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This paper studies the time dependence of corrosion resistance in belitic calcium sulfoaluminate (BCSA) cement concrete. BCSA is a hydraulic cement that sets rapidly and has a lower carbon footprint than portland cement (PC). Some studies suggest that BCSA concrete is highly susceptible to chloride-induced corrosion, but these claims are based on testing at 28 days. No later-age results have been reported. We con昀椀rm that BCSA cement concrete exhibits poor corrosion resistance when tested at 28 days, which can be attributed to an immature microstructure with weak resistance to chloride ingress and a pore solution that does not support passivation. We further show that corrosion resistance improves signi昀椀cantly as the BCSA system matures, achieving good corrosion resistance between 90 and 180 days. This improvement relates to the slow hydration of belite, which results in signi昀椀cant later-age microstructure re昀椀nement and probably alters the pore solution in a way that promotes or enhances steel passivation. 

This paper studies the alkali-silica reaction (ASR) in rapid-strength belitic calcium sulfoaluminate (BCSA) cement systems. Theoretically, its low alkalinity and high alumina content should make BCSA less prone to ASR than portland cement (PC), but little experimental evidence has been published, and the theorized mechanisms have not been examined critically. We examine this problem using expansion tests, microstructural analysis, and pore solution analysis. Accelerated expansion tests show increased expansion in BCSA mortars with reactive aggregates, but we argue that the test conditions are unsuitable for the cement. Long-term expansion tests show a significant reduction in expansion in BCSA mortars with reactive aggregates, but later-age measurements still exceed ASTM C1778 limits and microstructural investigations indicate ASR damage. Curiously, BCSA mortars with nonreactive aggregates also expanded significantly, but no ASR damage was observed. BCSA pore solutions had ten times more aluminum than PC and one-tenth as much calcium. While the pH was sufficiently high to initiate ASR, the alkali reserves can be half or less than in PC. Overall, BCSA cement is not immune to ASR, but it is more resistant than PC. This is mostly related to the lower alkalinity of the cement and, to a lesser degree, to the abundance of alumina and shortage of soluble calcium.