Page 171 - New Trends in Eco efficient and Recycled Concrete

Sewage sludge ash 143

70 Reference 66.6
62.0 61.2
25% SSA 54.8 45.0 57.0 50.7 55.7
Compressive strength (MPa) 40 28.7 19.1 41.3 31.1 19.4 32.7
60
50% SSA
50

30
20
10
0 12.5
1 2 7 28 84
Hydration time (days)
9 Reference
7.8 7.5
25% SSA
8 7.2 7.0
50% SSA 6.4 6.2 5.3 6.6 7.1 6.7
Flexural strength (MPa) 5 4 3 4.3 4.9 4.0
7
5.2
6

1 2 1.9
0
1 2 7 28 84
Hydration time (days)
Figure 5.10 Flexural and compressive strength development for control mortar (reference)
and mortars containing SSA (25% and 50% by weight) for 1 84 day time period (Cyr et al.,
2007). SSA, Sewage sludge ash.

enrichment of the mix with the fine SSA particles likely enhanced the development
of the block performance. Jamshidi et al. (2013) found that replacement of sand by
SSA in 5% 10% by weight of cement yielded similar compressive strength than
reference concrete after 90 days of curing. In contrast, Bhatty and Reid (1989)
found that replacement of sand by SSA reduced the strength significantly.
Reactivity of SSA was compared to the FA case (Piasta and Lukawska, 2016)
and it was concluded that SSA presented lower pozzolanic behaviour in terms of
strength gain. Thus, pozzolanic activity of SSA can be considered as moderated.
Pavlı ´k et al. (2016) also found a low reactivity of SSA in the first 28 days of curing,
attributing this to a simple filler effect that contributed to cement paste strength.
The authors analysed the porosity and mechanical behaviour of cement pastes con-
taining SSA in the 0% 60% replacement range. The total porosity increased with
the replacement percentage (Fig. 5.11A) and they found a relationship between
porosity, compressive and bending strength (Fig. 5.11B).