In situ concrete sewer performance: comparison of Portland cement, calcium sulfoaluminate cement, and calcium aluminate cement

Abstract

This paper provides a better understanding of the performance of calcium sulfoaluminate cement (CSA) in comparison with calcium aluminate cement (CAC) and Portland-limestone cement, CEM II A/L 52.5 N (CEM II) in live sewer environments. Three concrete mixes using these binders, with 0.34 w/b, siliceous pit sand, and dolomite aggregates, were prepared for two years of exposure in two sewer sites. During exposure, monitoring through visual observation, concrete surface pH, mass and thickness change was conducted regularly to observe the deterioration. At the end of exposure, microstructural analysis, i.e., Scanning Electron Microscopy, Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN) and XRD analyses, were conducted to elucidate the deterioration mechanisms further. Regardless of sewer exposure conditions, the monitoring results indicated that CAC concrete had superior performance, followed by CSA, then CEM II. However, corrosion rates were accelerated when a sewer had hydraulic actions and high H2S gas concentrations (max.>300 ppm). CSA outperformed CEM II due to the presence of ettringite, while ettringite superposition in the transition zone reduced CSA performance compared to CAC concrete. Binder performances wereprimarily related to their chemistry, mineralogy, and interaction with aggregates.This paper provides a better understanding of the performance of calcium sulfoaluminate cement (CSA) in comparison with calcium aluminate cement (CAC) and Portland-limestone cement, CEM II A/L 52.5 N (CEM II) in live sewer environments. Three concrete mixes using these binders, with 0.34 w/b, siliceous pit sand, and dolomite aggregates, were prepared for two years of exposure in two sewer sites. During exposure, monitoring through visual observation, concrete surface pH, mass and thickness change was conducted regularly to observe the deterioration. At the end of exposure, microstructural analysis, i.e., Scanning Electron Microscopy, Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN) and XRD analyses, were conducted to elucidate the deterioration mechanisms further. Regardless of sewer exposure conditions, the monitoring results indicated that CAC concrete had superior performance, followed by CSA, then CEM II. However, corrosion rates were accelerated when a sewer had hydraulic actions and high H2S gas concentrations (max.>300 ppm). CSA outperformed CEM II due to the presence of ettringite, while ettringite superposition in the transition zone reduced CSA performance compared to CAC concrete. Binder performances wereprimarily related to their chemistry, mineralogy, and interaction with aggregates.