Influence of raw material properties on microscopic and mechanical characteristics of alkali-activated materials

Alkali-activated fly ash and slag pastes are considered a new low-carbon cementitious material with good mechanical characteristics and durability. However, the mechanical characteristics of the alkali-activated materials are uncertain due to the multiplicity of the raw material properties. Few studies clarify how the raw material properties affect the mechanical characteristics of hardened pastes. The correlation between the raw material properties and the reaction rate, product composition, gel content, and pore size distribution is discussed in this study. The increase in the CaO content of the precursor will accelerate the degree of alkali activation. In this case, the reaction production becomes relatively more, and the pore size distribution becomes relatively denser, improving the compressive strength of the pastes. Moreover, the effects of the activator modulus and alkali content on the compressive strength of the pastes are not monotonically increasing. The excessive alkali will cause the surface of raw material particles to form a gel layer quickly, which could prevent the further alkali activation of the particles. This case is not conducive to gel formation and will cause the pore structure of the hardening pastes to be relatively loose. Furthermore, the influence of activator modulus on the compressive strength of pastes is lower than that of alkali content. Excess activator modulus is also unfavourable for pore structure densification.