Comparison of unitary and hybrid cement systems activated with acid and alkaline solutions

Abstract In parallel with the alkaline activation of aluminosilicates, acid activation takes place. Often less studied, the so-called phosphate-based geopolymers are little publicized due to the concerns that arise during their manufacture. However, they are presented as materials with greater mechanical strength and greater chemical stability than alkaline activations. Thus, their applications are not as simple as forming structural parts, but in specific applications that do not require an integral core. The acidic and alkaline activation of metakaolin and fly ash was evaluated in the fresh and hardened state using calorimetry, mini-slump, rotational rheology and compressive strength. For unitary systems, acid activation presented greater compressive strength than alkaline activation. However, for hybrid systems there was a limitation in the incorporation of fly ash, which, over time, favored the mechanical behavior of alkaline systems over acids systems.