A Systematic Literature Review on Performance of Fly Ash On the Strength Parameters in Cohesive Soils

Transcription

1 A Systematic Literature Review on Performance of Fly Ash On the Strength Parameters in Cohesive Soils Mohamadreza Mahmoudi 1, Hamed Niroumand 2, Khairul Anuar Kassim 3 1 Master student, Department of civil engineering, Faculty of engineering, Islamic Azad University, Central Tehran Branch, Iran 2 Post-Doctorate, Assistant Professor, Department of geotechnical engineering, Faculty of civil engineering, Buein Zahra Technical University, Iran 3 PhD, Professor, Department of geotechnical engineering, Faculty of civil engineering, Universiti Teknologi Malaysia, Malaysia ABSTRACT Fly ash, generated during the combustion of coal for energy production, is an industrial by-product which is recognized as an environmental pollutant. Fly ash utilization program must be extensively taken up covering various aspects at different level to minimize the environmental pollution. Fly ash is generally grey in color, abrasive, mostly alkaline, and refractory in nature. Fly ash is often placed in class F fly Ash and class C fly ash. The geotechnical properties of fly ash such as specific gravity, permeability, internal angular friction, and consolidation characteristics make it suitable for use in construction of roads and embankments, structural fill and especially on clay soils. The purposes of this article are divided to geotechnical assessment of recycled and waste materials and performance evaluation of fly ash on the strength parameters of cohesive soils that the mineralogical analysis can be established by X-ray diffraction (XRD) analysis or scanning electron microscopy (SEM). In this regard the major soil strength test performed is compaction, California Bearing Ratio, Unconfined Compression Strength and Triaxial tests. A systematic literature review has been written on performance of fly ash on the strength parameters of cohesive soils. KEYWORDS: Fly ash, waste material, strength parameters, cohesive soil INTRODUCTION Every year large amounts of coal are burned in coal-fired power plants. This poses a serious problem in terms of create a landfill for it and potential environmental pollution. Fly ash is defined as the material extracted from the flue gases of a furnace fired with coal. Fly ash consists of often hollow spheres of silicon, aluminum, and iron oxides and unoxidized carbon. Furthermore, the properties of fly ash depend on the type of coal and method used for the power generation in the power plants. Expansive soil swell and shrink with change in water content and loose strength upon inclusion of water. Clayey soils usually have the undesirable engineering behavior, such as low bearing capacity, high shrinkage and swell characteristics and high moisture susceptibility. montmorillonite is the most common of all the clay minerals in expansive clay soils. montmorillonite minerals exhibit high shrinkage and swelling characteristics. Many

2 Vol. 19 [2014], Bund. Z additives such as lime, cement, fly ash, bitumen, Calcium Chloride, Sodium Chloride are being used for stabilization of these soils. Stabilization of expansive soils with admixtures controls the potential of soils for a change in volume, and improves the strength of soils. The use of fly ash as an additive results in less shrinkage in comparison with soft soils treated with lime or cement alone. Fly ash when mixed with expansive clays the cation exchange, presence of free lime, and pozzolanic reaction provide the required effect to control the swelling and improve the strength of expansive clays. High-lime (Class C) fly ashes with any other activators is more economical alternatives for a wide range of stabilization applications. Addition of fly ash reduced compressibility characteristics of expansive clays. Settlement of structures built on improved soils with fly ash decreases and the time required for reaching the final settlement is reduced. Fly ash can be used in soil to get improvement in shear strength, cohesion and improvement in the bearing capacity. Fly ash method also reduced plasticity and free swell characteristics. Furthermore, it binds the soil particles together that leading to an increase in CBR values of the improved soils. In addition, fly ash has advantageous properties such as low specific gravity, lower compressibility, high volume stability, and pozzolanic reactivity. Using an industrial byproduct such as fly ash as an additive to civil engineering construction materials prevents its serious effects on environment. Table 1 illustrated the various researches on performance of fly ash in cohesive soils. Edil et al. [1] evaluated the effectiveness of self-cementing fly ashes for stabilization of soft fine-grained soils. California bearing ratio (CBR) and resilient modulus (MM rr ) tests were conducted on mixtures. Different soft fine grained soils such as inorganic soils and organic soil and different fly ashes were used. Two of the fly ashes are high quality Class C ashes and the other ashes are off-specification ashes. Tests were conducted on soils and soil fly ash mixtures prepared at optimum water content and different wet of optimum water content. The results showed that addition of fly ash significantly, increased the CBR and MM rr of the inorganic soils. On the other hand, CBR of soil fly ash mixtures generally increased with fly ash content and decreased with increasing compaction water content. Furthermore, fly ash should be stiffen over time to increase the resistance of the pavement. Organic soil typically had much lower CBR and MM rr values from inorganic soils. However, for wetter or more plastic fine grained soils the resilient modulus had further increase. Cokca [2] used from high-calcium and low-calcium class C fly ashes for stabilization of an expansive soil and evaluation of the expansive soil-lime, expansive soil-cement, and expansive soil-fly ash systems. Lime, cement and fly ash were added to the expansive soil at different percentages. The specimens were subjected to chemical composition, grain size distribution, consistency limits, and free swell tests. Also, the Specimens with fly ash were cured and after that they were subjected to oedometer free swell tests. It can be concluded that the expansive soil can be successfully stabilized by fly ashes. Furthermore, plasticity index, activity, and swelling potential of the samples decreased with increasing percentage of stabilizer and curing time. Prasad and Sharma [3] evaluated the effectiveness of clayey soil blended with sand and fly ash for soil stabilization by studying the subgrade characteristics. The purpose of this work is to find a solution for proper disposal of fly ash and also provides good subgrade material for pavement construction. The results showed that substantial improvement in compaction and California bearing ratio of composite containing clay, sand and fly ash. The swelling of the clay also reduced after stabilization. The maximum dry density of clay-sand-fly ash mix decreased with the addition of fly ash and optimum moisture content increased. Thus the stabilized soil can be used for construction of flexible pavements in low traffic areas. Bose [4] used fly ash to stabilize a highly plastic clay. The geo-engineering properties such as, atterberg limits, grain size distribution, linear shrinkage, free swell index, welling pressure,

