Page 490 - New Trends in Eco efficient and Recycled Concrete

440 New Trends in Eco-efficient and Recycled Concrete

Figure 14.13 Low magnification SE images of natural aggregates: (A) siliceous sand
(d 50 5 500 μm); (B) siliceous sand (d 50 5 1000 μm). Recycled aggregates obtained from a
standard concrete containing NA described in Fig. 14.12A, and crushed under laboratory
conditions (Guedes et al., 2013); (C) low magnification image; and (D) SE image showing
the compositional and structural complexity of RA, including NA, CH, FA and mortar and
the primary ITZ (arrow). SE, Secondary electron; RA, Recycled aggregate; ITZ, Interfacial
transition zone; NA, natural aggregates; FA, Fly ash.

14.4 Microstructural and morphological features of CDW
recycled aggregates

The microstructure of RAs is substantially different from that of NAs
(Fig. 14.12A C) because of the diversity inherent to the material primary composi-
tion, and strongly depend on processing and treatment. RA beneficiated from con-
struction and demolition waste (CDW) are usually classified as recycled concrete
aggregates (RCA), recycled masonry aggregates (RMA) or mixed RAs (MRAs)
(Silva et al., 2014). RCA contain above 90 wt% of cement-based fragments adhered
to NAs (Etxeberria et al., 2006; Silva et al., 2014); RMA contain above 90 wt% of
masonry materials including aerated and lightweight concrete blocks, ceramic
bricks, slag bricks and sand-lime bricks (Silva et al., 2014); MRA is a mixture of
RCA and RMA with less than 90 wt% of cement-based fragments and NA that may
contain other common CDW contaminants including wood, plastics, paints, asphalt,