Chapter 15: Properties of hardened concrete

This chapter deals with properties of hardened concrete, mainly dependent on composition and materials used, but also on production processes. A historical note is then presented from its simplest forms over 7000 years, its intense development in the nineteenth century with the discovery of Portland cement and the use of reinforced concrete, up to today, with concrete as the second most used material worldwide. Strength is then presented including test description. Failure mechanisms are then described with focus on cracking in compression, creep and shrinkage. The following sections deal with pore structure and transport mechanisms within the material – that is, permeability, diffusion and capillary absorption – making clear the importance of water/cement ratio and curing on concrete quality. Concluding the chapter, the influence of constituent materials – that is, cement, aggregate and admixtures – on hardened concrete properties is addressed. In terms of cement, the influence of alterations in compound composition of clinker is addressed, first referring to sulfate-resisting cement, low-heat cement, rapid-hardening cement and white cement. Second, the influence on concrete properties of additions such as slag and pozzolans – that is, metakaolin, rice husk ash, fly ash and silica fume – is addressed. Finally, as many of these materials are by-products or even waste materials, it is emphasised that their use as cement replacement materials reduces carbon dioxide emissions and enhances durability, therefore leading to greater economy and advantages in terms of environment and sustainable construction.