Compressive strength, pore structure, and hydration products of slag foam concrete under sulfate and chloride environment

In this study, blast furnace slag (BFS) was used instead of partial complex Portland cement (PC) to produce slag foam concrete (SFC), aiming to improve the ion attack resistance and compressive strength of nature foam concrete (NFC). The behavior of compressive strength, pore structure, hydration products, and microstructure of SFC in salt environments (5% Na2SO4, 5% NaCl, 5% Na2SO4+5% NaCl) was investigated. The findings indicate that the negative effect on the compressive strength of sulfate is mitigated by chlorine. In NFC, the loss of compressive strength in the Na2SO4, Na2SO4+NaCl, and NaCl solution at 120 days is 18.06%, 12.28%, and 3.58%, respectively. The optimization of SFC by the addition of BFS first increases with the amount of replaced cement until the positive effect of BFS is overshadowed by its negative effect when the amount replaced reaches 50%. And the salt erosion resistance of SFC with 30% of cement replacement is the best of all mixtures with KSO2and KSO2-4 +Cl- of 0.89 and 0.94 respectively. In the beginning, the SO2-4 and Cl- promote the production of more ettringite (AFt) in the SFC, which results in the filling of the original cracks and a reduction in pore volume. The opposite situation gradually occurs in SFC owing to the expansion of the AFt, as salt curing continues. The content of hydration products varies according to the amount of BFS added, and a decrease in Ca(OH)2 and an increase in the gel are observed in SFC with 30% -50% of cement replacement compared to NFC.