Effect of Cement Type and Water-to-Binder Ratio on k-value of Low-Calcium Fly Ash for Concrete Compressive Strength

Abstract

The present study assessed the effect of cement type and water-to-binder ratio (W/B) on the cementing efficiency factor (k-value) of low-calcium fly ash (FA) for the compressive strength of concrete in a chemical approach. The results indicated that the k-values increased with an increase in the FA reaction degree for each cement type. Despite the higher FA reaction degree in high-early-strength Portland cement (HSPC) paste, the k-value in the HSPC concrete was lower than that in OPC (ordinary Portland cement) concrete. For OPC concrete, a lower W/B has a higher k-value at the early ages mainly because of cement hydration that is enhanced by FA, and all the k-values increased significantly after 28 days due to the pozzolanic reaction of FA. A modified equation of portlandite consumption for the FA reaction assessment that considers the cement-hydration-enhancement effect was proposed to assess the FA reaction degree more appropriately than the conventional one.