The usage of a natural silty soil as an aggregate to manufacture
sustainable geopolymer masonry units has been pioneered by
Sukmak et al. [34–36]. It was reported that the 7-day strength of
the soil-FA geopolymer is greater than 10 MPa, deeming it suitable
as a bearing masonry unit. The durability against sulfate attack of
soil-FA geopolymer is superior to that of clay-cement; i.e., there
is no major change in the microstructure and pH of soil-FA
geopolymer when exposed to sulfate solutions.
Recently, Suksiripattanapong et al. [22] investigated the
strength development in WTS–FA geopolymer as a bearing
masonry unit. The NaOH and Na2SiO3 were used as a liquid alkaline
activator while high calcium fly ash was used as a precursor. The
optimum ingredient providing maximum unit weight and strength
is NaOH/Na2SiO3 ratio of 80:20 and L/FA ratio of 1.3, irrespective of
heat condition and curing time. The optimum heat temperature
and duration for the optimum ingredient are 75 C and 72 h,respectively. The durability against wet-dry of WTS–FA geopolymer
is superior to that of WTS-cement as the alum in WTS retards
the cement hydration