Surface area characteristics of expansive clays – for sustainable infrastructure development
Mentor:Binod Tiwari, Associate Professor , California State University Fullerton
Clays are considered to be the most problematic soils for the foundation of any civil engineering structures. Therefore, research on the behavior of clays upon the application of foundation soil is important. An important property of clay when considering modification, commonly done by adding admixtures such as cement and lime, is the Cation Exchange Capacity (CEC). The CEC of clay is a measurement of the maximum amount of Cations that are available for exchange in the clay. This physicochemical property is an indicator of how to properly modify clay. Measuring the CEC is a very important step as there is currently no universal test method to measure the CEC accurately. The effectiveness of the tests used differs depending on the types of clays and minerals present in the soil. Therefore, developing relationships between the results for these tests and the actual CEC is very important. The Specific Surface Area (SSA) is directly related to the CEC and measuring one is an indirect measure of the other. More than 20 clay mineral mixtures were prepared in the lab and the specific surface area of those mixtures were measured with two different methods – N2BET Method (measurement done based on the absorbing capacity of Nitrogen Gas) and Methylene Blue Concentration Method (titration of the soil with Methylene Blue). The first method is very expensive but more accurate than the second one, and the second method is cheaper than the first one and could be established by many geotechnical engineering labs at less expense. Results of this research show a strong relationship between two methods of measurement for SSA. The output of this research is a mathematical correlation between specific surface area calculated by two different methods and also a regression equation between methylene blue concentration, specific surface area and CEC of soil.