Thermal and mechanical performance of concrete pavement dosed with calcined water treatment plant sludge

Abstract This study aimed to investigate the mechanical and thermal performance of concrete pavement with partial replacement of Portland cement by calcined sludge ash from a water treatment plant (WTP). In addition, this study also evaluates the physical and chemical characteristics of the WTP calcined sludge originating from southern Brazil. The research methodology was conducted in four stages: the characterization of raw materials; concrete dosing study with different levels of WTP sludge replacing cement (0, 1, 5, and 10%), assessment of the mechanical and thermal properties and microstructural analysis of the concrete mixtures in the hardened state, and statistical analysis. The characterization tests showed that WTP sludge is a non-hazardous and non-inert waste. The WTP sludge calcined at 800°C for 2 h has great potential to be used as a pozzolan in cementitious matrices. Laboratory results showed that the mechanical properties of hardened concrete mixtures increased with increasing WTP sludge content. However, through statistical analysis, it was possible to verify that the percentage of 10% of WTP sludge best contributed to the increase in the mechanical performance of the concrete mixtures. Regarding the analysis of the thermal properties of concrete mixtures, it was found that the percentage of 10% WTP improved the thermal conductivity, contributing to the lowest temperature variation of the material. Scanning electron microscopy (SEM) analysis demonstrated that adding the sludge (up to 10%) did not change the material's pore structure. Finally, this research indicated that the use of 10% WTP sludge as a partial replacement for Portland cement in concrete pavement improved its mechanical and thermal properties.