In line with Canadian low-carbon roadmaps, the cement and concrete sector need to reduce greenhouse gas emissions to achieve net-zero targets by 2050. As clinker production is the primary source of cement-related CO2 emissions, reducing clinker content through supplementary cementitious materials (SCMs) or limestone substitution, as in General Use Limestone (GUL) cement, is an effective strategy to lower embodied carbon while maintaining performance. Ground granulated blast furnace slag (GGBFS), an ironmaking by-product, can further reduce embodied carbon by up to 30% through partial cement replacement. Although the effects of carbonation on strength, shrinkage, and degree of carbonation (DOC) are studied, the influence of carbonation curing on volume stability and the underlying mechanisms in GUL-GGBFS materials remain unclear. This study investigated the volume stability and microstructural evolution of low-carbon cementitious materials incorporating GUL and GGBFS. Five mixtures with GGBFS replacement levels up to 80% were exposed to controlled drying (0.04% ± 0.001% CO2) and accelerated carbonation (3% ± 0.5% CO2). Compressive strength and shrinkage were measured up to 174 days, while mineralogical composition and pore structure were characterized using X-ray diffraction (XRD), thermogravimetric analysis (TG), X-ray computed tomography (XCT), and dynamic vapor sorption (DVS).
Results show that replacing 80% of cement with GGBFS reduced 28-day compressive strength by 66% compared with the mixture without GGBFS. Accelerated carbonation partially compensated for this strength loss: increasing GGBFS content from 0% to 40% led to a 47% strength gain due to pore structure densification. Regarding shrinkage, carbonation increased shrinkage by 50% in mixtures without GGBFS, whereas mixtures containing more than 40% GGBFS exhibited up to 20% lower carbonation-induced shrinkage. However, XCT analysis revealed that high GGBFS replacement levels (60-80%) promoted internal microcracking, adversely affecting strength and durability. Overall, accelerated carbonation provides benefits by increasing strength and CO2 uptake but introduces a shrinkage-related burden. This burden is effectively mitigated by 40% GGBFS replacement, highlighting the potential of a balanced GGBFS-carbonation strategy for developing volume-stable, carbon-neutral cementitious materials and support practical carbon capture and storage applications in construction.
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