Properties of corn cob ash and effect on hydration kinetics in PC-blended cementitious systems

The study investigates the effects of the properties of calcined corn cob ash on the hydration kinetics of Portland cement (PC). The corn cob ashes were used at PC replacement levels of 15% and 30%. The materials were characterised for oxide composition and amorphous content using XRF and XRD respectively. The reactivity of the corn cob ashes was assessed using both the R3 Test (ASTM C1897-20) and the strength activity index (SAI). The hydration kinetics of the corn cob ashes was assessed using isothermal calorimetry at 20 °C with measurements taken up to 48 h. The results show that the corn cob ashes produced at the two temperatures are largely crystalline, showing little pozzolanicity even though the SAI indicated otherwise. Partial replacement of PC with corn cob ash affected the evolution of heat of hydration of PC, prolonging the induction phase and delaying the evolution of the main heat peak.