3 Vol. 19 [2014], Bund. Z compaction characteristics, unconfined compressive strength and CBR value of virgin clay and stabilize with fly ash were evaluated. Expansive soil was stabilized with various proportion of fly ash. The results showed that plasticity index of clay-fly ash mixes decreased with increase in fly ash content. Thus addition of fly ash increases its workability by colloidal reaction and changing its grain size. The free swell index value and swelling pressure of expansive clay mixed with fly ash decreased with increase in fly ash content. Furthermore, addition of fly ash reduced the optimum moisture content but the dry density increased and unconfined compressive strength of clay-fly ash mixes is found to be maximum. So, it is concluded that the fly ash has a good potential for improving the engineering properties of expansive soil. Kumar and Sharma [5] presented a study of the efficacy of fly ash in improving the engineering characteristics of expansive soils. An experimental program evaluated the effect of the fly ash on the free swell index, swell potential, swelling pressure, plasticity, compaction, strength, and hydraulic conductivity characteristics of expansive soil. The results showed that the plasticity, hydraulic conductivity and swelling properties of the blends decreased and the dry unit weight and strength increased with an increase in fly ash content. The resistance to penetration of the mixtures increased significantly with an increase in fly ash content for a certain water content. Excellent correlation was obtained between the measured and predicted undrained shear strengths and the undrained cohesion (cc uu ) of the expansive soil blended with fly ash increased with the fly ash content. Kate [6] explored the possibility of utilizing the fly ash with or without lime for stabilizing the expansive soils to improve strength and volume change behavior. The free swell index, swell, swelling pressure and unconfined compressive strength tests have been conducted on expansive soils with mixing bentonite with kaoline clay in different proportions. The results showed that the swelling characteristics such as free swell index, maximum swell and swelling pressure decreased with increase in percentage of fly ash. These values are decreased considerably by addition of small percentage of lime to fly ash. Negligible changes in Unconfined Compressive Strength values have been observed with increase in percentage of fly ash. Whereas, the addition of lime increases these values significantly. These soils that stabilized with fly ash alone did not show marked change in immediate strength. However, curing caused a remarkable increase in their strengths. As a final result, the soils with low expansivity can be stabilized with appropriate percentage of fly ash alone. However, for medium to high expansivity shoud be used from small percentage of lime and fly ash. Kumar Pal and Ghosh [7] presented the consolidation and swelling characteristics of fly ash and montmorillonite clay blends. Different types of fly ash with different percentage of montmorillonite clay were added to each samples. Specimens were compacted at the optimum moisture content and the maximum dry density. In this regard, the standard Proctor compaction tests were used. Furthermore, the effect of permeability, free swell index and plasticity of fly ash montmorillonite clay mixtures were evaluated. The results showed that immediate settlement of fly ash takes place in a short period of time during consolidation, and secondary settlement is negligible. There was not any significant change in vertical compression of fly ash samples. The compression index (cc cc ) of the fly ashes and montmorillonite clay repectively, showed fast consolidation and endurance large deformation of mixtures. So, in soft soils, fly ash can be used to reduce embankment settlement. Phanikumar and Sharma [8] studied the effect of fly ash on the volume change of a highly plastic expansive clay and a nonexpansive clay with low plasticity. The effect of fly ash on free swell index, swell potential, and swelling pressure of expansive clays were evaluated. Moreover, Compression index and secondary consolidation characteristics of both clays were also determined. The results showed that Swell potential and swelling pressure, when determined at

