Reduction of the Shrinkage–Swelling Potential with Polymer Nanocomposite Stabilization W. R. Azzam Department of Structural Engineering, Faculty of Engineering, Tanta University, Tanta, Egypt Received 25 March 2010; accepted 29 October 2010 DOI 10.1002/app.33642 Published online 27 July 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: This article describes the application of using polymer stabilization to create a new hydrophobic (nanocomposite) material with swollen clay. A series of tests were performed with different polymer contents to study the effect of using polypropylene as a partial soil sta- bilizer and a shrinkage–swelling modifier for expansive soils. The effect of the obtained clay–polymer nanocompo- sites on the shear strength of swelling soils was also investi- gated. The tests showed that the resulting nanocomposites acted as nanofiller materials and decreased both the plastic- ity index and permeability. The optimum moisture content and dry density decreased relatively with increasing poly- mer content. The polymer inclusions significantly reduced the free swelling and swelling pressure values. In addition, the produced nanocomposites reduced the volumetric shrinkage of the expansive soils and created isotropic and compressible materials. The unconfined compressive strength of the soil increased significantly with increasing polymer content. The proposed stabilized technique increased the bearing capacity under the model footing and modified the stress settlement relationship. V C 2011 Wiley Peri- odicals, Inc. J Polym Sci Part A: Polym Chem 123: 299–306, 2012 Key words: additives; adhesion; blending INTRODUCTION For all engineering structures constructed on clayey soils, these soils cause swelling when they are exposed to water and shrink once water is squeezed out. 1 These volumetric changes cause considerable failure to the foundation and damage to the civil infrastructure. 2,3 Expansive soil or swelling clays are mostly found in arid and semiarid regions of the world. In Egypt, swelling clays cover most of greater Cairo, including Nasr City, 6th of October City, and Zayed City. Expansive soils derive their swelling potential mainly from montmorillonite mineral, which is pres- ent in these soils. 4,5 Many chemical investigators 6–8 have dealt with the problem of water adsorption through montmorillonite. The modification of the clay microstructure has been done by with the use of polymers to produce nanocomposite materials with components of clay. Polymers are recognized as one of the most promising research areas in sci- ence and technology in the 21st century. They are used in a wide range of applications to improve and reinforce several material properties. 9 Polymers can be reinforced with different fillers and enhance the mechanical properties of the virgin polymer. Con- ventional fillers, such as talc, mica, CaCO 3 , kaolin, fumed silica, and glass fiber, have been found to increase the mechanical properties with detrimental impacts on the density, transparency, and process- ability. 10 The most common nanosized fillers are car- bon nanotubes, nanosized particles, and intercalated layers. Because nanoparticles have significant surface sizes and quantum effects, their incorporation in a polymer matrix improves several material proper- ties. These improved properties include a high elas- tic modulus, a lower gas permeability, an increased strength, a lower flammability, and increased biodegradability. 11 On the other hand, geotechnical investigations have been carried out to study the swollen clay improvement for foundation uses and to control vol- ume changes. Stabilization by admixtures has been used to prevent volume changes or adequately mod- ify volume changes characteristics of such clays. Lime, cement, pozzolonic flay ash, basalt, and fur- nace slag can be used fairly to stabilize expansive high-plastic clays. 12–17 All of the previous studies have focused on the use of lime flay ash and cement to enhance relatively the geotechnical properties of swollen clay, whereas the application of the use of chemical materials has been limited. In this study, an attempt was made to apply the technique of polymer nanocomposites from the chemical point of view to geotechnical considerations. The use of a polymer to create a new hydrophobic material Correspondence to: W. R. Azzam (azzam_waseim@yahoo. com). Journal of Applied Polymer Science, Vol. 123, 299–306 (2012) V C 2011 Wiley Periodicals, Inc.