Pumicite-Based Geopolymer Optimization for Sustainable Soil Stabilization

Climate change poses a significant threat to all living beings, prompting governments to implement laws aimed at reducing carbon dioxide (CO2) emissions. Geopolymer cement has emerged as a promising alternative to ordinary portland cement (OPC) in recent years. This study focused on evaluating the effectiveness of geopolymer based on natural pumicite pozzolan, activated using a combination of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH), for sustainable stabilization of silty sand soil. The study used the response surface method (RSM) to assess various factors affecting unconfined compressive strength (UCS). Key parameters examined were pumicite content, the ratio of Na2SiO3 solution to NaOH solution, NaOH concentration, the ratio of alkaline activator solution to pumicite content, and curing age. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analyses were employed to study the formation of gels and the crystals formed. Results from the RSM analysis revealed that optimal strength is achieved with 20% pumicite by weight, a Na2SiO3 solution to NaOH solution ratio of 1.5, a 12-M NaOH concentration, and an activator solution to pumicite content ratio of 0.5. In addition, microstructure analysis indicated that the addition of pumicite results in the formation of key products—sodium aluminosilicate hydrate (NASH) and calcium aluminosilicate hydrate (CASH) gel. These products, originating from the reaction between pumicite and the alkaline activator solution, were identified as the primary contributors to the improved strength of the sample.