4 Vol. 19 [2014], Bund. Z constant dry unit weight of the mixture, decreased and when determined at constant weight of clay, increased. Compression index and coefficient of secondary consolidation of both the clays decreased by addition fly ash. So, the settlement of structures built on this stabilized clays decreased and consolidation happened in shorter time. Furthermore, maximum dry unit weight increased and optimum moisture content decreased with increasing fly ash content. Lopes et al. [9] examined the applicability of fly and bottom ash on the layers of pavements by mixing these ashes with a non-lateritic sandy-silty soil, with and without lime addiction. This study, presented the results of physical and chemistry characterization, and compression, resilient modulus and permanent deformation, after environmental testing solubilization and leaching. The results showed that the soil is dependent on confining pressure and the inclusion of fly ash and the mixture cure and these parameters increase the value of resilient modulus. On the other hand, the addiction of bottom ashes increased immediately the resilient modulus of the mixtures. The mixtures with or without the addition of lime, with the presence of bottom and fly ash, had mechanical behavior compatible with the requirements of pavement with low traffic volume. Lin et al. [10] studied two expansive soils from a microscopic point to better understand the cation exchange capacity, mineralogical, and microstructural changes that occur during Class C Fly Ash stabilization. X-ray diffraction (XRD) was used to monitor the mineralogical changes and scanning electron microscopy (SEM) was adopted to observe the microstructural alterations. Energy Dispersive X-ray Spectroscopy (EDXS) was used to evaluate the distribution of the stabilization agent inside the specimen. It was found that the CFA stabilization process reduced the plasticity index (PI), clay size fraction, percent of swell, swell pressure, and volumetric water contents of the soil water characteristic curves, and increased the unconfined compressive strength. The reaction between soil and fly ash caused the iron-oxide coating that verified by both XRD and energy-dispersive X-ray spectroscopy analysis. The combined effects of flocculation and coating reduced the water-retention property of the stabilized soils, decreased their swell potential, and increased the soil strength. Vizcarra et al. [11] presented the characteristics of municipal solid waste (MSW) incineration ash and evaluates this ash in road pavement layers through the mixture of ash with a clay soil. Chemical, physical, and mechanical tests and the mechanistic-empirical design for a pavement structure were carried out on the pure soil and also in the soil mixture with the addition of different ash content. The results showed that fly ash reduced the expansion of the material, showing an increase in the California bearing ratio (CBR) and resilient modulus value. Furthermore, content and type of ash was important in final results and it showed the efficacy of MSW fly ash for its use in base road pavement layers. Mir and Sridharan [12] studied adding, high calcium and low calcium fly ashes in different proportions to a highly expansive black cotton soil. The objective of the study was to study the effect of fly ashes on the physical, compaction, and swelling potential of black cotton soils that were reached from laboratory tests and utilization of waste material without disruptive effect on the environment. The results showed that the liquid limits, compaction characteristics and swelling potential of expansive soil fly ash mixtures are significantly modified and improved. With the addition of fly ash to black cotton soil the maximum dry unit weight of the mixtures decreases with increase in optimum moisture content and it can be attributed to the improvement in gradation of the fly ash. Furthermore, compressibility characteristics of the expansive soil are improved with the addition of fly ash. Misra et al. [13] studied the laboratory evaluation of the stabilization characteristics of clay soils blended with self-cementing class C fly ash and residual self-cementation of ponded class C fly ash. The stabilization characteristics were evaluated with reaching to the uniaxial compressive

