Page 428 - New Trends in Eco efficient and Recycled Concrete

Application of alkali-activated industrial waste 381

samples. The 10% replacement did not reduce the compressive strength after 7 days
curing at room temperature. Precursors obtained by blending SSA and BFS also
were tested (Tashima et al., 2017). The best compressive strength results were
obtained in 20% SSA blended mortars (6 M NaOH activated). Honeycomb-like
C A S H gel was the binding phase. Chakraborty et al. (2017) reported that the
use of quick lime (QL, 20% replacing SSA) significantly enhanced the compressive
strength from 5 to 20 MPa. Ternary blend consisting in SSA/QL/BFS 70:20:10
raised the strength to 30 MPa.
Non-calcined, dried, wastewater treatment sludge was used for geopolymer for-
mulation by blending it with coal FA (Suksiripattanapong et al., 2015). Different
Na 2 SiO 3 /NaOH ratios were tested (from 100:0 to 50:50) for activating the sludge/
FA 70:30. The samples were compacted under the modified Proctor energy and
were pre-cured in the range 65 85 C for 24 120 h. After this, the pastes remained

at room temperature until the mechanical test. Sludge/FA made up at optimum
ingredients (Na 2 SiO 3 /NaOH ratio of 80:20 and liquid/FA ratio of 1.3) and heated at

75 C yielded between 12 and 20 MPa in compressive strength.
Pre-washed MSWI FA was used in the manufacturing of geopolymer materials
showing low temperature setting (Ferone et al., 2013). The stabilisation of MSWI
was carried out in systems containing coal FA (MSWI/FA ratio of 1:3) by means of
the activation with NaOH solution. As received and pre-washed MSWI FAs were
compared, physico-mechanical tests showed that MSWI washing became very
advantageous from the safer ash disposal point of view. Wongsa et al. (2017) stud-
ied the compatibility of MSWI-ba and high-calcium coal FAs. The microstructural
parameters (porosity, pore size distribution, and Scanning Electron Microscope
(SEM) micrographs) indicated that the use of MSWI-ba increases geopolymer
matrix performance. SEM micrographs (Fig. 13.16) showed that the 20% and 40%
MSWI containing pastes were denser than 0% and 100% samples.
MSWI/MK 40:60 blend (Jin et al., 2016) was geopolymerised by using NaOH/
Na 2 SiO 3 solution, maintaining a constant molar ratio of 0.3 for Na 2 O/SiO 2 and 4.7
for SiO 2 /Al 2 O 3 . Geopolymer paste yielded 40 MPa and, under acid attack (simu-
lated acid rain consisted in a mixture of H 2 SO 4 and HNO 3 ), the pastes lightly
decreased in strength: less than 20% at pH 5 3 and less than 10% at pH 5 5.

13.2.1.4 Construction and demolition wastes

Construction and demolition waste (CDW) consist of a large fraction of inorganic
materials, old concrete, rejected mortar and concrete, ceramics and gypsum, among
others, being the main components. In many cases, the main fraction in composed
of Portland cement-based materials from which recycled aggregates (RA) can be
retrieved. Hydrated cement paste, part of which could be in carbonated state and
fine aggregate are usually difficult to recover. Paya ´ et al. (2012) studied the possi-
bility of reuse the hydrated-carbonated Portland cement paste for geopolymer syn-
thesis. The carbonation of C S H and C A S H gel yielded CaCO 3 and a
mixture of silica/alumina gel. This gel was activated by means of NaOH/waterglass

solution, and mortars cured for 3 days at 65 C yielded 10 MPa. Dry and wet