Chapter 11 Recent Advances of cement-based materials

2 High-strength concrete 1 Definition 2 High-strength concrete 3 Self-Compacting Concrete Advanced Concrete 4 High-Performance Concrete 5 Shrinkage-Compensating Concrete 6 Fiber-Reinforced Concrete

7 Concrete Containing Polymers Advanced Concrete 8 Heavyweight concrete 9 Mass Concrete

1 Preview Ordinary concrete----made with natural aggregate, has a low strength-weight ratio compared to steel. Disadvantage----tall buildings, long-span bridges, and floating structures.

1 Advanced concrete Advanced the density can be reduced the strength can be raised combine the first two approaches above of three approaches

2 High strength concrete 2.1 Definition Strength of the matrix Strength of the interfacial transition zone Concrete strength

2 High strength concrete 2.1 Definition O.C H.S.C S.S.C Compressive strength 60 80 MPa Ordinary concrete: Compressive strength <60 MPa. High-strength concrete: Compressive strength>60 MPa. It is applied largely to the high- rise building, large span bridge and high-strength prefabrication component and so on. Super-strength concrete: Compressive strength>80 MPa.

2.2 Choice of HSC Raw material 2 High strength concrete 2.2 Choice of HSC Raw material Binding Material Characteristics of cement kinds and grades mineral composites and fineness Quantity of cement

2.2 Choice of HSC Raw material 2 High strength concrete 2.2 Choice of HSC Raw material Kinds and Grades Normally, these kinds of cement, can obtain higher final strength is applied in improving consistent strength. such as high-mark Portland cement ordinary Portland cement slag Portland cement pozzolan Portland cement

2.1 Choice of HSC Raw material 2 High strength concrete 2.1 Choice of HSC Raw material Kinds and Grades In the past, it was difficult to mix high-strength concrete. That is, the mark of cement should be higher than strength grade of concrete, or sometimes be slightly lower than strength grade of concrete. In our country, at present, it is much easier to mix high-strength concrete with the modification of material properties and craftworks especially the wide use of admixture.

2.1 Choice of HSC Raw material 2 High strength concrete 2.1 Choice of HSC Raw material Mineral Composites and Fineness Fineness of cement can influence strength of concrete. surface area is 3500-4000cm2/g. The finer levigating, the large surface area, the more sufficient hydration reaction, the higher strength

2.1 Choice of HSC Raw material 2 High strength concrete 2.1 Choice of HSC Raw material Quantity of Cement The quantity of binding material is so important to produce HSC that it directly influences the cohesion between hardened cement paste and border surface. Construction requirement also needs certain feasibility. In order to increase the proportion of binding material in mortar, the usage of cement is large usually in the range of 500-700kg／m3. But it is recommended not out of this range otherwise it is easy to cause slow heat radiation and large shrinkage in hydration.

2.1 Choice of HSC Raw material 2 High strength concrete 2.1 Choice of HSC Raw material Excellent Aggregate fine aggregate Sand modulus of fineness lower than 3.0 and reduce sand rate Concrete admixture should not be too dry or hard. In the composites of HSC, fine admixture percentage is smaller than that of the ordinary concrete. It is better to use quartz river sand as the chemical composite of sand.

2.1 Choice of HSC Raw material 2 High strength concrete 2.1 Choice of HSC Raw material Excellent Aggregate coarse aggregate Concrete strength is influenced by coarse aggregate by the following factors, cement paste, cohesion of mortar and aggregate, aggregate elasticity, stress concentration around the aggregate. For HSC coarse aggregate has good performance in compressive strength, surface, maximum grain-size.

2.1 Choice of HSC Raw material 2 High strength concrete 2.1 Choice of HSC Raw material Superplasticizer HSC can be obtained by high grade cement and superplasticizer. Polycarboxylate Superplasticizer Reducing water usage

2 High strength concrete 2.2 Application JinMao Tower，C60 Skyscraper E-Tower building,Brazil

3 Self-Compacting Concrete 3.1 Problem How to produce concrete mixtures possessing a high workability? Development of high-workability concrete mixtures that are known by self-compacting concrete

3 Self-Compacting Concrete 3.2 Definition The self-compacting concrete (SCC) may be defined as a flowing concrete that can be cast into place without the use of vibrators to form a product.

3 Self-Compacting Concrete 3.2 Development Although superplasticizing admixtures are expensive, the ability to place concrete rapidly and to consolidate it with little or no cost presents savings that may equal or even exceed the cost of the superplasticizer, while producing a better quality end product.

