Investigation of the properties of composite binders for cement mortar

This study investigates the rheological, structural-mechanical, and strength properties of composite cement-based binders containing finely dispersed mineral fillers, including limestone, zeolite-containing rock, and microsilica. The effects of cement content in the range of 10–50% on water demand, yield stress, setting time, and 28-day compressive strength were experimentally evaluated at comparable mixture plasticity. The results showed that water demand strongly depended on the type of mineral filler, with microsilica-containing compositions requiring the highest water-to-solid ratios and limestone-containing compositions the lowest. Increasing the cement content reduced the water-to-solid ratio, decreased yield stress, and accelerated both initial and final setting. The yield stress–cement content relationships were satisfactorily described by exponential regression models, with coefficients of determination of 0.971-0.998. At comparable plasticity, the 28-day compressive strength ranged from 7.4 to 48.6 MPa, with the highest values obtained for limestone-containing compositions, followed by zeolite-containing and microsilica-containing compositions. Linear regression models were used for preliminary selection of cement content to achieve a target compressive strength. For a target strength of 25 MPa, the calculated cement contents were approximately 26.3 %, 29.8 %, and 46.5 % for limestone-, zeolite-, and microsilica-containing binders, respectively. The results provide a basis for rational selection of composite binder compositions for masonry and plaster mortars using local mineral raw materials.