Effect of mineral admixtures on alkalinity and strength of cement pore solution and its mechanism

The effects and types of mineral admixtures, such as fly ash and mineral powder, on the alkalinity and strength of the composite cement slurry pore solution at different curing ages are studied by comparative analysis, the composition and microscopic morphology of hydration products of hardened cement pastes of different curing ages are characterized and revealed by SEM, XRD, TG and other technical means.The results show that the incorporation of mineral admixtures reduces the alkalinity coefficient of the composite cement slurry.With the increase of the dosage, the alkalinity continues to decrease, and the 28 d alkalinity coefficient is about 12.2, which is 0.8 lower than that of the pure cement system, and the strength do not decrease significantly.At the same dosage, the alkalinity of pore solution of fly ash cement composite system is lower than that of slag cement composite system.The reason is that the incorporation of fly ash and mineral powder reduces the amount of Ca(OH)₂ produced in the composite cement slurry, which reduces 54% and 32% respectively after 28 d of curing, and generates a part of the C—S—H gel hydration with low Ca/Si product.