Alkali activated construction materials: Assessing the alternative use for oil shale processing solid wastes

The potential of oil shale ash wastes as a source material for geopolymeric or alkali activated construction materials was assessed using structural, XRD, SEM, SEM-EDX, ATR-FTIR and 29Si MAS-NMR methods. Fresh, unhydrated furnace bottom and cyclone separator ash along ash plateau sediment were used in combination with 5 M NaOH and Na2SiO3 solutions with SiO2/Na2O ratios of 2.72 and 1.5 as alkaline activators, under ambient curing conditions. Our analytical results show that only activator solutions containing soluble silicate will induce the formation of amorphous C-(A)-S-H gel, giving the samples 8 times higher compressive strength (8.5 MPa) than samples exhibiting cementitious properties upon hydration (1.25 MPa).