Influence of Particle Size and Curing Temperature on the Strength of Sand Treated with Enzyme-Induced Carbonate Precipitation

This study investigates the effects of particle size and curing temperature on the compressive strength of sand treated with enzyme-induced carbonate precipitation (EICP). Three types of commercially available sands with distinct median particle sizes (coarse, medium, and fine) were used, along with a mixture of these sands, to examine how soil gradation influences biocementation. Samples were cured at two different temperatures, 4°C and 22°C, over 7- and 28-day periods. Sand samples cured at 22°C, room temperature, gained strength rapidly, showing significant increases by 7 days and further by 28 days. In contrast, samples cured at 4°C, cold temperature, developed strength slowly, with notable increases only after 28 days. The unconfined compressive strength (UCS) was observed to increase as the median particle size decreased at cold temperatures, suggesting that finer particles contribute more effectively to strength development. Microstructural analysis using scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis revealed different patterns of calcium carbonate precipitation and particle bonding. UCS testing indicated that room-temperature-cured samples exhibited brittle failure, while cold-cured samples showed ductile failure. At cold temperatures, smaller particles showed more carbonate precipitation, but this trend reversed at room temperature, suggesting that environmental factors like temperature can alter bio-mediated cementation mechanisms. The sand mixture with a broader range of particle sizes achieved the highest UCS, emphasizing the importance of particle gradation in EICP optimization for soil stabilization.