Page 170 - New Trends in Eco efficient and Recycled Concrete

142 New Trends in Eco-efficient and Recycled Concrete

(3) calcination of SS with the addition of lime. There were minor differences

among the types of SSA obtained at 800 C, although SSA without any lime added
(as stabilising agent or as addition in the calcination) presented the best mechanical
results when used for 10 and 20 replacement percentages for cement mortars.
Mixtures of PC-SSA in the ratios of 20:80, 30:70 and 40:60 (by weight) were
used to prepare foamed lightweight materials (Wang and Chiou, 2004) using alumin-
ium powder (0.9% 1.3% referred to as total solid) or mixed scrap metal waste pow-
der as foaming agents. The results show that compressive strength of aluminium
powder specimens was lower than those that used the mixed scrap metal waste as a
foaming agent. This tendency was confirmed by the total pore volume data. The pres-
ence of SSA in the mixtures increased the proportion of pores smaller than 10 μm,
probably due to pozzolanic reaction products and the morphology of the ashes.
Garcı ´a-Alcocel et al. (2006) demonstrated that the pozzolanic reactivity of SSA
was moderated and studied the corrosion of embedded rebars in PC mortars con-
taining 0% 60% of SSA replacement. They found that metallic corrosion for mor-
tars containing 10% SSA had similar behaviour than plain cement mortar in 100%
RH and under seawater. The washing of SSA with distilled water was an interesting
procedure for enhancing mortar properties from the corrosion point of view.
Cyr et al. (2007) studied SSA replaced mortars by 25% and 50% by weight of
PC. Compressive and flexural strength development for these mortars are shown in
Fig. 5.10. It can be seen that the strength evolution for the short curing time was
much lower for SSA mortars, especially for the 50% replaced case. However, after
28 days, a significant contribution of SSA was highlighted. Calorimetric studies
showed that heat flow for plain cement mortar started after 3 h of mixing.
However, for 25% and 50% SSA samples, heat flow started after 4.5 and 6.5 h,
respectively. This delay was attributed to both a dilution effect and the presence of
several chemical elements (P, Zn) in the ash.
Blending different mineral admixtures [such as FA and blast furnace slag
(BFS)], Yen et al (2012) obtained interesting results by replacing 50% of PC.
Binary SSA 1 FA and SSA 1 BFS and ternary SSA 1 FA 1 BFS were studied. The
authors reported that the best mixtures were those that contained the binary system
25% SSA 1 75% BFS and the ternary system 25% SSA 1 50% FA 1 25% BFS,
reaching relative compressive strengths, with respect to the control mortar, of
93.7% and 92.9% at 56 days of curing. In the same way, Baeza et al. (2014a) tested
binary SSA blends with FA, MD and RHA. They found that after 90 days of curing,
84.7% of the reference mortar was achieved for the 10% SSA 1 10% FA mortar
and 91.3% for the 10% SSA 1 10%RHA one. However, MD did not contribute to
good strength development (75.8% for 10% SSA 1 10% MD with respect to the ref-
erence) and it was lower than that found for 20% SSA (78.5%). The ternary mixture
10% SSA 1 10% FA 1 10% RHa yielded the best result, with 109.4% respect to
the reference, which was much higher than that found for 30% SSA (59.3%).
SSA has been also tested as a sand replacement in the fabrication of dry consis-
tency concrete blocks (Baeza et al., 2014b). A similar strength to the control block
was obtained, and 10% of sand replacement by SSA yielded blocks with the
best performance in terms of absorption, density and capillary suction. The