Mechanical and durability performance of metakaolin and fly ash-based geopolymers compared to cement systems

Abstract

The environmental impact of Ordinary Portland Cement production, particularly its significant contribution to global CO2 emissions, has prompted the search for sustainable alternatives. This study investigates the durability and mechanical performance of metakaolin and fly ash-based geopolymer formulations compared to cement-based systems (CEM I and CEM III) under aggressive environmental conditions, without the use of heat curing. Among the six binder types tested, metakaolin-based MK II achieved a compressive strength of 33 MPa at 90 days—comparable to CEM III (35.2 MPa)—and the lowest water absorption (3.4 %). MK II also exhibited the highest durability, with superior resistance to carbonation, sulfate, and acid attacks, as well as minimal ultrasonic pulse velocity loss in the boiling test. Cement-based samples, particularly CEM I, displayed the best freeze-thaw resistance and lowest porosity increase after 150 cycles. Fire resistance testing classified MK I, MK II, and CEM III as A1-rated non-combustible materials. These results highlight the potential of metakaolin geopolymers—especially MK II—as sustainable, durable alternatives to cement, capable of performing in aggressive environments without additional energy input.