Cement companies are significant contributors of the planet’s anthropogenic CO2 emissions.
With increased awareness of the substantial volume of CO2 emissions from cement production, a
variety of mitigation strategies are being considered and pursued globally. Hybrid cements are
deemed to be technologically viable materials for contemporary construction. They require less
clinker than that for ordinary Portland cement, leading to a decrease in CO2 emissions per tonne of
hybrid cement manufactured. The hybrids produced in this study consist of 70% siliceous coal fly
ash and 30% Portland cement, and combines chemical (sodium sulphate) and mechanical (milling)
activation. The aim of this work was to develop a better understanding of the hydration products
formed and the resulting effect of activation on these hydration products, of hybrid coal fly ash cement
pastes over an extended curing period of up to one year. The results indicated that chemical activation
increases the formation of stable, well crystallised ettringite. Chemical activation as well as mechanical
activation increased the rate of the pozzolanic reaction between portlandite contained in cement and
coal fly ash. The application of combined chemical and mechanical activation definitely resulted in
the fastest rate of portlandite consumption, hence an increased rate of the pozzolanic reaction.