Influence of granulated blast furnace slag and silica fly ash on the hydration kinetics of multi-component cements

Abstract The study investigates the influence of granulated blast furnace slag (GGBFS) and silica fly ash (FA) on the hydration kinetics of multi-component cements with different proportions of these components. Four model binders were analyzed, including reference alite cement and three composite systems with varying shares of GGBFS and FA. Microcalorimetric tests confirmed that replacing clinker with mineral additives significantly decreases the total heat of hydration up to 50% after 168 h compared to pure alite cement. The results also indicate a clear extension of the induction period and a delayed occurrence of maximum heat release, depending on the slag-to-ash ratio. Thermogravimetric analyses (TG/DTA) showed that the introduction of slag and fly ash reduces portlandite content in hardened pastes while increasing the share of the C–S–H phase, particularly between 28 and 90 days of curing, which demonstrates a synergistic hydraulic–pozzolanic effect. These findings confirm that multi-component cements with high slag and fly ash contents meet the requirements for low and very low heat cements and, in addition to ecological benefits such as significant CO 2 reduction, offer improved durability, lower susceptibility to chemical attack, and suitability for massive concrete structures.