Effect of ingredients adding sequences on rheological properties of alkali-activated slag paste

Alkali-activated slag is a promising alternative to ordinary Portland cement. It is characterized by low carbon emission and superior mechanical properties compared to conventional OPC mixtures. However, the rapid setting time and short fresh properties life of AAS are major drawbacks and barriers halting its wide acceptance in the construction sector. The hydration for AAS is initiated as slag particles start to dissolve in the alkaline environment created by the used activator. Therefore, this study investigated the effects of powder activator (i.e., sodium meta-silicate) dissolving rate and consequently the increase in the alkalinity on the initiation of the hydration process. The effects of various adding sequences for ingredients (i.e., water and powder activator) on the workability and rheology behavior of AAS at constant water/binder ratio were explored. Results emphasized the role of powder activator concentration in accelerating the slag particle dissolution and losing workability. Adding the water to the slag showed slower hydration progress than adding the water to a mixture of slag and powder activator. The findings will narrow the gap related to selecting the convenient sequence of adding ingredients when conducting alkali-activated materials to assist in situ applications.