3.2 Materials and mixture proportions 3 Self-Compacting Concrete 3.2 Materials and mixture proportions

3 Self-Compacting Concrete 3.3 Properties --Superior rheological characteristics --Slump value in excess of 200 mm --Slump-flow value in excess of 600 mm --Be placed and compacted without the help of vibrators

3 Self-Compacting Concrete 3.4 Applications Europe and Japan---underwater concreting and for the construction of heavily reinforced structures North America --- precast concrete plants where there is a high degree of quality control China--- long-span bridge, high-rise buildings Sutong Bridge，2008

4 High-performance Concrete high workability high durability high ultimate strength High-performance concrete (HPC) for concrete mixtures possessing high workability, high durability and high ultimate strength.

4 High-performance Concrete 4.1 Definition ACI defined high-performance concrete as a concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing, and curing practice. 1990 The first international conference in USA

4 High-performance Concrete 4.2 Characteristics Examples of characteristics that may be considered critical for particular application are: ---Compaction without segregation --- Early age strength ---Long-term strength and mechanical properties --- Permeability --- Density ---Heat of hydration ---Toughness ---Volume stability ---Long life in severe environments

4.3 Structure and properties 4 High-performance Concrete 4.3 Structure and properties Fly ash Slag Silica

4 High-performance Concrete 4.4 Applications Long span bridges Highway CCTV Building Steel fiber reinforced self-compacting concrete

5 Shinkage-Compensating concrete 5.1 Definition According to ACI, shrinkage-compensating concrete is an expansive cement concrete which, when properly restrained by reinforcement of other means, will expand an amount equal to or slightly greater than the anticipated drying shrinkage. Because of the restraint, compressive stresses will be induced in the concrete during expansion. Subsequent drying shrinkage will reduce these stresses.

5 Shinkage-Compensating concrete 5.1 Definition Concrete containing a hydraulic cement, water, aggregate, and discontinuous discrete fibers is called fiber-reinforced concrete. Containing pozzolans and other admixtures Fibers of various shapes and sizes produced from steel, plastic, glass, and natural materials are being used, steel fiber is the most commonly used of all the fibers.

6 Fiber-reinforced concrete 6.1 Type of fiber The type of fiber and its volume fraction has a marked effect on the properties of fiber reinforced concrete. It is convenient to classify the fiber reinforced composites as a function of their fiber volume fraction:

6 Fiber-reinforced concrete 6.2 Type of fiber Low volume fraction (<1 percent). The fibers are used to reduce shrinkage cracking. These fibers are used in slabs and pavements that have a large exposed surface leading to high shrinkage cracking. Moderate volume fraction (between 1 and 2 percent). The presence of fibers at this volume fraction increases the modulus of rupture, fracture toughness, and impact resistance.

6 Fiber-reinforced concrete 6.2 Type of fiber High volume fraction (greater than 2 percent). The fibers used at this level lead to strain-hardening of the composites.

6 Fiber-reinforced concrete 6.2 Type of fiber High volume fraction (greater than 2 percent). The fibers used at this level lead to strain-hardening of the composites.

6.2 Type of fiber

6 Fiber-reinforced concrete 6.3 Properties Workability. For most applications, typical mortar or concrete mixtures containing fibers possess very low consistencies; however, the placeability and compactibility of the concrete is much better than reflected by the low consistency Strength. It can be seen that increasing the length of fibers up to a point increases strength as well as toughness.

6 Fiber-reinforced concrete 6.3 Properties Toughness and impact resistance. The greatest advantage in fiber reinforcement of concrete is the improvement in flexural toughness consistency. Related to flexural toughness are the impact and fatigue resistance of concrete, which are also increased considerably.

6 Fiber-reinforced concrete 6.3 Properties Elastic modulus. Inclusion of steel fibers in concrete has little effect on the modulus of elasticity. Durability. Fiber-reinforced concrete is generally made with a high cement content and a low water-cement ratio. When well compacted and cured, concretes containing steel fibers seem to possess excellent durability as long as fibers remain protected by the cement paste.

6 Fiber-reinforced concrete 6.3 Properties Figure 10 Factors affecting properties of fiber-reinforced concrete: (a) influence of increasing fiber volume; (b) influence of increasing the aspect ratio.

