Application of Advances in Materials Chemistry and Mineralogy in Soil Stabilization

Advances in the state-of-the-art of physicochemical stabilization of geomaterials have preceded deep understanding of the fundamental processes that underlie projects that have been implemented. Before the past 2 decades or so, experiments with a variety of chemical substances with soils of diverse mineralogy have produced results that have generally been adequate for matching chemical additives with soils of known mineralogical composition and grain size characteristics. Often, empirical measures of soil material volumetric instability, such as shrink/swell potential and plasticity indices, were used along with some basic understanding of soil mineralogy, to estimate the required quantity and frequency of application of soil stabilization agents. During the past 2 decades, advances in analytical techniques coupled with increased use of wastes and recycled products in soil stabilization, have enabled the expansion of the science and technology of soil stabilization.

Recent innovations in soil stabilization with respect to the development of more effective agents, matching of climatic and soil mineralogical factors with the chemistry of agents, understanding of the transport and toxicological characteristics of stabilization agents, and advancements in damage modeling of stabilized soils have arrived at an opportuned time. The expansion of physical infrastructure such as roads, pipelines, airports, and housing, etc. into reclaimed and marginal lands to serve growing populations in many countries has generated the need for refinement of soil stabilization techniques to improve cost-effectiveness and also requires application of more rational models that can be adapted to a diversity of materials in many climatic and geohydrological environments when estimates of stabilized material durability and life-cycle maintenance costs are to be made. An interesting example of the utility of technical advances in soil stabilization is the use of chelating agents to bind metals to roadside soils. In this sense, physicochemical stabilization is used as a contaminated media remediation technique. Considering that in many regions of the world, dusts and water-eroded sediments are transferred in huge quantities from unpaved roadways, mining sites, farmlands, and waste piles into sensitive ecological environments, innovations have taken the utility of soil stabilization beyond control of strength and stability of earthworks under variable moisture content, temperature fluctuations, and load, to the control of contaminant emissions.

Although trade names mask the chemistry of specific chemical stabilizing agents that are presently in commerce, they are generally salts, emulsified asphalt products, petroleum products, polymeric liquids, lignins, water, and clay additives. Some of the agents such as petroleum products are binding agents while others, such as aqueous polymers and water, reduce soil surface friability. Additives such fly ash and paper sludges also serve various stabilization functions in soils. Undoubtedly, stabilizing material chemistry and soil mineralogy play significant roles with respect to the thermodynamics and kinetics of stabilization reactions in a given geochemical environment. Although thermodynamics as a field has limitations in this realm because of uncertainties in material composition at microscale reaction sites, it is still possible to use these fundamental analyses to gain insight into the patterns of physicochemical interactions that determine the effectiveness of stabilization processes.