SCIENCE CHINA Technological Sciences • Review •
April 2015 Vol.58 No.4: 587–599 doi: 10.1007/s11431-015-5769-4
Ultrahigh performance concrete–properties, applications and perspectives GU ChunPing1,2, YE Guang2 & SUN Wei1,3,4* 1
2
School of Materials Science & Engineering, Southeast University, Nanjing 211189, China; Microlab, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft 2628 CN, the Netherlands; 3 Jiangsu Key Laboratory of Construction Materials, Nanjing 211189, China; 4 Collaborative Innovation Center for Advanced Civil Engineering Materials, Nanjing 211189, China Received May 15, 2014; accepted January 6, 2015
Over the last twenty years, remarkable advances have taken place in the research and application of ultra-high performance concrete (UHPC), which exhibits outstanding mechanical properties and excellent durability. It has shown great potential for the next generation infrastructure construction from the sustainability point of view. This paper will give an overview on UHPC, with particular focus on the properties, applications and perspectives. After several decades of development, several types of commercial UHPC materials are available in the market, and the properties of UHPC have been characterized by numerous experimental and field tests. Generally speaking, the performance (e.g. mechanical properties and durability) of UHPC is much better than normal concrete (NC) and high performance concrete (HPC). Therefore, the uses of UHPC are growing all over the world, in both fields of new construction and retrofitting. Nevertheless, it is still a special material and technology, which is not worldwide accepted. So some application prospects of UHPC are briefly introduced in the paper, and the efforts, which have to be made to turn UHPC into a widespread ‘regular’ technology, are discussed. This paper aims to help designers, engineers, architects and infrastructure owners to know the capacities of UHPC and thus to increase the applications of this material. UHPC, characteristics, durability, applications, perspectives Citation:
Gu C P, Ye G, Sun W. Ultrahigh performance concrete–properties, applications and perspectives. Sci China Tech Sci, 2015, 58: 587599, doi: 10.1007/s11431-015-5769-4
1 Introduction Within the last several decades amazing progress has been made in concrete technology. One of the breakthroughs is the development of ultra-high performance concrete (UHPC) with compressive strength more than 150 MPa and a remarkable increase in durability even compared with highperformance concrete (HPC). The excellent performance of UHPC makes itself a high potential material for sustainable
*Corresponding author (email:
[email protected]) © Science China Press and Springer-Verlag Berlin Heidelberg 2015
and economical applications in various structures. It is strongly believed that UHPC is well suited for the next generation infrastructure construction. The applications of UHPC are increasing in the recent years in Europe, North America, Japan, Korea and Australia. While, in some other countries, such as China, only limited applications were realized. In order to encourage the use of UHPC, it is of great significance to make UHPC to be known and accepted by more people. In this paper a general introduction on UHPC is provided. The latest information on the definition, development, composition, microstructure, general characteristics, durability and some applications of tech.scichina.com link.springer.com
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UHPC is summarized. The perspectives on the development of UHPC are also discussed.
2 Definition and development of UHPC UHPC is a new generation of cementitious material with very high strength, ductility and durability. According to AFGC (French Association for Civil Engineering) recommendations [1], it is defined as a concrete with a characteristic compressive strength between 150 and 250 MPa. (Steel) fibers are added in order to achieve the ductile behavior under tension, and if possible, to dispense with the use of conventional active or passive reinforcement. Generally speaking, the development of UHPC could be divided into four stages in terms of time, i.e. before 1980s; 1980s; 1990s and after 2000. Before 1980s, because of the lack of the advanced technologies, UHPC could only be prepared in the lab with some special methods, such as vacuum mixing and heat curing. At that time, researchers tried different kinds of methods to make the concrete denser and more compact, so that the strength of concrete could be improved. It was reported that the concrete with compressive strength up to 510 MPa could be prepared with vacuum mixing and high temperature curing [2]. Although very high compressive strength could be achieved, the preparation of UHPC was very difficult and energy-consuming at that time. In the early 1980s, the micro-defect-free cement (MDF) was invented [3]. It is a type of cement paste prepared with cement and special polymers, using a very low water to cement ratio (w/c). The design principle of MDF is to remove all the defects in the cement paste. The compressive strength of MDP could exceed 200 MPa. But, because of the expensive raw material and complicated preparation process, this material only has very few applications. In spite that MDF had drawbacks, its design principle was passed along. After the invention of MDF, DSP material (densified system containing homogeneously arranged ultrafine particles) was prepared in Denmark by Bache [4]. The defects in DSP were reduced by improving the particle parking density. Superplasticizers and micro-silica were used in this material, along with the heat and pressure curing. The maximum compressive strength of DSP could be up to 345 MPa. With the increasing compressive strength, the concrete becomes more brittle, which is the major problem for concrete with high strength. Hence, steel fibers began to be used for preparing UHPC in the 1980s. Two good examples are compact reinforced concrete (CRC) and slurry infiltrated fiber concrete (SIFCON), which occurred after DSP, and reinforced with high volume of steel fibers. Both CRC and SIFCON exhibit excellent mechanical properties and durability. However, due to the lack of effective superplasticizers, they both have workability problems. So they are very difficult to be used for in-situ concrete construc-
