Effect of Temperature on pH, Conductivity, and Strength of Lime-Stabilized Soil

Lime is often used to increase strength, reduce compressibility, and reduce moisture sensitivity in soils with moderate to high plasticity. In the case of road construction, state agencies typically have specifications that prevent lime stabilization of subgrade soils during low temperatures (e.g., $<4°\mathrm{C}$). Part of the rationale for these specifications is that lower curing temperatures reduce the kinetics of pozzolanic reactions, which in turn may prevent the design strength from being reached. The objective of this research was to investigate the effect of temperature and time on reactivity and strength for lime-soil mixtures. The pH, electrical conductivity, and unconfined compressive strength of soils mixed with varying lime contents were respectively measured at various curing temperatures at multiple curing periods. Results indicate that increased curing duration leads to decreases in pore fluid pH and conductivity. However, this reduction in pH is less at temperatures below 10°C, which indicates lower levels of reactivity. Increased lime is recommended for situations in which stabilization will proceed at cooler temperatures. Unconfined compressive strength does not significantly increase with curing duration until after 7 days, after which the effect of pozzolanic reactions is evident. The trend of increasing unconfined compressive strength with increasing temperature was observed for both short- and long-term curing durations. The 7-day cured sample strengths at 2°C increased by 10% when allowed to cure for 56 days, while the samples cured at 21°C increased by 100% with the same curing duration. Exposure to either freeze-thaw cycles or low curing temperatures (2°C) resulted in significant reductions in strength gain for a given curing duration. However, once the freeze-thaw cycles or temperature reduction was removed, strength gain resumed at approximately the same rate. Overall, these results suggest that current specifications may be modified to allow lime stabilization to proceed in lower temperatures, if a corresponding increase in curing time and/or thermal protection is provided.