Thermodynamic and Kinetic Modeling of the Lime–Kaolinite System

Abstract

A thermodynamic and kinetic model of kaolinite mixed with 5% lime was developed in this study in order to inform the long-term prediction of the system composition and its influence on the geotechnical properties of lime-stabilized clays. For model calibration, pore solution analysis of lime–kaolinite-compacted monoliths was performed for up to 2 years of curing time. The model showed that there are three stages in the evolution of the pozzolanic reactions that correspond to a progressive decrease in the rate of kaolinite dissolution. In the first stage (0–180 days of curing), portlandite is consumed rapidly, and kaolinite dissolution proceeds at the highest rate. From the model prediction, the phase assemblage during this stage is amorphous jennite, C4AH13, and SO4-AFm, which control Al and Si in solution at very low values and result in rapid strength development. In the next stage (180–360 days), portlandite is consumed and kaolinite dissolution slows down. Si and Al in solution increase rapidly, and the phase assemblage shows transformation to stratlingite first and then a small amount of gibbsite and tobermorite-II also starts forming. The last stage is marked by a further decrease in the dissolution rate and transformation of stratlingite to tobermorite-II and gibbsite, with every component in the solution plateauing except Si, which is predicted by the model to increase. The phase transformation is related to a reduction in strength from 360 to 720 days of curing. The model also predicts a last drop in pH and Al when stratlingite is completely depleted and equilibrium is reached, which was not observed in the experiments terminated at 720 days.