Analytical tests to evaluate pozzolanic reaction in lime stabilized soils

Area of Science:

• Geotechnical Engineering
• Materials Science
• Soil Science

Background:

• Shrink-swell soils pose significant engineering challenges globally.
• Lime stabilization is a common method, forming pozzolanic products like calcite and calcium-silicate-hydrate (C-S-H).
• Traditional engineering tests offer indirect evidence of stabilization effectiveness.

Purpose of the Study:

• To directly quantify pozzolanic products in lime-treated expansive clay soils.
• To validate the efficacy of X-ray Diffraction (XRD) and Differential Thermogravimetric Analysis (DTA) for assessing lime stabilization.
• To correlate mineralogical changes with engineering property improvements.

Main Methods:

• Selection of expansive clay soils with plasticity indices > 25%.
• Application of lime treatment to soil samples.
• Analysis using X-ray Diffraction (XRD) for mineral identification and quantification.
• Differential Thermogravimetric Analysis (DTA) to identify calcium-silicate-hydrate (C-S-H).

Main Results:

• Engineering tests showed significant improvements in strength and reductions in plasticity index (PI).
• XRD analysis revealed a decrease in alumino-silicate minerals (kaolinite, smectite) and the formation of new crystalline phases.
• DTA confirmed the presence of C-S-H, indicated by characteristic weight loss between 140°C and 250°C.

Conclusions:

• XRD and DTA provide direct, quantitative evidence of pozzolanic reactions in lime-stabilized soils.
• These advanced techniques offer a more robust assessment of soil stabilization compared to conventional engineering tests.
• The study confirms the formation of C-S-H as a key product responsible for improved soil performance.