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 CO 2 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.