Activation of Portland cement blended with high volume of fly ash using Na2SO4

Increasing the replacement ratio of Portland cement clinker by supplementary cementing materials is one of the best strategies to reduce the impact of the cement and concrete industry on the environment. While fly ash is widely available particularly in developing countries where much of the construction activities are projected in the coming future, the replacement levels are limited to around 25–30% in practice owing to its low reactivity. This work studies the effect of sodium sulphate (Na2SO4) on the activation of Portland cement blended with 50 wt-% class F fly ash. Na2SO4 activation contributes to a significant strength increase both in the early and later ages. Flow table results indicate that mortar workability is improved. Mercury intrusion porosimetry after 28 days show considerable refinement of pore structure. An increase in the bound water content, cumulative heat release, ettringite content and reduction of portlandite and AFm content were measured.