Speaker
Description
The cement industry is increasingly focused on reducing CO₂ emissions associated with concrete-based construction. Supplementary cementitious materials (SCMs) play a significant role in this context, with extensive investigations aimed at maximising their utilisation without compromising, and ideally enhancing, the strength and durability. However, measuring autogenous and drying shrinkage is particularly critical in the context of low-carbon mortars incorporating SCMs and low water-to-binder ratios.
An experimental campaign was conducted to investigate the autogenous and drying shrinkage of binary mortar mixtures containing silicon manganese (SiMn) slag, with cement replacement levels ranging from 50% to 90%, and ternary mortar mixtures incorporating both SiMn and ground granulated blast furnace slag (GGBFS), with cement replacement levels ranging from 50% to 70%. Autogenous and drying shrinkage strains were measured over a period exceeding 200 days and compared to a control system comprising 100% ordinary Portland cement (OPC). Microstructural and mineralogical analyses, including SEM and XRD, were conducted to understand the influence of SiMn slag on hydration kinetics, pore refinement, and phase transformations.
The results indicate that autogenous shrinkage strain decreases at early ages with higher cement replacement levels due to reduce of OPC and the slower reactivity of SiMn slag compared to OPC, delaying self-desiccation. However, at high replacement levels, refined pore structures contribute to increased capillary tension, which may lead to increase autogenous shrinkage over time. In contrast, drying shrinkage strain increases in both binary and ternary mortar. This effect further increases within the mortar as the replacement levels of cement increase, due to enhanced packing density and refined porosity resulting from the incorporation of SCMs. The SCMs contribute to higher capillary tension during moisture evaporation, which intensifies the drying shrinkage. Further, SCM systems exhibits reduce compressive strength at early ages make the matrix more susceptible to deformations caused by environmental moisture loss exacerbating drying shrinkage.
The findings highlight compatibility and the potential use of SiMn slag as a high-volume cement replacement material, to the development of low-carbon cement mortar, provided that shrinkage-related challenges are addressed through optimal replacement levels and curing strategies.
