Evaluation of Temperature Effects on Microbially Induced Carbonate Precipitation (MICP) Stabilization of Subgrade Soils

Abstract

Ontario’s cold climate, characterized by temperature variations and freeze–thaw cycles, challenges pavement subgrade stability. Weak or unstable subgrade soils contribute to alligator cracking, rutting, and frost heaving, requiring conventional additives such as Portland or GU cement. This study investigates alternative treatment approach: Microbially Induced Carbonate Precipitation (MICP), a biogeochemical process in which urease-producing bacteria induce calcium carbonate precipitation to bond soil particles. MICP performance under cold-climate curing and repeated freeze–thaw exposure remains insufficiently understood. This research evaluates MICP on subgrade soil from Highway 401. Sporosarcina pasteurii was used in MICP treatment with a urea–calcium chloride cementation solution; samples were cured at 4°C, 10°C, and 20°C to represent subsurface conditions and tested before and after 12 freeze–thaw cycles. Performance was evaluated using Unconfined Compressive Strength (UCS), and MICP calcium carbonate content was quantified through acid washing. The study examines curing-temperature effects and freeze–thaw durability, providing insight into environmentally friendly cold-region subgrade stabilization and evaluates MICP performance using EMC² as the benchmark. MICP produced measurable cementation and a usable range of UCS values even at 4°C, the coldest curing condition tested, showing that MICP-based stabilization is mechanically achievable under cold curing. Freeze–thaw cycling was the more serious limitation, with none remaining a coherent, testable specimen by the end of cycling. In terms of strength, MICP-treated specimens reached only about 37–51% of the UCS achieved by EMC²-treated specimens under equivalent curing conditions. Together, these results suggest MICP is a technically viable, lower-carbon stabilization approach for Ontario subgrade soils under cold curing, but that its freeze–thaw durability, as tested, limits its suitability for long-term or repeated-cycling exposure without further development.