Scienceline Publications Journal of Civil Engineering and Urbanism 2252-0430 6 4 2016 July A Review of Physical and Chemical Clayey 64 71 http://www.ojceu.ir/main/attachments/article/53/J.%20Civil%20Eng.%20Urban.,%206%20(4)%2064-71,%202016.pdf EN Ali Akbar Firoozi Department of Civil and Structural Engineering, Universiti Kebangsaan Malaysia (UKM), Selangor, Bangi,43650, Malaysia Ali Asghar Firoozi Department of Civil and Structural Engineering, Universiti Kebangsaan Malaysia (UKM), Selangor, Bangi,43650, Malaysia Mojtaba Shojaei Baghini Department of Civil and Structural Engineering, Universiti Kebangsaan Malaysia (UKM), Selangor, Bangi,43650, Malaysia Clays in general and expansive soils in particular have been a major concern to geotechnical engineers for many years. Moisture variations produce big volume changes in these types of soils. Several factors like amount and type of clay minerals, soil structure, dry density, confining pressure, moisture content and climate changes influence the amount of swell and shrinkage. These volume changes finally result in serious damage to the various structures including pavements. In addition, clayey soils are usually stiff when they are dry and give up their stiffness as they become saturated. Soft clays (i.e. illite/kaolinite/ montmorillonite) are associated with low compressive strength and excessive settlement. This reduction in strength due to moisture leads to severe damages to buildings and foundations. Clay structure Cation Exchange Capacity Atterberg limits