Reduced-Density Granite-Based Geopolymer using Borosilicate Glass Microspheres for Low-Temperature Well Cementing

Summary While glass microspheres have been exercised in conventional cement systems, their behavior in rock-based geopolymer formulations is unknown, and their role in the geopolymerization process remains underexplored. Lowering geopolymer density is challenging, caused by its sensitivity to additional water, which can delay setting and strength development. Additionally, geopolymers typically require elevated temperatures to start setting, posing difficulties in low-temperature environments. To address these issues, glass microspheres were incorporated to reduce the density of a granite-based geopolymer while maintaining mechanical integrity at low temperatures (15–25°C); the water content was held constant to isolate the effect of microsphere addition. Experimental evaluations, including rheological properties, compressive strength, isothermal calorimetry, and scanning electron microscopy (SEM), demonstrated that glass microspheres reduced slurry density while maintaining adequate compressive strength after extended curing at 15°C. However, microstructural analysis revealed progressive microsphere degradation, likely from high-pH dissolution, even at low temperatures, posing a potential risk to long-term hydraulic sealability. These findings reveal a previously overlooked durability concern and highlight the trade-offs between weight reduction and long-term performance in granite-based geopolymer systems. This work advances the understanding of geopolymer-microsphere interactions and offers design considerations for alternative cementing materials under mild thermal regimes.