Page 168 - New Trends in Eco efficient and Recycled Concrete

140 New Trends in Eco-efficient and Recycled Concrete

mixtures and compared to gypsum-cement mixtures with the same sulphate content,
and significant differences were found in their behaviour. For example, gypsum-
cement mixtures showed expansion higher than 1 mm/m after 180 days, while the
SSA-cement mixture had much lower expansion (0.190 mm/m).
Garce ´s et al. (2008) evaluated the suitability of SSA for blending with different
commercially available PCs. Durability aspects were tested (porosity and shrinkage
expansion) on mortars containing SSA. The results showed that total porosity
increased in all mortars containing SSA. In general, total porosity increased with
the PC replacement by SSA (Fig. 5.8). This fact suggests that water demand is a
crucial factor when the percentage of replacement is high, and consequently the
compaction level is low. No significant differences were observed between CEM
IIB-M(V-LL) 42.5R (a commercial cement with FA and ground limestone) and
CEM I 52.5R. This similar behaviour confirmed the advantage of using PC with
mineral additions plus SSA instead of PC without mineral additions, because
blended cements are cheaper and more environmentally friendly.
Paya ´ et al. (2002) studied the influence of binary binder admixture [SSA-coal
FA (CFA)] on the development of mortar strength. The results showed that the
presence of FA, in association with SSA and PC, became important for long curing
times (90 days), where the compressive and flexural strengths of the mortars were
similar, or higher, that the control one.
The influence of SSA fineness on mortar strength was studied by Pan et al.
(2003). Mortars replaced 20% by weight of PC by SSA were prepared. SSA was
2
ground in order to increase the fineness. SSA ground for 10 min showed 496 m /kg
2
Blaine fineness, and for 360 min it increased to 872 m /kg. The corresponding 20%
SSA-replaced mortars for each fineness yielded, at 28 days, 18.4 and 29.5 MPa,
respectively. These results show that the SSA pozzolanic activity and compressive

Figure 5.8 Total porosity of SSA containing mortars (0% 30% replacement of different
commercial cements) (Garce ´s et al., 2008). SSA, Sewage sludge ash