Development of low-temperature-curing geopolymers using optimized sodium carbonate from microbially induced calcite precipitation

The increasing demand for construction materials and the substantial carbon footprint associated with traditional cement highlight the urgent need for sustainable alternatives. Traditional geopolymers have shown promise due to their lower carbon emissions ; however, their widespread application is often limited by the requirement for high-temperature curing . This study presents a modified method that employs microbially induced calcite precipitation (MICP) to synthesize sodium carbonate (Na 2 CO 3 ). This approach addresses previous challenges related to ammonium byproducts and inadequate mechanical performance in construction materials. The synthesis of Na 2 CO 3 was optimized by adjusting the quantities of NaOH, the solution volume, alcohol-to-water ratios, and curing temperatures. Characterization techniques, including Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), X-ray Fluorescence (XRF), and X-ray Diffraction (XRD), confirmed that the synthesized Na 2 CO 3 achieved commercial-grade purity. The synthesized Na 2 CO 3 was utilized to prepare geopolymer mortars activated using a 2 M Na 2 CO 3 solution combined with 5 % calcium hydroxide (Ca(OH) 2 ), high-calcium fly ash, and sodium silicate (Na 2 SiO 3 ) at a 1:1 ratio relative to Na 2 CO 3 . Under these optimized conditions, the resulting geopolymer mortar exhibited a compressive strength of 34 MPa after 28 days of ambient curing, demonstrating performance comparable to conventional cement-based mortars. Additional analyses using SEM, Energy Dispersive X-ray Spectroscopy (EDX), and X-ray Photoelectron Spectroscopy (XPS) confirmed the formation of N-A-S-H and C-A-S-H gels, along with progressive microstructural densification over time. This innovative integration of MICP and geopolymer technologies offers a sustainable, low-energy approach to reducing CO 2 emissions in the construction industry. • Modified MICP produced pure Na 2 CO 3 with minimal ammonium byproducts. • MICP-derived Na 2 CO 3 effectively activated geopolymer mortar at ambient curing. • Optimal geopolymer (2 M Na 2 CO 3 , 5 % Ca(OH) 2 , 1:1 Na 2 SiO 3 /Na 2 CO 3 ) reached 34 MPa. • SEM, EDX, XPS confirmed formation of N-A-S-H and C-A-S-H binding gels. • Novel integration of MICP and geopolymer technology offers a sustainable cement alternative.