Application of eco-friendly alternative activators in alkali-activated materials: A review

Alkali-activated materials are a new class of compounds that have been studied by several authors worldwide. Alkali-activated binders can be competitive alternatives to traditional Portland cement, especially concerning CO2 emissions into the environment. However, in order to obtain this advantage, it is essential to use activators that were produced cleanly and sustainably, which is not the case of commercial products such as NaOH or sodium silicate. This paper provides a brief discussion about the activators traditionally used, and a review of existing literature about alternative activators, produced from agricultural or industrial wastes. Factors such as molar ratios and preparation of the solution were highlighted. The mechanical behavior of the pastes and mortars was also assessed, showing that the performance of alternative activators can be similar or even better than the conventional ones. Finally, some topics for future research on new activators were identified, aiming to stimulate more studies in this field.