Comparative effects of limestone and fly ash on hydration, rheology, and strength of blended cements

To evaluate and compare the effect of calcite on different binder systems, four distinct mixtures were prepared and tested up to 90 days of curing. The incorporation of calcite led to reduced flowability, whereas fly ash improved it. In Portland cement, the reaction products were ettringite, monocarbonate, Ca(OH)2, and C–S–H. The incorporation of calcite, fly ash, or both led to increased monocarbonate formation. However, the pore-filling effect attributed to monocarbonate was masked by the dominant physical influence of calcite. The calcite in this study contributed through both chemical and physical mechanisms within the cementitious system. Although the pore-filling effect of calcite was significant, it did not surpass the pore-refining effect resulting from the pozzolanic reaction of fly ash. The incorporation of calcite into Portland cement resulted in a reduction in compressive strength, primarily because of a dilution effect.