design has been proposed by Hajek (2004) and its application on concrete structure design is being developed within the work of fib Commission C3 – Task Group C3.7 Integrated Life Cycle Assessment of Concrete Structure. This approach considers: •

different performance criteria (environmental criteria, economic criteria, technical quality criteria and socio-cultural criteria)

•

sequential life phases of the structure throughout the entire life cycle

•

various definition (recognition) levels (material, components, entire structure)

life cycle phases

z

criteria y

level

recognition

reco leve

The principle of the three dimensional complex model is shown in the Figure 1. On the horizontal x-axis are selected groups of performance criterions, on horizontal y-axis are life cycle phases and on vertical z-axis are different definition levels.

material

Figure 1

socio cultural aspects

technical quality

component

economic criteria

structure

environmental criteria

performance criteria x

recycling demolition reconstruction maintenance operation construction production structural design conceptual approach

Conceptual 3D model of integrated design

Life Cycle Phases Integration (y – axis): The conceptual model for integrated life-cycle design is based on LCA principles (according to EN ISO 14040). Total impact value Itot associated with particular criterion can be expressed as a sum of partial impacts Ii as follows Itot = ∑ Ii

(1)

where Itot represents total impact of criterion within the entire life and Ii is partial impact corresponding to particular life phase. Performance criterions integration (x – axis) is based on a complex consideration of a set of relevant and significant criterions. This needs application of multiparametric assessment tools usually based on weighting procedure. Ii = ∑ wj Qj

(2)

T

where {wj} = (w1 ... wm) is the vector of weights representing importance of individual criteria, m is the number of essential criteria and {Qj} = (Q1 ... Qm)T is the vector of embodied values of criteria. The assessment and/or optimization process on one definition level could be formalized by following equation: ItotR = ∑∑ wj Qj

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(3)


Definition (recognition) levels integration (z – axis) is based on parallel application of multicriterion LCA design tools on corresponding definition levels. The permanent interaction in the interface between parallel levels is considered. The complex 3D model can be expressed by the formal scheme shown in the Figure 2.

structure level

ItotIII = ∑∑ wj Qj interface

component level

ItotII = ∑∑ wj Qj interface

material level

Figure 2

3.

ItotI = ∑∑ wj Qj

Scheme representing complex 3D analysis procedure on integrated design model

Integrated Environmental Design of Concrete Slabs – Application in Practice

The application of principles of the integrated environmental design and optimization is shown on development of the two types of RC floor slabs with fillers from recycled waste plastic for the use in construction of buildings. 3.1

Process of Design and Optimization

Material level One of the basic principles of sustainable development is a need for significant reduction of primary nonrenewable materials. The required balance in the consumption of natural materials can be searched in the form of closed material cycles, based on recycling of wastes which originate from previous cycles. There is a high potential for the use of secondary materials obtained from recycling of waste generated by other industrial processes and from municipal waste. The most of plastic waste is still as a part of mixed municipal waste incinerated with all consequential negative environmental impacts. However, separated plastic municipal waste (collected in yellow collecting containers) can be recycled in relatively simple way. The pre-sorted plastic waste is processed by crushing and grinding and resulting fractions then serve for preparation of mixtures in proportions ensuring good workability guarantying high quality of products. The mixture is subsequently homogenized, melted and squeezed into iron moulds where products receive the final shape. Elaborateness and energetic demands are not high. Processing of 1kg of plastic material needs only approximately 0.6 kW of electric energy. There are no danger environmental outputs from production - no danger waste material, waste water or harmful emissions of such a kind to endanger surrounding environment. In both developed alternatives of RC floor slabs were used shell lightening filler elements from recycled non sorted plastics from municipal waste. The possibility of the production of filler elements has been proved by experimental production of fillers in recycling company Transform Lazne Bohdanec in 1999 – 2000. Component level The shapes of fillers were determined as a result of integrated environmental design and optimization considering environmental criterions as well as structural parameters of the resulting composite structure. The optimized shapes of both alternatives are shown in the Figure 3. The initial optimization steps, covering the use of the ribbed or waffle shape and use of recycled materials, resulted in the reduction of embodied values (CO2, SO2, energy). The cut in consumption of natural (non-renewable) sources (limestone, granite, oil, etc.) is evident. Integrated performance approach is also presented by light shell elements from recycled waste plastics which create installation space for wiring and other building services inside "filigran" composite RC slabs. Structure level The two types of optimized RC composite slabs lightened by different types of fillers from recycled waste plastics were developed and used in practice. The first application in practice was construction of Senior

