Investigation of microstructural properties of high volume fly ash blended cement mortars including micronızed calcite

The hardened and microstructural properties of cement mortars containing high volumes of fly ash were investigated depending on the variables of micronized calcite and fly ash. For this purpose, twelve mixtures with different fly ash to cement ratio and micronized calcite replacement levels of 0.0, 0.25, 0.54, 1.0 and 0%, 2.5%, 5%, respectively, were designed. In order to evaluate the hardened property and microstructural characteristics at different curing ages, compressive strength, ultrasonic pulsive velocity test, and scanning electron microscopy analysis were performed. The experiment results showed that a significant improvement was obtained in early-age hardening properties in the mixtures including micronized calcite (especially in mixtures produced with a combination of fly ash and micronized calcite). On the other hand, the test results of hardened properties were confirmed by SEM images. Although a decrease in early-age compressive strength was achieved with the increase in fly ash replacement, as a result of nucleation and chemical action mechanisms higher results were obtained at the 90-day compressive strength comparing to the control mixture. The 90-day compressive strength values of the control mixture without micronized calcite and cement mortars containing 35% fly ash and 2.5% micronized calcite were 43.2 MPa and 51.9 MPa, respectively. Therefore, higher replacement level of fly ash and also a combination of calcite and fly ash resulted in a higher reduction in the carbon footprint of cement.