Investigations on Pastes and Mortars of Ordinary Portland Cement Admixed with Wollastonite and Microsilica

Wollastonite is abundantly available in Rajasthan, Tamil Nadu, Uttarakhand, and Andhra Pradesh states of the Indian Union as a low-cost material. In this study, investigations were made on pastes and mortars to evaluate its potential as a new material for admixing with ordinary portland cement with or without microsilica. Its physical and chemical properties were analyzed. Wollastonite consists of 45.6% of CaO and 48% of ${\text{SiO}}_2$ , mostly in amorphous form. It has an average specific surface area of $842.7{\text{m}}^2/\text{kg}$ and retention on 45-micron sieve of 3.20%. When ground to fine powder, it attains an average particle size of 4 microns which is about 4.5 times finer than ordinary portland cement. Scanning electron microscope images show that wollastonite particles were solid, acicular in shape, and have rough surfaces. Several cementitious mix proportions of ordinary portland cement, wollastonite, and microsilica were investigated for normal consistency, initial and final setting time of paste, and compressive strength of mortar. Test results indicate that the mortar, which contains 82.5% cement, 10% wollastonite, and 7.5% microsilica, as cementitious material attains the highest compressive strength. The mortar, which contains 77.5% cement, 15% wollastonite, and 7.5% microsilica, as cementitious material achieves compressive strength higher than the conventional OPC mortar along with rendering maximum cement replacement for better economy of concrete work. It was observed that the compressive strength of mortar varied logarithmically with the days of moist curing and linearly with the proportion of admixing. Suitable predictive models are presented accordingly.