Recycling use of sulfate-rich sewage sludge ash (SR-SSA) in cement-based materials: Assessment on the basic properties, volume deformation and microstructure of SR-SSA blended cement pastes

Abstract

Sewage sludge ash (SSA) is the waste obtained from the incineration of wastewater sludge. SSA could be recycled in cement-based materials, but normally SSA in China is sulfate rich, and how the sulfate-rich sewage sludge ash (SR-SSA) influence the properties and microstructure of cement-based materials is still unknown. This study aimed to investigate the possibility of recycling use SR-SSA in cement-based materials. The effect of SR-SSA on the basic properties, volume deformation and microstructure of the cement paste was experimentally studied. The findings of this study indicated that the addition of SR-SSA reduced the workability, compressive strength and flexural strength, retarded the setting times, reduced the autogenous shrinkage and caused greater long-term drying shrinkage and higher potential expansion of the cement paste. The formation of excessive ettringite and the coarse pore structure contributed to the properties reduction and volume instability of cement pastes with excessive SR-SSA. However, replacing 5% cement with SR-SSA didn’t induce much detrimental influence on the properties of cement paste. It is feasible to recycle SR-SSA in cement-based materials by replacing up to 5% cement. At the same time, replacing 5% cement with SR-SSA could result in 4.98% lower CO2 emission and 25.42% lower financial cost. In case of recycling all SR-SSA in China, it is possible to expect annual reduction in CO2 emission of 6.8 billion kg CO2-e and financial cost of 16.1 billion RMB yuan. This study could help to recycle SR-SSA and improve the sustainability of cement-based materials.