Properties of Fresh and Hardened Concrete

Table 2.5 Mixture proportions and properties of fresh and hardened concrete (water reduced)...

Properties of Fresh and Hardened Concrete 201 Table 12.3 Classes of compressive strength of normal-weight concrete [3]... 

The water reducing admixtures are the materials that have the primary function of producing concrete of a specified workability at a lower watencement ratio than that of the control concrete without admixture. The effect of water reducing admixtures on various properties of fresh and hardened concrete is illustrated in Figure 5.9 [23, 26]. 

Admixtures are substances that are added during the mixing process in small quantities related to the mass of cement, in order to improve the properties of fresh or hardened concrete [7,8]. The most utilised admixtures are water reducers and superplasticizers that may be added to improve the workability of concrete or reduce the amount of mix water accelerators that are used to increase the rate of development of early strength of concrete set-retarders that reduce the setting time of concrete air-entraining agents that increase the freeze-thaw resistance of concrete (Section 3.1). Recently, corrosion inhibitors have been developed in order to increase the corrosion protection of embedded steel these will be treated in Chapter 13. 

Asphalt concrete is properly proportioned to resist the potentially damaging effects in the road. Asphalt concrete paving mixtures should be evaluated for the following properties stability, flow, air voids, stripping resistance, resilient modulus, compacted density, and unit weight. Table 4.18 provides a list of standard laboratory tests that are presently used to evaluate the mix design or expected performance of fresh and hardened asphalt concrete. 

A comprehensive overview of the properties of superabsorbent polymers, specific water absorption and desorption behavior of superabsorbent pol5uners in fresh and hardening concrete, the effects of the superabsorbent pol5uners addition on the rheological properties of fresh concrete, the changes of cement paste microstructure and mechanical properties of concrete have been reviewed (42). 

Uomoto and Kobayashi [8] described an electromagnetic method which can be used to determine the steel fibre contents of both fresh and hardened concretes. The system measures the current changes induced by the ferromagnetic properties of the concrete, which are a function of the steel fibre content. For evaluation of the fibre content in fresh concrete, plastic moulds must be used (as they do not induce an electrical current by themselves). It should be noted that methods of this kind are not applicable to non-ferromagnetic fibres such as polypropylene, for which wash-out methods must be developed. 

For the last decades concrete producers have made wide use of waste or by-product materials in concrete [1,2]. Proper replacement of these materials in concrete would have two major significant improving fresh and hardened properties of concrete and minimizing the environmental pollutions due to solid waste disposal. 

Latex-modified mortar and concrete are made by using a composite binder of inorganic cements and organic polymer latexes, and have a network structure which consists of cement gels and microfilms of polymers. Consequently, the properties of the latex-modified mortar and concrete are markedly improved over conventional cement mortar and concrete. The properties of the fresh and hardened mortar and concrete are affected by a multiplicity of factors such as polymer type, polymer-cement ratio, water-cement ratio, air content, and curing conditions. 

A review of research on the performance of concrete containing GRT particles was recently published (Pacheco-Torgal et al., 2012). In particular, this review discussed the effect of GRT treatment, the size of GRT particles, and the replacement volume on the fresh and hardened properties of concrete. A workability of fresh concrete defining its flowability and the compressive and tensile strength, toughness, elastic modulus, thermal and sound properties, and durability of hardened concretes containing the tire rubber waste was also discussed. 

Some chemical agents, introduced in small amounts, can facilitate the production process, or modify the properties of the resulting cement or those of the fresh concrete mix and hardened concrete. They include... 

J. Nilsson, and P. Scugenius, Effect of microtibriUcir cellulose on concrete equivalent mortar fresh and hardened properties, KTH, ABE, Department of Civil and Architectural Engineering. (2011). 

In the mix composition of advanced cement-based materials a few admixtures for improving their special properties in fresh and in hardened states are normally included (cf. Section 4.3). In particular, different water reducers and plasticizers are used in a large majority of concrete production. This trend will intensify in the future, based on the results of investigations. 

Silica fume is a by-product from the silicon metal or ferro-silieon industry. Its particle size ranges from 0.1 pm to 0.2 pm, the surface area being 20-23 m /g. It is highly pozzolanic and improves the properties of concrete in fresh and hardened states. 

The properties of an aggregate influence both the characteristics of the fresh mix and the strength and durability of the hardened concrete. 

Concrete in the fresh state should have good workability in order to be properly placed and compacted in the mould so that it can reach the expected properties after hardening. The most relevant properties of hardened concrete are strength, deformation due to loading or thermal and moisture variations, resistance to cracking, and durability. 

Polymers. The purpose of adding polymers to the concrete matrix is to improve the characteristics of the fresh concrete (such as workability) and also to enhance the hardened properties such as flexural strength, modulus of elasticity and adhesive performance [8]. The incorporation of polymers into concrete may be in the form of polymer modified concrete (PMC), polymer impregnated concrete (PIC) or as polymer concrete (PC) [9], For this project, the objective was to develop an ultra-lightweight concrete material using Portland cement as the main binder modified with a suitable polymer - thus a PMC application. The polymer modifiers selected for the development of the ultra-lightweight thin filmed material were a commercially available SBR latex as well as a readily available acrylic polymer. 

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