Some types of clay minerals by comparison bonding silica and alumina at its constituent molecules [1] 

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... This research study is a part of research of soft clay and expansive clay stabilization with electrokinetic process. The movement of electricity in the clay caused to several phenomena including electrochemistry, electrophoresis, and elektroosmosis. In this study, the author discusses the phenomenon of cation exchange on expansive clays that occur during the electrokinetic process. Exchanger ions in this study is 2+ a calcium ions (Ca ) which is used as a stabilizer. Research carried out on 3 types of soft clay and expansive to get the behavior of cation exchange phenomenon is more valid and complete on clay soil. Electrokinetic process is done by using direct current (DC) with capacity 5 until 10 Volt. Observation of the phenomenon of cation 2+ exchange is done by measuring the concentration of calcium ion (Ca ) and compared to other ion concentration contained in clay for a certain period by using the AAS method (Atomic Absorption Spectrum). The results 2+ showed that an increase in the concentration of Ca ions in the clay during the electrokinetic process. Increased 2+ + + Ca offset by a reduction in other cations, such as sodium (Na ), and pottasium (K ) in the clay. The results could be used as a basic knowledge in developing electrokinetic processes as an alternative to expansive clay stabilization effort. The ability of electrons moving inside a conductor media, including clay that has a very high plasticity, is one of the advantages of electrokinetic that can be developed and used in the stabilization effort expansive clays. The movement of electrons during the electrokinetic process causes an electric field and allow the release of charged ions that are bound on the surface of the clay molecules. The effect of charged ions that dislocated on the surface of clay molecules cause of changes equilibrium of the electrical charge in clay soil. To establish equilibrium electric charge, the molecules of clay are known to have a negative charge [1] attract and bind positively charged ions (cations) which are located around the molecule clay. This study was conducted to observe the phenomenon of cation exchange on clay due electrokinetic process. Clay is a type of soil that is formed from the weathering of rock core. This soil is composed of several types of minerals, dominated by mineral Silica (SiO 2 ) and Alumina (Al 2 O 3 ) and has a grain size smaller than 2 m  [2]. Composition mineral, both of Silica and Alumina of the clay, affect physical properties and mechanical properties of this soil. Comparison of Silica and Alumina in the clay can be a ratio of 1:1 or 2:1. These combination could be forming different types of clay (Fig. 1). The influence of grain size and mineral clay- forming molecules, causing the soil has a very high plasticity properties [1]. Due to the process chemistry, physics and mechanics, clay has a negative charge on the surface of the molecule [3]. To form a greater molecular bond, clay requires a positively charged ions (cations). Cation can be derived from water molecules that have polar properties and also of metal ions. Type and lots of cations that bound to the surface of the clay molecule affects the number of water molecules that can be attracted by clay molecules and also these cation. Lots of water that bound to molecules of cation determine whether the clay is expansive or not. Electrokinetic is the movement of particles or minerals on a conductor medium that is caused by the electrical. The movement of particles or minerals is caused by an electric field that occurs in media conductor. The electric field in the conductor medium formed by the movement of electrons from the negative (anode) to the positive pole (cathode) [4]. In the basic theory,the movement of electricity in clay can cause phenomena like electrochemical, electrophoresis, elektroosmosis, and also the phenomenon of cation exchange. In real terms this study may also indicate the occurrence of these phenomena, among others, the movement of ions during the electrokinetic process [5] (Fig. 2), and phenomenon of cation exchange [6]. The electric field that formed by the movement of electricity in clay, cause changes electrical charge in the clay. To establish a new equilibrium, molecule of clay need cations. The cations can be obtained from water molecules that have a bipolar nature and also the free cations which are located around the clay molecules. Lime (in the form of solutions, Ca (OH) 2 ) which is used as a stabilizer, due to electrokinetic process undergoes a chemical reaction (electrochemical). If - placed in the chamber of negative electrode (cathode), lime will react and produce hydroxyl ions (OH ), and the 2+ calcium ion (Ca ) if placed in the chamber of positive electrode (anode). The chemical reaction of the aqueous solution of lime (Ca (OH) ) during the electrokinetic process is as ...