Performance of cement pastes containing sewage sludge ash at elevated temperatures

•Higher relative residual compressive strength showed in SSA blended cement pastes.•Heating energy enhanced the pozzolanic reaction between SSA and CH.•More gehlenite formed in SSA blended cement pastes to fill the pores at 900–1000 °C.•Lower pore structure coarsening extent showed in SSA blended cement pastes. Performance of cement pastes containing sewage sludge ash (SSA) at elevated temperatures was evaluated in the present work. SSA blended cement pastes were prepared and subjected to thermal treatment at 600–1000 °C. The residual compressive strengths were investigated and the related physical, chemical and microstructural evolution at elevated temperatures was measured by XRD, FTIR, DTA, MIP and SEM analysis. Results showed that the incorporation of SSA enhanced the high temperature resistance of cement pastes in respect of the relative residual compressive strength and the paste containing 10% of SSA (S10) exhibited higher residual compressive strengths than plain cement paste (S0). Elevated temperatures caused decomposition of the hydrate products, coarsening of the pore structures and generation of the cracks, which were responsible for the degradation of compressive strength of pastes. The heating energy enhanced the pozzolanic reaction between SSA and CH to strengthen the matrix of pastes containing SSA at elevated temperatures. In addition, the incorporation of SSA promoted more formation of gehlenite at 900–1000 °C and such phase can fill the pores in the matrix. Therefore, S10 exhibited lower extent of pore structure coarsening than S0 at elevated temperatures.