Enhancing the Durability Properties of Sustainable Geopolymer Concrete Using Recycled Coarse Aggregate and Ultrafine Slag at Ambient Curing

This study aimed at investigating the durability characteristics of the ambient-cured geopolymer concrete (GPC) developed using recycled coarse aggregate (RCA) and ultrafine slag (UFS). Two series of mixes were prepared. Natural aggregates (NAs) were replaced by RCA at different volume levels of 0, 25, 50 and 100% in both series. Meanwhile, UFS was added as a replacement by volume of fly ash at varying levels of 0, 15, and 30% in the first series, while UFS was used in addition to fly ash by percentage weight of fly ash at the levels of 0, 15, and 30% in the second series. The compressive strength, water absorption, chloride ion penetration, and carbonation depth of the developed ambient-cured GPC were studied. In addition, creep and drying shrinkage of the specimens were also examined. It was found that the compressive strength increased with the UFS content, while the opposite trend was observed with increasing RCA%. The highest compressive strength obtained with 100% RCA was 40.21 MPa (at 90 days), when 30% UFS was used in addition to fly ash. The addition of UFS not only helped in improving the strength characteristics but also provided an alternative to heat curing, which is a major drawback of GPC. Furthermore, the negative effects of RCA can also be minimised by adding UFS, which can be used as a compensator to RCA to improve the durability characteristics. The experimental results prove that susceptibility to chemical, water and chloride attacks can be mitigated by incorporation of UFS, and durable GPC can be produced by using RCA and UFS.