Page 174 - New Trends in Eco efficient and Recycled Concrete

146 New Trends in Eco-efficient and Recycled Concrete

strength increased. The addition of SSA to the mortars showed advantages in both

curing conditions. At 65 C, the compressive strength loss of mortars with SSA was
slightly less than in mortars with only MK. At room temperature, the mortar with
10% SSA replacement and the control with 100% MK presented a similar compres-
sive strength after 7 days.
Chakraborty et al. (2017) studied the improvement of adding quick lime (QL)
and blast furnace slag (BFS) to systems with SSA. They compared the performance
of mortars of SSA mixed with only water and mortars mixed with NaOH. They
studied different concentrations of NaOH and concluded that the best was 10 M.
With this concentration of NaOH, they studied the influence of substituting SSA by
QL and BFS. The maximum compressive strength was achieved with the mortar
that contained 70% SSA, 20% QL and 10% BFS. The addition of QL and BFS
promoted the formation of more hydrated products, which developed a more com-
pact matrix.
Finally, Tashima et al. (2017) published an investigation using SSA and ground
granulated blast furnace slag (GGBS). They activated the mixtures with only
sodium hydroxide, which were cured at room temperature. The mortar with 20% of
SSA and 6 mol/kg of NaOH achieved 31 MPa of compressive strength after 90
days of curing. This result is very important because it demonstrated the existence
of good mortars without using water by curing at room temperature. The main prod-
uct formed was a cementitious gel type, C-A-S-H.
Other alternative binders are the mixture of soil with cement and Chen and Lin
(2009) studied the stabilisation of a soft soil (with clay and silt) with a mixture 4:1
of SSA:cement. They substituted 16% of soil with the mixture of SSA/cement,
because the addition of this mixture promoted better soil performance. The charac-
teristics of the resulting soil were better than those demanded by legislation.
Along the same lines as previous article, Lin et al. (2016), studied the same
SSA/cement system and soil, but with the incorporation of nanosilica. The hydra-
tion products also increased with the addition of nanosilica, and therefore the
unconfined compressive strength (UCS) was 30 47 kPa higher than the soil with-
out this component.
Gu ¨llu ¨ and Fedakar (2017) proposed the stabilisation of soils with SSA and poly-
propylene fibre (PF). They employed ANOVA analysis to obtain the best propor-
tion of materials. The addition of 19.5% of SSA, 0.57% of PF and 12 curing days
resulted in a mixture with around 1900 kPa of UCS.

5.8 Other applications of sewage sludge ashes in
construction materials

The direct use of SSA in the preparation of cement includes blending it with
Portland clinker replacing part of the commercial cement by SSA, and using alter-
native binding materials. Some reports have also been done regarding the indirect