Bio-stimulation of sand-indigenous urease- and CA-producing bacteria for sustainable calcite-based bio-cementation and mechanical performance evaluation

Despite the growing interest in bio-stimulation for soil improvement, its application in cementitious materials remains limited. This study investigates the feasibility of stimulating the indigenous microbial community naturally associated with the sand to promote ureolytic and carbonic anhydrase (CA)-mediated mineralization and enhance mortar performance without bacterial isolation, cultivation, or encapsulation. Bio-stimulated sands were incorporated into mortar mixtures and evaluated by compressive strength, ultrasonic pulse velocity, water absorption measurements, and field emission scanning electron microscopy–energy-dispersive X-ray spectroscopy (FESEM–EDS) analyses. The results confirmed that bio-stimulation effectively promoted in situ calcite precipitation and improved the mechanical properties of mortar. The highest compressive strength was achieved by mix AR, reaching 31.29 MPa at 7 days, representing a 34.25% increase over the control (W) and 43.08 MPa at 28 days, representing an 11.61% increase. The CA-mediated treatment increased 7-day compressive strength by 24.31%, demonstrating performance comparable to that achieved through the conventional ureolytic pathway. UPV measurements indicated a denser internal microstructure in bio-stimulated mortars, while FESEM–EDS analyses verified the formation of well-developed biogenic calcite crystals on sand particles and within the mortar matrix. Sterilized specimens (A′, B′ and D′) exhibited no comparable mineral precipitation, supporting the role of indigenous microorganisms in the bio-cementation process. X-ray diffraction (XRD) analysis confirmed the formation of calcite in the bio-stimulated mortar, providing mineralogical evidence of bio-mediated precipitation. The proposed bio-stimulation approach provides a cost-effective, and environmentally sustainable strategy for improving mortar through calcite precipitation. CA-mediated mineralization also shows potential as an alternative to conventional ureolytic pathways for bio-cementitious applications.