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Centre in Moravany in 2000, where RC floor slabs with installation shell fillers were used. The second in site application was reconstruction of the floor structure in the two storey factory hall in 2004. installation filler from recycled plastic

input to installation space

cast in situ concrete

•

•

•

RC panel – type „filligran“

installation space

lower ceiling

A

waffle filler from recycled plastic

B

Figure 3 Two types of optimized RC floor structures with lightening fillers from recycled waste plastic – A – composite RC floor slab with installation shell fillers; B - RC waffle structure with permanent shell fillers

3.2

Construction of Senior Centre in Moravany

The experimental production of installation shell fillers from recycled waste plastic sorted from municipal waste has started in spring 2000 in recycling company TRANSORM Lazne Bohdanec. These installation fillers were used within the construction of two storey building of Senior Centre in Moravany near by Pardubice in the Czech Republic. Original design of floor structure was composite RC slab. Use of shell installation fillers resulted in reduction of concrete2 consumption up to 0,08 m3 per m2 , i.e. 34%. Self weight of the floor structure was reduced about 2,0 kN/m . Installation space inside floor structure has been used for wiring and for heating system in plastic tubes. This brought additional cost savings comparing to originally assumed installation system to be placed in upper layers - inside flooring.

Figure 4

3.3

Composite filligran slab with installation shell fillers from recycled waste plastics – construction of Senior Centre Moravany

Reconstruction of the Floor Structure in the two Storey Factory Hall

Within the reconstruction of two storeys RC factory hall into a storage hall there was a requirement to increase a load bearing capacity of intermediate floor structure so that the new structure enables new function with higher live load of 5 kN/m2. Existing cast-in-place RC slab with thickness of 120 mm didn’t meet such requirements; moreover there were a lot of openings not suitable for the new way of use. Removal of the inconvenient RC floor slab was due to the time span, technological demands and total costs unfavourable. In principle this alternative would represent almost complete demolition of existing structure. The optimization analysis showed that more favourable solution would be construction of a new load bearing floor structure dimensioned to required load and covering the old openings.

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With respect to the limited load bearing capacity of existing vertical load bearing RC structure the originally expected alternative (solid full RC slab) would require increase of load bearing capacity of footings and vertical load bearing structures consisting of RC columns. Thus specific solution was requested to lighten the floor slab comparing to solid one. That’s why the alternative of waffle RC slab with fillers from recycled plastic was chosen as an optimal from technical, economic and as well as environmental point of view. New RC waffle floor slab was realized directly on the existing floor structure. Plastic fillers were placed on the floor so that the existing RC floor structure provides sufficient fire safety. In the old openings there was necessary to use protective RC slab ceiling with thickness of 80 mm reinforced with steel mesh. The load bearing RC waffle floor slab with the thickness of 250 mm was made from concrete B30 and reinforced with steel 10 425, concrete cover of 20 mm. Plastic formwork fillers were made as a custom manufacturing in TRANSFORM Lázně Bohdaneč company between October and November 2003 in total amount of 650 m2 of the fillers. The construction was realized between December 2003 and January 2004 without any technological problems.

Figure 5

4.

