Physical and mechanical properties of bio-modified geopolymer concrete employing bacteria

Geopolymer concrete (GPC) offers a sustainable substitute for ordinary Portland cement (OPC) concrete; yet, it has issues related to shrinkage and durability. Shrinkage in geopolymer concrete (GPC) has been reported to be 2–4 times more than that in OPC concrete, particularly when utilising calcium-rich precursors such as slag, which may further elevate the risk of corrosion in reinforced GPC. Biomineralisation, thoroughly studied in OPC concrete to enhance durability and self-healing, remains inadequately explored in GPC, particularly with the direct inclusion approach of bacteria and ambient curing conditions. This work examines the direct inclusion of bioproduct containing Shewanella oneidensis into GPC as a more straightforward alternative to encapsulation or carrier-based techniques. A total of 200 mL of bacterial solution was utilised to produce six cubes and six cylinders of GPC, which were cured at 15–17 °C in a laboratory environment. After 28-day period, bio-modified GPC exhibited enhanced homogeneity, a 13.1 % decrease in water absorption (from 3.06 kg/m2 to 2.66 kg/m2), and a 26.5 % reduction in porosity (from 5.99 % to 4.4 %), attributed to calcite precipitation resulting from bacterial biomineralisation. Despite a minor reduction in compressive strength (from 20.44 MPa to 18.43 MPa), SEM indicated a denser matrix and improved interfacial transition zone (ITZ), while XRD validated the formation of calcite and the better preservation of quartz structures. The findings indicate that bacterial incorporation can significantly enhance the durability and self-healing capabilities of GPC, mitigating critical performance constraints. This approach demonstrates potential for sustainable infrastructure necessitating reduced maintenance and improved service life, particularly in resource-constrained or ambient-cured conditions.