Strength, sorptivity and carbonation in blended OPC-GGBS, alkali activated slag, and fly ash based geopolymer concrete

Several studies have shown that alkali activated binders can achieve similar strengths to both ordinary Portland cement (OPC) and blended cements. However, to date little research has been undertaken on their durability properties. This study investigated the influence of activators concentration and alkali modulus on strength, sorptivity and carbonation of alkali activated slag (AAS) and fly ash (FA) based geopolymer concrete. The same tests were also conducted on blended concrete with 30%, 50%, and 70% OPC replacement with ground granulated blast-furnace slag (GGBS) along with control concrete. Results indicate that the alkali modulus has a major effect on sorptivity of both AAS and geopolymer, however no significant effects of the alkali modulus on carbonation was observed on AAS concrete. The phenolphthalein indicator gave no clear indication between carbonated and non-carbonated area in geopolymer specimens. The sorptivity of blended concrete reduced but Ihe carbonation increased as the replacement level increased.