This paper discusses the performance of calcium sulpho-aluminate (CSA) cement and a Sulphate-Resisting Portland Cement (SRPC) with a fly ash (FA) additive (i.e., a SRPC + FA binder system) in a ‘live’ sewer environment; it deepens the understanding of their deterioration mechanisms by using a laboratory test for simulated sewer conditions. It also studies the role of an iron-based additive (‘Hard-Cem^®’, HC) in improving the performance of SRPC + FA concrete under a biogenic acid attack. The performance of 0.4 w/b concrete specimens of the three binders (CSA, SRPC + FA, and SRPC + FA + HC) with calcite aggregates in sewer exposure was assessed by visual observation, measurements of mass and thickness changes, and microstructural analysis for approximately 25 months. The laboratory test, i.e., the Biogenic Acid Concrete (BAC) test, was used to study the deterioration mechanisms of these binders in terms of leaching solution pH and standardised cumulative leached calcium and aluminium. The results indicate that CSA concrete had improved performance in the sewer environment, showing no mass loss and only about one-third of thickness lost in the SRPC + FA concrete over a 25-month exposure period in the sewer environment. The BAC test results complemented the field observations. The iron-based additive in sewer concrete slightly reduced mass loss, likely due to its better resistance to abrasion and erosion, but not due to any chemical influence, since it does not participate in hydration or dissolution reactions. The findings imply that CSA cement may represent a suitable alternative binder for concrete sewer construction. They also suggest that a surface hardener has limited benefits, except when it is under abrasive conditions. Further investigation is required, especially since CSA contains high amounts of sulphate, the effect of which is not well understood.

Precast concrete products are load-tested to confirm compliance, but the workability of the concrete, being generally zero-slump concrete, is often not tested for quality control, as would be done with normal- or high-slump concrete. An industry practice in South Africa uses the percussive action of a rotary percussion drill to compact control cube samples. However, variability in specimen compaction leads to variations in the density and compressive strength results, making the procedure unreliable. This indicates a need for a simple, standardised quality control method for preparing zero-slump concrete cube samples with compaction equivalent to that achieved by precast machines. This technical note aims to (i) report on a practical and economical procedure (i.e. percussion-drill method) that has been formulated for quality control based on the concrete density achieved by precast machines, and (ii) apply this method to mix optimisation with the specific objective of partial replacement of the cement in a factory mix with a suitable fine filler to reduce cost and the carbon footprint of a precast facility. It was shown that the percussion-drill method was able to obtain reliable results (density, compressive strength) for quality control purposes and was successfully employed in the replacement of 17% to 32% of cement by volume with quartz flour in a factory mix. This resulted in a significant cost saving and a reduction in nett carbon emissions at the factory.

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.