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Sewage sludge ash 145

5.7 Alternative binders containing sewage sludge ashes

There are few articles in which the use of SSA as a precursor in geopolymer mor-
tars is described. In the first investigation (Yamaguchi and Ikeda, 2010), the waste
used was in the slag form, not in the ash form. SSS (SS slag) with CFA were

employed to fabricate geopolymeric materials cured at 80 C(Yamaguchi and
Ikeda, 2010). They concluded that the optimum percentage to obtain materials with
the best mechanical strength is 75% of CFA and 25% SSS. Additionally, they dem-
onstrated that 100-SSA geopolymer systems developed strength slowly, and solidi-
fication was very sluggish.
Istuque et al. (2016) studied the behaviour of incorporating SSA in MK-based
geopolymeric mortars. One of the principal problems of geopolymeric materials
based in MK is that at high curing temperature reduces the compressive strength
with time. The formation of zeolites can be the source of the strength reduction.
The authors proposed replacement of part of MK by SSA to improve this reduction.
The percentages of replacement were 10% and 20% by mass. The curing conditions

employed were 25 and 65 C, and the compressive strength was measured after 1, 3
and 7 days of curing. As seen in Fig. 5.12, the mortars cured at 65 C presented a

reduction in compressive strength with curing time, while at room temperature the

45 (A) Curing temperature: 65°C (B) Curing temperature: 25°C
37.0 ± 1.8 MKB-0 MKB-0
40 MKB-10 MKB-10
MKB-20 MKB-20
35 29.8 ± 1.5 26.4 ± 2.3 25.5 ± 2.1 28.8 ± 2.4
27.9 ± 2.5
26.4 ± 2.8
Compressive strength (MPa) 25 24.4 ± 0.5 16.5 ± 0.5 20.3 ± 2.7 15.0 ± 1.0 17.3 ± 0.9 21.1 ± 1.8 21.9 ± 1.3
30
19.0 ± 1.6
17.2 ± 2.0
16.6 ± 2.2
15.7 ± 1.3
20
15

10

5

0
1 day 3 day 7 day 1 day 3 day 7 day
Curing time

Figure 5.12 Compressive strength of metakaolin-based geopolymer mortars with different
replacement by SSA (0%, 10% and 20%) cured at: (A) 65 C (thermal bath, B series), and

(B) 25 C (room temperature, R series) (Istuque et al., 2016). SSA, Sewage sludge ash.