Effect of different activations of supplementary cementitious materials on the early-age compressive strength of mortars based on quaternary binders

Abstract

In recent years, building materials have seen the widespread use of supplementary cementitious materials (SCMs) due to important environmental considerations. However, most SCMs exhibit slow development of compressive strength in the early stages. This study aims to evaluate and compare three combined activation strategies of SCMs, namely natural pozzolana (NP), blast furnace slag (BFS) and limestone filler (LF), incorporated with a replacement level of 50% of cement. SCMs activation was achieved through three approaches: mechanical (grinding to Blaine fineness values of 3800 and 6000 cm²/g), thermal (curing at 20 and 40 °C), and chemical (addition of 1% NaOH by mass of binder). Early compressive strength (2 and 7 days) was measured and analyzed using a fractional factorial design. The results demonstrate that all investigated combinations of SCM activations generate synergistic effects by significantly improving the mechanical performance of early-age quaternary mortars, due to an acceleration of hydration reactions and an improvement in the densification of the material's microstructure. Statistical analysis (ANOVA) revealed that curing temperature is one of the most influential parameters on early compressive strength. Increasing the temperature from 20 to 40°C accelerates hydration and pozzolanic reactions, thus promoting faster calcium silicate hydrate C-S-H gel formation and a significant improvement in strength gain. Furthermore, the binder composition and the degree of substitution of SCMs strongly influence mechanical performance. Formulations containing adequate proportions of BFS and NP exhibit higher reactivity during activation.