6.4 Development of ultra-high-performance fiber-reinforced composites 6 Fiber-reinforced concrete 6.4 Development of ultra-high-performance fiber-reinforced composites Compact reinforced composites. Researchers in Denmark created compact reinforced composites using metal fibers, 6 mm long and 0.15 mm in diameter, and volume fractions in the range of 5 to 10 percent. These short fibers increase the tensile strength and toughness of the material.

6.4 Development of ultra-high-performance fiber-reinforced composites 6 Fiber-reinforced concrete 6.4 Development of ultra-high-performance fiber-reinforced composites Reactive powder concrete (RPC). The material can obtain a compressive strength of 200 MPa when cured in hot water at 90°C for three days and a compressive strength of 800 MPa when cured at 400°C.

6.4 Development of ultra-high-performance fiber-reinforced composites 6 Fiber-reinforced concrete 6.4 Development of ultra-high-performance fiber-reinforced composites Reactive powder concrete (RPC). The material can obtain a compressive strength of 200 MPa when cured in hot water at 90°C for three days and a compressive strength of 800 MPa when cured at 400°C.

6.4 Development of ultra-high-performance fiber-reinforced composites 6 Fiber-reinforced concrete 6.4 Development of ultra-high-performance fiber-reinforced composites Reducing the deadweight of structure Improving the durability of structure Good toughness High temperature resistance Fire resistance

6.4 Development of ultra-high-performance fiber-reinforced composites 6 Fiber-reinforced concrete 6.4 Development of ultra-high-performance fiber-reinforced composites Slurry-infiltrated-fibered concrete (SIFCON). The processing of this composite consists of placing the fibers in a formwork and then infiltrating a high w/c ratio mortar slurry to coat the fibers. Fibers with high surface area are used. Compressive and tensile strengths up to 120 and 40 MPa.

6.4 Development of ultra-high-performance fiber-reinforced composites 6 Fiber-reinforced concrete 6.4 Development of ultra-high-performance fiber-reinforced composites Engineered cementitious composite (ECC). The material has a very high strain capacity and toughness and controlled crack propagation . Ductility，500 times Light，40%

7 Polymer concrete 7.1 Definition Polymer concrete (PC) is a mixture of aggregates with a polymer as the sole binder. To minimize the amount of the expensive binder, it is very important to achieve the maximum possible dry-packed density of the aggregate. It was important to use dry aggregate because the presence of moisture caused a serious deterioration in the properties of the polymer concrete.

7 Polymer concrete 7.1 Definition Polymer concrete (PC) is a mixture of aggregates with a polymer as the sole binder. To minimize the amount of the expensive binder, it is very important to achieve the maximum possible dry-packed density of the aggregate. It was important to use dry aggregate because the presence of moisture caused a serious deterioration in the properties of the polymer concrete. Polymer conctent : in the range of 5-20% Application: Repairing of pavement and others

7.2 Mechanism and properties 7 Polymer concrete 7.2 Mechanism and properties Mechanism The density of polymer concrete can be increased because the pores and microcracks are filled by the polymers. Properties High strength Permeability resistance Frost resistance Corrosion resistance

8 Heavyweight concrete 8.1 Definition Concrete is commonly used for biological shielding in nuclear power plants, medical units, and atomic research and testing facilities. Heavyweight concretes are produced generally by using natural heavyweight aggregates. The concrete unit weights are in the range 3370 to 3840 kg/m3, which is about 50 percent higher than the unit weight of concrete containing normal-weight aggregates.

8 Heavyweight concrete 8.2 Properties Heavyweight concrete can be pumped or placed by chutes over short distances only, because of the tendency of coarse aggregate to segregate. Unit weights of concrete containing barite, magnetite aggregate are in the range of 3450 to 3760 kg/m3; when hydrous and boron ores (which are not of high density) are used as partial replacement for heavyweight aggregate, the unit weight of concrete may come down to about 3200 to 3450 kg/m3. 2000 to 2800 kg/m3

8 Heavyweight concrete 8.3 Applications Nuclear power plant

9 Mass concrete 9.1 Definition ACI has defined mass concrete as concrete in a massive structure, for example, a beam, columns, pier, lock, or dam where its volume is of such magnitude as to require special means of coping with the generation of heat and subsequent volume change.

9 Mass concrete 9.1 Definition Thermal stress and temperature control is crucial in mass concrete structure. Temperature rise in concrete due to heat of hydration, and subsequent shrinkage and cracking that occurred on cooling If they are several meters thick and are made of high-strength concrete mixtures (high cement content), the problem of thermal cracking can be as serious as in dams

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