Experimental Investigations on Chemically Treated Sulfate Soils For Fundamental Understanding of Heaving Mechanisms

University Of Texas At Arlington, Arlington TX

Investigators

Abstract

Sulfate-rich cohesive soils are found in several regions of the United States. When the sulfate-rich soils are treated with calcium based lime and cement stabilizers for soil improvements, the sulfates in soils react with the calcium of stabilizers and alumina of clayey soils to form a crystalline mineral, ettringite. This mineral, upon hydration, undergoes a large amount of heave in the soils. This heave is termed as sulfate induced heave in the literature. Buildings, pavements, runways and embankments built on cement and lime treated sulfate-bearing soils have been affected by this heave distress. Repair and maintenance of the distressed structures costs millions of dollars annually. Potential heave problems may arise in the future due to the increased use of industrial sulfuric waste products for soil stabilization and solidification. Hence, it is necessary to fundamentally understand sulfate-stabilizer reaction mechanisms in soils that cause sulfate heave movements. This project is designed to investigate the influence of soil compositional and environmental factors on the heave mechanisms in sulfate rich soils and establish problematic sulfate levels for various soil compositional and environmental variables. Four types of clayey soils with different types of clay mineralogies, two cement and lime treatment levels, five sulfate amounts, two moisture content levels, and three temperature conditions will be investigated. Treated and untreated soil samples will be prepared, cured if necessary, by accelerated curing methods at different temperatures and then tested under a variety of mineralogical, chemical and engineering swell, suction potential and shear strength tests. Test results will be analyzed to understand the possible causes of sulfate heave mechanisms and investigate time periods at which ettringite formation takes place in soils. Additionally, models will be developed to predict problematic sulfate levels in soils at which heave distress can be expected for a given chemical treatment. These models will be verified by comparing their predictions with the known heave distresses of field sites. This project will make a strong contribution to the fundamental understanding of the sulfate induced heaving mechanisms in soils. Potential benefits of this research project are: (1) develop problematic sulfate conditions for different clayey soils at which cement and lime treatments cause heave distress, (2) develop better chemical treatment methods in the future by targeting the factors that influence the ettringite formation, and (3) facilitate the use of sulfuric wastes for recycling applications in stabilization. Also, applications of free alumina and electric conductivity measurements in soils to identify problematic sulfates will be evaluated. This project will also have a strong impact on the researchers' educational activities. An integral part of this project is to teach swell, shrink, mineralogical and chemical characterization methods as well as data acquisition, data reduction and analysis and data presentation concepts to graduate and undergraduate students. Both graduate and undergraduate students will be encouraged to work as a team in performing the research tasks. The research project information will be made available to interested individuals through the web address of the geotechnical program. Updates on research status and findings will be posted throughout the year. Also, the research findings will be disseminated in various journals and proceedings articles.