Durability assessment of bio-modified geopolymer concrete in simulated sewage environments

Abstract

Sewer infrastructure worldwide is ageing beyond its designed lifespan, rendering it increasingly vulnerable to biogenic sulphuric acid corrosion, cracking, and structural collapse. Geopolymer concrete represents a promising sustainable alternative to ordinary Portland cement in such aggressive environments; however, its durability under acidic conditions remains insufficiently characterised, particularly when combined with microbial modification. This study evaluated the sulphuric acid resistance and microstructural integrity of two fly ash-based geopolymer concrete formulations—a control mixture and a Shewanella oneidensis species-enhanced bio-modified mixture (Bio)—subjected to 1% H₂SO₄ immersion at 30 °C for 10 days to simulate sewer conditions. A multi-technique analytical framework comprising mechanical testing, capillary water absorption, SEM–EDS, XRF, FTIR, and XRD was employed to elucidate degradation mechanisms and quantify the effect of bacterial modification. Bio-modified specimens exhibited a denser, more homogeneous microstructure and markedly superior acid resistance, including an 82% increase in splitting tensile strength following acid exposure, in contrast to a 13% decrease recorded in control specimens. SEM–EDS analysis confirmed reduced cracking and enhanced retention of Ca and Fe in bio-modified specimens. XRD revealed the preservation of acid-resistant crystalline phases, including quartz and andradite, in bio-modified specimens, whereas the control specimens showed greater phase decomposition and decalcification. FTIR analysis indicated greater stability of Si–O–T bonds in bio-modified specimens, consistent with reduced silicate depolymerisation. These findings confirm that Shewanella-based bio-modification significantly enhances the durability of geopolymer concrete under sulphuric acid attack, supporting its application as a resilient and sustainable material for sewer infrastructure.