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tions. Only few cases of practical applications of CRC and SIFCON were reported, and they were only used for part of structures, such as balconies and staircases. Full-scale structural use of these materials was not realized. To sum up, in this period, the particle parking theory was firstly used for UHPC design, and silica fume (SF) and steel fibers began to be added in UHPC. But UHPCs in this stage all have their own problems, e.g. workability issues, so their applications are limited. In the 1990s, reactive powder concrete (RPC) was developed [5], which is a major milestone for the development of UHPC. RPC is composed of very fine powders (cement, sand, quartz powder and silica fume), steel fibers and superplasticizer. The coarse aggregates are eliminated for enhancing the homogeneity of the matrix. By optimizing the granular packing of the dry fine powders, the compact density of RPC could be improved, which gives RPC ultra-high strength and durability. The compressive strength of RPC ranges from 200 MPa to 800 MPa. It has to be noted that, thanks to the development of superplasticizers, RPC shows very excellent workability, which is an essential requirement for the large-scale applications of cement-based materials. This is RPC’s most important advantage compared with previous UHPCs. In the late 1990s, the first marketed UHPC, which was named Ductal®, was developed based on the RPC technology. After that, another marketed UHPC, BSI/Ceracem® concrete, was developed by group Eiffage and Sika. In 1997, the world’s first RPC structure, the Sherbrooke Bridge in Canada, was built. It was the first time that RPC had been used for building a whole structure. However, at that time, because of the high material cost, the applications of RPC were still scarce. In addition, the heat curing and the milling of quartz sand were very energy-consuming, which also limited the applications of RPC. So generally speaking, in the 1990s, RPC was invented and resulted in commercial UHPCs. Moreover, the first RPC bridge was built. But all these achievements didn’t lead to wide applications of UHPC because of high material cost and energy consumption. From the 2000s, much progress has been made on the development of UHPC. Thanks to the progress in mineral binder technology and increased availability of highly effective superplasticizers, to prepare and produce UHPC is no longer a problem. General characteristics and durability of UHPC also have been widely studied. With the help of advanced material analysis technologies, the hydration process and microstructure development of UHPC also have been revealed to some extent. Many researchers have proposed numerous formulations for preparing UHPCs. The researchers’ efforts were focused on reducing the material cost and improving the sustainability of UHPC. Now, UHPC can be prepared with a relatively low material cost and energy consumption. Supplementary cementitious materials, such as fly ash (FA), slag and silica fume (SF), can be used for replacing part of cement, which could reduce
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the usage of cement. Furthermore, UHPC can be prepared with normal temperature curing now. Because of the emergence of environmental friendly UHPC with relatively low cost, the applications of UHPC are increasing constantly. From the 2000s, several countries have engaged in the application of UHPC. In France, a lot of outstanding structures (bridges, facades, slabs…) have been built with UHPC [6]. UHPC also has growing applications in maintenance and development of US highway infrastructures [7]. In Australia, a significant activity was developed based on the realization of bridge structures [8]. In Switzerland, UHPC has been mostly applied to in-situ reinforcement of structures [9]. UHPC bridges have been built in the Netherlands and Spain [10,11]. Prototype bridges and structures have been built in Canada, Germany, Austria, Japan and Korea [7]. In China, UHPC has been used for producing cover plates, which are designed for covering the cable trenches along the high speed railways [12]. With the growing applications of UHPC, a wide range of different formulations are available and can be adjusted to meet the individual needs of increasing number of different applications [13]. Delightful achievements have been made on the application of UHPC, but there are still barriers that impede the wider applications of UHPC. Further discussions on the barriers will be given in Section 7.
3 Composition and microstructure of UHPC 3.1
Composition
After several decades of development, one of the most popular approaches to prepare UHPC is: High quality cement + supplementary cementitious materials + low w/c or water to binder ratio (w/b) + fine aggregates + superplasticizer + steel (or organic) fibers. The key principle is to improve the homogeneity and packing density of the mixture. The homogeneity of the mixture could be improved by eliminating the coarse aggregates, which results in a more uniform stress distribution when loaded. The packing density could Table 1
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be maximized by optimizing the particle size distribution of raw materials. Thus, smaller particles could fill the voids between the bigger particles. Due to the low w/b and the pozzolanic reaction of supplementary cementitious materials (especially SF), UHPC could attain a very dense microstructure and thus excellent performance. The addition of steel fibers helps to improve both the tensile strength and ductility of UHPC. Tuan [14] compared the composition and properties of normal strength concrete (NSC), high strength concrete (HSC) and UHPC. Details are shown in Table 1. Normally, UHPC has higher cement content, lower w/b and no coarse aggregate. Depending on the specific application, coarse aggregates are sometimes used, as well as a variety of chemical and mineral admixtures. The initial cost of UHPC far exceeds that of conventional concrete. Consequently, great efforts have been made on minimizing material costs without sacrificing the beneficial properties of UHPC. Through careful selection of the raw materials, it was possible to produce UHPC with outstanding performance and moderate material costs. The possibility of replacing SF in UHPC with metakaolin, pulverized FA, limestone microfiller, siliceous microfiller, micronized phonolith, or rice husk ash (RHA) has been investigated [14–16]. Several researches have shown that fine ground quartz sand could be replaced by well-graded natural sand with a maximum size of 2–8 mm [12,17]. With the growing concern on the concept of sustainability, supplementary cementitious materials, such as FA and slag, have been widely used to partially replace cement when preparing UHPC. The volume fraction of steel fiber also could be reduced if UHPC is reinforced with conventional steel rebar. It can be said that, a relatively low cost is possible now to prepare UHPC. The preparation of UHPC is becoming more economical and sustainable. 3.2
Microstructure
From material science point of view, the macro properties
Examples of composition and properties of NSC, HSC and UHPC [14] Component (kg/m3) Portland cement Coarse aggregate Sand Silica fume Reinforcement/Fibers Superplasticizer Water Other parameters Maximum aggregate size (mm) w/c ratio (by weight) w/b ratio (by weight)
NSC
HSC
UHPC
200
400 900 600 40 designed 5 100–150
600–1000 1000–1200 50–300 40–250 10–70 110–260
19.0–25.5
9.5–12.5
0.15–0.6
0.40–0.70
0.24–0.38
0.14–0.27
