EVALUATING THE IMPACT OF AMMONIUM BYPRODUCTS FROM MICROBIAL-INDUCED CALCITE PRECIPITATION ON ATTERBERG LIMITS OF STABILIZED CLAYEY SOIL

Abstract

This study investigated the release of ammonium (NH₄⁺) byproducts during microbially induced calcite precipitation (MICP) and their impact on the Atterberg limits of treated clayey soil. MICP enhances soil strength and reduces permeability; however, its byproducts can influence soil properties, especially in clayey soils. This research examined the effects of NH₄⁺ ions from MICP on clayey soil’s plastic limit (PL) and liquid limit (LL) under varying curing times. PL, LL, and soil microstructure changes were analyzed using Atterberg limits tests, pH measurements, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Four treatment cases were evaluated: untreated clayey soil (control), clayey soil combined with calcite powder, clayey soil mixed with (NH₄)₂CO₃ and CaCl₂ solutions, and clayey soil mixed with an NH₄Cl solution. The results demonstrated that NH₄⁺ contamination significantly increased the PL and LL values by approximately 39.5% and 27.1%, respectively, due to enhanced water absorption capacity. In contrast, adding calcite powder decreased the PL and LL values by approximately 6.05% and 18.69%, respectively, compared to untreated clayey soil. NH₄⁺ ions reduced pH levels from an initial value of 5.0 to 4.2, whereas calcite addition raised pH to 8.1. With increased curing time, PL, LL, and pH values stabilized for all cases. SEM analysis indicated the presence of calcite particles in treated soils at 1 and 28 days, suggesting rapid calcite precipitation. FTIR results confirmed that NH₄⁺ remained stable over time, supporting the constancy of PL, LL, and pH across all treatments. These findings have significant geotechnical engineering implications, particularly for soil stabilization using MICP in construction applications, where NH₄⁺-induced plasticity may affect soil compaction and strength. Proper management of NH₄⁺ byproduct is essential to ensure the long-term performance of MICP-treated clayey soils.