Page 444 - New Trends in Eco efficient and Recycled Concrete

396 New Trends in Eco-efficient and Recycled Concrete

resulting ash had 61% CaO, 12.0% K 2 O and 8.70% MgO. Several HCWA/FA
blends were prepared and mixed with water. The mortars set at room temperature

(28 6 5 C) and were stored under HL saturated solution. Specimens were tested in
compression after 7, 28 and 90 days of curing (Ban et al., 2017). Fig. 13.27 shows
the strength values. The hardened binder phase primarily consisted primarily of
potassium polysialate (K A S H), tobermorite and gehlenite hydrate geopoly-
meric framework. In a previous study, these authors (Cheah et al., 2015) found that
mortars with 0.42 water/solid ratio and HCWA contents of 50% and 60% showed
good mechanical and durability performances.
Peys et al. (2016) tested some biomass ashes as an alkaline activator in the MK-
based geopolymer synthesis. Maize stalk and maize cob ashes reached pH 5 13 14
after mixing with water. The K 2 O content was 30% 32% and SiO 2 was 18%
21%. Geopolymers were synthetised by mixing ash, MK and water, and the pastes
were cured at 80 C. Maize cob ash yielded the best mechanical behaviour (30 MPa)

for pastes with ash/MK ratios of 0.9 and 1.2 cured for 2 days in an 80 C water
bath. Font et al. (2017a,b) activated blast furnace slag with olive-stone biomass ash
(OBA). The ash had 27.77% CaO, 32.16% K 2 O and 5.13% MgO and it was previ-
ously ground. BFS mortars were activated with water (M1), 4 M KOH solution
(M2) and 0.47 ratio OBA/water suspension (M3). After curing for 3 and 7 days at

65 C, OBA containing BFS activated mortars showed the best behaviour
(Fig. 13.28). It was suggested a synergic process in terms of the filler and chemical
effects.

Figure 13.27 Compressive strength values for HCWA/FA mortars cured at room
temperature prepared with 0.35 and 0.30 water/solid ratios (Ban et al., 2017). HCWA, High
calcium wood ash; FA, Fly ash.