Investigation of the Mineral Dissolution Rate and Strength Development in Stabilized Soils Using Quantitative X-Ray Diffraction

Abstract

The design of chemical stabilization of clay soils typically relies on empirical studies that utilize 28-day strength, measured as unconfined compressive strength (UCS) or California Bearing Ratio (CBR), as the design criterion. At present, it is generally not possible to extrapolate the results of individual studies to other soils, mainly because there is no quantitative understanding of the chemical reactions that cause strength increase over time. Accordingly, the objective of this study was to investigate whether quantitative X-ray diffraction (QXRD) can be used to establish a quantitative relationship between the mineralogical (microscopic) and strength (macroscopic) properties of kaolinite clay stabilized lime, portland cement, and Class C fly ash. The UCS was observed to change linearly with dry unit weight and logarithmically with time up to 300 days of curing. The kaolinite content in the stabilized samples also decreased logarithmically with time, accompanied by a concomitant increase in the amorphous content that represents the formation of calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH). The overall result was that a highly linear relationship was observed between the UCS and the kaolinite/amorphous content as determined by QXRD. This relationship was different for each of the three stabilizers because portland cement and fly ash exhibit additional cementitious reactions in addition to the dissolution of kaolinite to form CSH/CAH. The study indicates that QXRD is a viable method to produce quantitative assessments of soil mineralogy and that it is possible to pursue the development of models that predict strength of chemically stabilized soils as a function of fundamental parameters, including soil mineralogy and dry unit weight.