Abstract
This paper presents the results of a study on the effect of silica fume and fly ash on the properties of self-compacting concrete (SCC). Mineral additives were used as a partial replacement for cement at dosages of 5, 10, and 15% by binder mass. The properties of cementitious systems were evaluated using isothermal calorimetry to study hydration processes, scanning electron microscopy (SEM) for microstructure analysis, and rheological tests to determine the flow characteristics of cement mortar. The results showed that the incorporation of silica fume increases the viscosity and yield stress of the cement mortar, enhancing its structural stability. Fly ash also increases viscosity and yield stress but exhibits more pronounced thixotropic behavior, leading to structural instability at low shear rate gradients. Calorimetric studies revealed that silica fume accelerates the early stages of cement hydration, whereas fly ash, on the contrary, slows down hydration processes. Microstructural analysis confirmed that the addition of mineral additives contributes to the formation of a denser and more homogeneous cement matrix. The obtained results suggest that silica fume can be recommended as an effective additive for improving the structural stability of SCC, while fly ash is beneficial for enhancing thixotropic properties and strength development.