Concerns around the CO₂ emitted in Portland cement manufacture have driven the scientific community to seek alternative materials with the same features as Portland cement but which can be sustainably manufactured. One such category of materials includes the blended or hybrid cements.

These cements form when blends containing low proportions of cement and high proportions (60-70 %) of mineral additions (slag, fly ash or metakaolin) are alkali activated. This article reviews the fundamental chemistry governing these new reactive systems. It also analyses the nature of the reaction products formed and their compatibility under different reaction conditions.