Page 446 - New Trends in Eco efficient and Recycled Concrete

398 New Trends in Eco-efficient and Recycled Concrete

mainly recycled concrete aggregates (RCA) have been proposed to be an effective
way to solve the problem of CDW disposal, since the conventional landfill method
would take up lots of soil and would cause many secondary pollutions (Hansen,
1985). Previous studies have shown the feasibility of using RA in the of mortars
and concrete manufacture (Kou et al., 2011; Ledesma et al., 2014; Beltra ´n et al.,
2014; Agrela et al., 2017). The inferior properties of RAC and RA mortars manu-
factured with RA are mainly attributed to the mortar adhered to the RA, which give
rise to lower densities, greater water absorption and lower resistance (Tabsh and
Abdelfatah, 2009; Shi et al., 2010; Shi and Wang, 2009).
The use of AASs or geopolymers in the manufacture of RAC, including its sub-
stitution of cement, have been studied in order to mitigate its detrimental effect
with an appropriate mix design (Kou et al., 2007, 2008). The alkali-activation of
RCA with a proportioned alkali-activator can show the possibility of manufacturing
AASm and AASc from these materials as a basis. The mechanical behaviour of the
products manufactured with RA with different components (concrete, ceramic parti-
cles and asphalts, etc.), shows that the properties acquired by these materials are
suitable for use on an industrial scale, but it is necessary to optimise the mixtures
made and the type of activator (Allahverdi et al., 2011).
Among the cementitious components used in the manufacture AASm and AASc
may be included as cementitious materials with hydraulicity (slag, OPC) or pozzo-
lanic properties (Fig. 13.29). The alkaline activation is presented as a potential tech-
nology because both natural materials (such as clay or feldspars) and industrial by-
products (such as slag, FA and PS) can be main materials.
Precursors are defined as the main product of hydration in the binders. The main
precursors used are based on AAS and FA calcium-silicate-hydrates and complex

Figure 13.29 Alkali-activated system components (Garcia-Lodeiro et al., 2015).