Stabilization nature and unified strength characterization for cement-based stabilized soils

• Sand/silt fraction usually just acts as hard inclusion in cement-based stabilized soil. • A modified binder/water ratio involving clay/water ratio and binder/water ratio was proposed to characterize UCS. • The linear slope between the UCS and modified ratio reflects cement hydration and pozzolanic reaction with clay mineral. Although extensive studies have been conducted on cement-based stabilized soils (CBS), there is limited research focusing on the effect of water content, sand/silt fraction and particle size distribution of the original clays on the unconfined compression strength (UCS) of CBS. In this study, experimental results were combined with the available data collected from the literatures to clarify the effect of the water content, sand/silt fraction and size distribution on the CBS strength and to develop a generalized predictive strength equation for clays with various gradations, water contents and cement contents. The findings suggest that at a constant cement mass, original dry clay and water, the addition of sand (<80% in this case) has no influence on the UCS. However, at the same cement mass, water, and total soil (e.g., original clay with incorporated sands), the UCS decreases because of less absorbed water and more available water with sand substitution. It can be concluded by the scanning electron microscopy (SEM), that sand acts as hard inclusions within the CBS matrix. Based on the nature of the sand function within the CBS, a modified binder/water ratio (new indicator) was proposed to characterize the UCS by combining the traditional binder/water ratio and the mass ratio of the clay fraction to water. Using the modified binder/water ratio, the strength predictive equation was developed, which is useful as a tool for mix design to attain a target strength. The powerfulness of the equation is confirmed by the prediction results of the available CBS data collected from the literatures. The slope of the equation is found to be dependent on the cement hydration and pozzolanic reaction with clay minerals.