Review and Experimental Investigation of Retarder for Alkali-Activated Cement

Alkali-activated cement (AAC) cured at ambient temperature conditions have a wider application area compared to heat cured AAC. High calcium precursor materials such as ground granulated blast furnace slag (GGBS) are commonly used to achieve ambient curing behavior. However, the GGBS results in a short setting time. Hence setting adjustment is critical in such AAC systems. This paper reviews state-of-the-art in the area of retarders for AAC systems. The most promising prospective retarders such as zinc salts, borax, sucrose, and phosphates are investigated. The retarder’s effect is dependent on the precursor materials and alkaline activators used. Consequently, in the review, these are identified for each retarder discussed. Some of the retarders were then tested in AAC with a blended precursor system containing fly ash (FA) and GGBS activated with sodium hydroxide and sodium silicate. The results showed that each borax percentage, with respect to the total solid binder, increases the setting time by about 50% of the mix without borax. Sucrose, sodium acetate, acetic, and phosphoric acids have no significant effect on the investigated AAC’s setting time.