Functionalizing heavy metal contained incinerated sewage sludge ash in recycled glass-based alkali-activated materials for sewer environment

This study evaluates the performance of alkali-activated cement (AAC) mortars in an artificial sewage environment. The mortars, initially prepared with waste glass powder (GP) and ground granulated blast furnace slag (GGBS) in a 50:50 mass ratio, were modified by replacing 10 wt% of GGBS with incinerated sewage sludge ash (ISSA) with the goal of offering a biocidal effect. Comparisons were made with calcium aluminate cement (CAC), metakaolin (MK), and MK combined with zinc ferrite nanoparticles, each at a similar GGBS replacement level. The results showed that only incorporating CAC improved the strength development, achieving compressive and flexural strengths of 62.7 MPa and 7.4 MPa, respectively, at 28 days, while introducing ISSA or MK reduced the compressive strength to 47 MPa and flexural strength to 4.5 MPa. Although heavy metal ions from ISSA or zinc ferrite nanoparticles minimized biofilm thickness, they could not compensate for the reduced strength and increased alkalis leaching. Among all the tested mixtures, the 50GP40GGBS10CAC mixture exhibited superior biogenic acid resistance, possibly due to its Al-rich C-N-A-S-H gel phases (Ca/Si = 0.4, Na/Al = 0.8, Si/Al = 3.4) and refined pore structure (porosity = 3.4 %), making it the most microbial acid-resistant option for sewer rehabilitation.