Investigation of un-calcined coal gangue together with ground granulated blast furnace slag and fly ash to ambient-curing production high-strength geopolymer

Aim of this work is to exploit an ambient-curing method to produce high-strength geopolymers by applying un-calcined coal gangue (G). An optimized alkaline activator solution with a mixture proportion of 1.2 M, 8% AE, and 0.32 liquid-solid ratio was adopted to stimulate the mixture of G, ground granulated blast furnace slag (S), and fly ash (A). The geopolymer totally composed of S displayed the highest strength, which was more than 70 MPa at 28 d. Compressive strengths dramatically decreased from 55 MPa to 20 MPa when the content of G changed from 25% to 55% in S-G binary geopolymers. The strength of S-A-G ternary geopolymers did not significantly influence by the content of G until 17%, and the strengths decreased with the increasing G content as it exceeded 22%. Appropriate contents of G resulted in aluminosilicate gel formation in the ternary S-A-G geopolymers, and compressive strengths of the ambient-curing ternary geopolymers can reach ∼65 MPa at 28 d.