Waffle RC slab with shell fillers from recycled waste plastics – reconstruction of factory hall

Evaluation of Environmental Impacts

Some previously performed LCA analyses showed that using recycled materials and the optimized shape of the floor structure, it was possible to reduce environmental impacts such as consumption of non-renewable silicate materials, the resulting level of embodied CO2, embodied SO2 and embodied energy. Some results of previous LCA analyses have been already presented by Hajek (2003) and are also available on www.substance.cz or on author's webpages. In the Figure 6 is presented comparison of environmental profiles of both optimized floor slab structures with fillers from recycled non-sorted plastic in relation to reference level represented by RC full slab (100%). The reduction of embodied CO2 is 27 – 32%, reduction of embodied SO2 20 – 24%, reduction of embodied energy around 12%.

72,8 67,9

embodied CO2

79,3 75,9

embodied SO2 primary material use

55,5

63,3 67,2 65,0

self weight 0

25

50

75

100% = RC slab

87,4 87,9

embodied energy

100 %

composite RC slab with filigran panel and installation fillers from recycled plastic waffle RC slab with fillers from recycled plastic

Figure 6

Environmental profiles of optimized RC floor slabs with fillers from recycled plastic

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In the Figure 7 there is a comparison of input material flows (during construction) and output flows (during demolition). It shows that optimized alternatives use les of primary material on one side and more recycled materials on the other side. However, the amount of primary material use and materials with expected downcycling process after demolition is still very high. This is due to the fact, that concrete is nowadays mainly produced from primary materials and demolished concrete is usually used just for products with lowered quality/performance. These proportions could/should be in the future changed with respect to the current fast development of recycling techniques. Tamura et. al. (2002) show importance and possibilities of complete recycling of concrete in the future. 600,0

kg/m

600,0 2

400,0

400,0

200,0

200,0

0,0 RC tw o-w ay slab

A

RC w affle slab Composite RC w ith fillers from slab w ith recycled pastic instalation fillers

0,0

renewable materials use

RC tw o-w ay slab

B

recycled materials use

RC w affle slab Composite RC w ith fillers from slab w ith recycled pastic instalation fillers

non-recycleable waste down-cycling

primary material use

fully recycleable material

Figure 7 Material flows during construction (A) and demolition (B) phases of entire life cycle of optimized floor structures

5.

Conclusion

Integrated environmental design represents an advanced approach integrating different aspects in one complex design and optimization procedure. There is a good chance to achieve a significant reduction of environmental impact and, simultaneously, an increase in structural reliability and safety by the complex consideration of different sets of performance criterions within the whole life cycle of the structure and on parallel definition levels (material, component, structure) while considering interaction in interfaces among them. The concept of integrated design and optimization has been shown and proved on the two cases of floor structure design. These cases of realization in situ showed the significance of the selection of materials (including recycled materials) and optimization of the structural shape. Using recycled waste plastics and the optimized shape of shell fillers, it was possible to reduce consumption of non-renewable silicate materials, the resulting production of CO2, SO2 and energy consumption.

Acknowledges The current research and the paper were supported by the grant GACR 103/05/0292. All support is gratefully acknowledged.

References Hajek, P, Wasserbauer R. 2002, Sustainability through Optimised Structures Using Recycled Waste, Proc., CD, Sustainable building 2002 conference, Oslo Hajek, P. 2003, Integrated Environmental Design and Optimization of Concrete Slabs, Proc., 21st CIA Confer. Concrete in the third millennium, Brisbane Hajek, P. 2004, Integrated Life Cycle Assessment of Concrete Structures, fib State of art report, draft Oct04, Prague Sarja, A. 2002, Integrated Life Cycle Design of Structures, 1st ed. London: Spon Press, ISBN 0-415-25235-0 Tamura, M., Noguchi T. and Tomosawa F. 2002, Life Cycle Design based on Complete Recycling of Concrete, Proc. of the 1st fib Congress Concree Structures in the 21st Century, pp 10/3-4

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