International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 10 (2018) pp. 7954-7958 © Research India Publications. http://www.ripublication.com 7954 Influencing of Clay and Binder Content on Compression Strength of Soft Soil Stabilized by Geopolymer Based Fly Ash Son Hoang Trinh 1 , Quynh Anh Thi Bui 2 1 Department of Structure and Construction Material, University of Transport Technology, 54 Trieu Khuc, Thanh Xuan, Hanoi, Vietnam. 2 Department of Geotechnical Engineering, University of Transport Technology, 54 Trieu Khuc, Thanh Xuan, Hanoi, Vietnam. Abstract Soil stabilization with binder now is a common method for treating weak soil. In this study, soft soil was mixed with geopolymer based fly ash binder to improve strength and to be environmentally friendly. Clay soil was mixed with sand to change the clay content by 24.8%, 20.4%, 14.3%, 10.2%, 6.1% and combined with fly ash geopolymer binders at the rates of 5%, 10%, 15%, 20%. Geopolymer based fly ash binder include activated alkaline solution (AAS) Na2SiO3/NaOH = 2, AAS/fly ash = 0.5. Compressive strength of soil specimens stabilized by geopolymer depends on several factors such as clay content, and geopolymer binders. The results show that clay and geopolymer binder content play an important role in the development and formation of strength of geopolymer-soil. Keywords: soil stabilization, geopolymer, compressive strength, clay. INTRODUCTION Soil stabilization is a change of one or more properties of the soil to ensure stability during the construction works and service life. There are two basic methods for soil stabilization: mechanical and chemical methods. The mechanical method based on reducing the porosity, increasing the particle size in the soil. Also, chemical methods based on chemical reactions between soil and binders [2], [3]. Many countries around the world have used chemical methods to improve the soil with organic and inorganic binders in the construction of roads, airports, dams...with significant economic - technical efficiency. The main purpose of soil stabilization by binder is to improve adhesion of soil particles prior to change effects of clay on soil properties such as improving permeability, compressive strength and reduce erosion [4]. Certainly, in the soil, clay particles play a very important role in the formation of mechanical properties, specially permeability and compressibility. They bond coarse particles in the soil together. On the other hand, clay is a component that often changes its properties by moisture. Thereby it has a great effect on the strength and durability of soil. The additives or chemical binder to mechanical properties of soil is to fundamentally change water stability of clay [5]. The term "geopolymer" (geopolymer binder) was first introduced to the world in 1978 by French researcher, Joseph Davidovits. Geopolymer is a type of binder obtained by combining inorganic materials rich of alumosilica (Si-Al) such as metakaoline, fly ash, husk ash, blast furnace slag with chemical compounds called “activated alkaline solution” such as NaOH (or KOH) and Na2SiO3 (or K2SiO3) [6], [7]. The reaction is inorganic polymerization process (also called mineral polymerization). The structure of this geopolymer is "poly-sialate" Si-Al-O. Polysialate chain and ring structure consist of three-dimensional tetrahedrons structures of (SiO4) 4- and (AlO4) 5- by sharing oxygen atoms to replace aluminate (aluminum oxide) with difference degree in all directions. Cations may be any alkaline to neutralize the negative ion of (AlO4) 5- to form monomers in the polysialate network [1]: Mn {- (SiO2)z-AlO2}n.wH2O Where: "M" is a cation or alkaline element (positive ion); "n" is the degree of polymerization; "-" indicates the presence of a bond; "z" is the replacement degree for aluminate (1,2,3 or higher, up to 32). Different dgree of aluminate replacement will produce different geopolymer molecular structures. The Si: Al ratio in the polysialate structure determines the properties of the geopolymer binder. The chemical reaction that forms the geopolymer can be summarize the following steps [1], [7]: Dissolve the Si and Al molecules in the alumosilica material by the hydroxide ions in the activated alkaline solution; Repositioning ions in solution to form monomers; Combining the monomers through the polymerization reaction to form the geopolymer structure. Geopolymers can expose good mechanical properties such as low permeability, high compressive strength, high durability can be achieved if combined at certain conditions [7]. EXPERIMENTAL STUDY Sample preparation material  Soil Soil has unconfined compressive strength of 0.04MPa, unit weight 16.68kg/m 3 , moisture 55.2%. The soil was milled before conduct study. The percent finer and chemical composition are presented in Table 1 and Table 2, respectively.