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Application of alkali-activated industrial waste 387

Figure 13.21 Variation of drying shrinkage with curing time of fly ash activated mortars
with 0% 10% of dry paper sludge (Yan and Sagoe-Crentsil, 2012).

ignition (LOI), 51.8% cellulosic matter). The addition of 10% of the sludge reduced
the flow of mortars and diminished the compressive strength by 50%. The drying
shrinkage values of alkali activated mortars incorporating 2.5% and 10% PS were
34% and 64% less if compared to the reference mortar, demonstrating the
shrinkage-reducing role of this dry PS additive (Fig. 13.21).
Silica rich waste (89.2% SiO 2 ) produced in the flue gas scrubbing treatment of
chlorosilane production was studied by Gluth et al. (2013). A mixture (4:3 ratio)
with sodium aluminate was carried out by mixing with water (0.6 water to solid
ratio). After curing 7 days at 70 C, the samples yielded 7 MPa in compressive

strength.

13.2.1.6 Agro-industrial wastes
There are many agro-industrial ashes that have been tested as pozzolanic materials
in Portland cement blends because of their high content in amorphous silica.
Table 13.4 summarises the chemical composition of some selected agro-industrial
ashes that have been reported in geopolymer studies. In most cases, the Al 2 O 3 con-
tent was less than 5%, and, consequently, it is not possible the use of ash alone to
produce geopolymers due to its unsuitable SiO 2 /Al 2 O 3 ratio. In some cases, the rel-
ative high Al 2 O 3 and Fe 2 O 3 content was attributed to the soil contamination.
RHA was blended with different mineral additions to form geopolymers. RHA/
FA blends were analysed in several studies (Detphan and Chindaprasirt, 2009;
Huynh et al., 2017; Hwang and Huynh, 2015). Huynh et al. (2017) prepared FA/
RHA 2:1 ratio blends and observed that 20 35 MPa in compression was achieved