Applicability of the Porosity/Binder Index to Nonhomogeneous Mixtures of Fine-Grained Soil with Lignite Fly Ash

Soil treatment using binders is an important method to enhance the strength, stiffness, and durability of soils. The porosity/binder concept has been developed to help with the mixture design for soil stabilization measures and has been verified for homogeneous mixtures. Unfortunately, in cases in which the base soil is fine-grained, it is typically not possible to obtain perfect mixture homogeneity on site. In such cases the binder typically forms a crust around soil clods. This study examines the applicability of the porosity/binder index to such non-homogeneous mixtures. For this purpose, the unconfined compressive strength of samples produced from homogeneous and non-homogeneous mixtures have been compared. In these mixtures, the addition rate, the dry density, and the water content were varied. It was found that the porosity/binder concept can be used to predict the strength of non-homogeneous field gradations of stabilized soils, provided that the clod size and water content of the laboratory samples resemble the clod size and water content of the material on site. The precision of predictability decreases with increasing variations of water content and mixture homogeneity.