Effect of sulfate-rich sewage sludge ash and superabsorbent polymer on the crack resistance and environmental impacts of self-leveling mortars

In order to promote the recycling of sulfate-rich sewage sludge ash (SR-SSA), it was tried to use SR-SSA in cement-based self-leveling mortars (CSLM) with superabsorbent polymer (SAP). The effects of SR-SSA and SAP on fluidity, compressive and flexural strength, drying shrinkage and cracking resistance of CSLM were studied. The environmental and economic analysis on CSLM with SR-SSA were also performed. The presence of SR-SSA and SAP lowed the fluidity, flexural and compressive strength of CSLM. When 10% SR-SSA and 0.04%SAP were added together, the fluidity of CSLM was still higher than 130 mm, but the 90d flexural and compressive strength were reduced by 15.5% and 16.4% respectively. When SR-SSA and SAP were added, the drying shrinkage of CSLM was lowered, and the cracking resistance of CSLM was improved. The addition of 10% SR-SSA and 0.04% SAP reduced the drying shrinkage of CSLM by 25.9%, postponed the initial cracking time by 102 mins, reduced the cracks number by 3, reduced the average crack area by 27.4% and the total crack area by 47.4%. SR-SSA and SAP showed a synergistic effect on drying shrinkage reduction and cracking resistance improvement of CSLM. More ettringite was formed in CSLM when SR-SSA and SAP were added together. The addition of SR-SSA lowered the environmental impacts and raw materials costs of CSLM. When 10% SR-SSA and 0.04% SAP were added, the global warming potential, acidification potential, and eutrophication potential were reduced by 7.53%, 2.96% and 3.30%, respectively, and the raw materials cost of CSLM was reduced by 15.5%. The results of this study can provide a new way for the sustainable utilization of SR-SSA in CSLM.