Effect of wastes as supplementary cementitious materials on the transport properties of concrete

The valorization of waste material for building applications has a long and successful history. Nowadays, byproducts such as fly ash, ground-granulated blast furnace slag (GGBFS), and silica fume are usual constituents of cement and concrete. These supplementary cementitious materials (SCMs) are recognized for enhancing certain properties of concrete, while also reducing its environmental impact. The huge amount of cement consumed globally demands additional sources of SCMs. A number of waste materials are prospective candidates, and reports on almost any type of waste being used in cementitious materials can be found in the present literature. The comprehensive study of their capabilities should comprise their ecological, economic, and engineering benefits. This chapter focuses on the effect of alternative SCMs from wastes on the transport properties of concrete. Transport properties are important for durability and performance in the service life of concrete structures. The most usually assessed transport properties are water transport (permeability, sorptivity, and absorption), gas permeability (oxygen and air), carbonation, ion transport (chloride penetration and lixiviation), and electrical resistivity. Although they are connected, there are specific features to observe for each case. The effect of SCMs on transport properties mainly depends on the chemical and physical modifications that they cause in the microstructure. Some properties are more affected by chemical changes, whereas others are more affected by physical changes. The analysis of transport properties in cementitious materials with waste used as SCMs allows developing the most convenient cementitious systems containing them. Alternative sources of SCMs are numerous; therefore a comprehensive analysis of all of them is rather difficult. This chapter offers a review of a limited number of types of waste that have been tested as SCMs in cement, mortar, and concrete. Byproducts that are already extensively used in the market (e.g., fly ash,GGBFS, limestone powder, and silica fume) are not included in this review. The selected materials are not necessarily the ones that demonstrate the most convenient technical or commercial features but the ones with which the authors have more experience. Some of the comments in this chapter are certainly applicable to other types of SCMs, so the content may still be valuable for readers interested in other types of SCMs not included in this section.