Control over cement setting through the use of chemically modified fly ash

The controlling of setting time for cement/ fly ash mixtures obtained by treating fly ash with a dilute CaCO3 solution was investigated. The amount of material added to the fly ash is less than 0.06 wt % total mass of cement and fly ash which results in the modification of the physical and mechanical properties of cement slurry which includes workability, strength, shrinkage, porosity, and permeability. The performance of the CaCO3 treatment appears to be a result of each fly ash particle being provided with the necessary Ca prior to hydration without being dependent on cement-fly ash particle interactions. The results show that the setting curve for a typical typical cement may be altered to almost an ideal inhibition curve through a simple treatment with a low concentration CaCO3 solution.