5 Vol. 19 [2014], Bund. Z strength stiffness, and swelling potential. So, twelve set of mixtures of clay soils with the percentages of kaolinite and montmorillonite, self-cementing fly ash and appropriate amount of water were compacted and cured. For swelling test, the cured samples were inundated and with using the one dimensional oedometer apparatus. Furthermore, unconfined compression and CBR tests were used. The results showed that the optimum moisture content changes due to the addition of fly ash. The samples rapidly gained compressive strength and stiffness within seven days curing period, and the greatest increase occurred in one day due to the rapid hydration reaction of fly ash. With increasing in montmorillonite content, strength of the samples increased significantly. By increasing in fly ash content, swelling potential of stabilized clay may be reduced. CBR values showed that the ponded class C fly ash can be a good substitute as a base course material. Zha et al. [14] presented laboratory tests to evaluate the effect of adding fly ash and fly ashlime on the geotechnical behavior of the expansive soil in terms of grain size distribution, atterberg limits, specific gravity, compaction characteristics, free swell, swell potential, swelling pressure, axial shrinkage percent, and unconfined compressive strength. In this regard, the influence of curing time on the swell potential, swelling pressure, and unconfined compressive strength was investigated. The relationship between the plasticity index and swell-shrinkage properties for soils was discussed. The results showed that the plasticity index, activity, free swell, swell potential, swelling pressure, and axial shrinkage percent decreased with an increase in fly ash or fly ash-lime content. With the increase of the curing time for the treated soil, the swell potential and swelling pressure decreased. There was not significant change in the unconfined compressive strength. However, after curing of the samples, the unconfined compressive strength increased significantly. Furthermore, with an increase in fly ash and limefly ash content, the optimum water content and the maximum dry unit weight decreased. Nalbantoglu [15] used Cation Exchange Capacity values to indicate the changes in the mineralogy of the fly ash-soils mixtures and explain the reduction in the plasticity and water absorption potential. Cation Exchange Capacity values were used to explain the effect of the pozzolanic reaction on the particle size and the swell potential of the treated soils. The results indicated that fly ash is effective in improving the structure and plasticity of the fly ash-soil mixture by reducing the content of clay size particles, plasticity index and the swell potential. However, the reduced Cation Exchange Capacity values indicated that fly ash improvement changes in the mineralogy of the improved soils and produced the new minerals. These pozzolanic reaction is caused the soils to become more granular and less water absorption potential. Prabakar et al. [16] investigated the behavior of soils mixed with fly ash to improve the load bearing capacity of the soil. Three different types of soil and different percentage of fly ash were used. The objectives of this investigation was reached to the usefulness of fly ash-soil mixtures, and focused to improve the engineering properties of soil with better load bearing capacity. This study also mentioned the cost effective of fly ash for soil improvement and covered the compaction behavior, settlement, California bearing ratio, shear strength parameters and swelling characteristics. The results showed that addition of fly ash reduced the dry density of the soil and unit weight of soil. The void ratios and porosity changed with increasing content of fly ash in soils. The shear strength of the mixture was improved due to the addition of fly ash and increasing of it was nonlinearly. The value of cohesion increased by the addition of fly ash and this alteration was linear. CBR value of soil improved by the addition of fly ash. The results indicated that the shear strength and the angle of internal friction of soil admixed with fly ash caused a better strength. Using fly ash in soil also reduced swelling in the soil. Even, the fly ash

6 Vol. 19 [2014], Bund. Z improved the shear strength, cohesion and bearing capacity. So, this mixture can be used as the base materials for the roads, back filling and etc. Temimi et al. [17] studied the addition of fly ash in the clay soils. Different clay-fly ash samples were tested by means of oedometer tests in order to find the effect of fly ash on the mechanical properties of clay materials. It indicated that the inclusion of fly ash in the clay material improved the mechanical properties of the clay, like the compressibility and the consolidation. So, compressibility and the settlement, decreased and the consolidation of clay increased. Senol et al. [18] presented using of self-cementing fly ashes without any other activators for the stabilization of four different types of soft subgrades. The samples were prepared by mixing fly ash at different contents at changeable water contents. The laboratory tests such as index properties, compaction, unconfined compressive strength and CBR tests were used. To developing water content strength relationship, samples were subjected to unconfined compression strength and California bearing ratio tests after seven days curing time. To evaluating the impact of compaction delay, the samples were compacted two hours later after mixing with water. The results showed that the fly ash increased both the unconfined compressive strength, and the CBR values and can replace with soft subgrade of highways. So, stabilizing the soft subgrade at specified water contents and minimizing compaction delay could maximize the strength of mixtures. Bin-Shafique et al. [19] conducted an experimental study to investigate the long-term performance of fly ash to improve two fine-grained soil subbases and focused on the effect of weathering action, such as wet dry cycles and freeze thaw cycles on the performance of this mixture. Specimens were from low plasticity clay and high plasticity expansive soil that improved with a Class C fly ash. The samples were subjected to twelve cycles of wet dry and freeze thaw, in a controlled laboratory condition with change in geotechnical properties of the weathered blends to understand the long-term performance. Wet dry cycles conducted with tap water and saline water. Furthermore, plasticity index tests, unconfined compression tests, and vertical swell tests were used. The fly ash increased the unconfined compressive strength of finegrained soil significantly and decreased the plasticity and swell potential. Freeze thaw cycles reduced stabilized samples strength but after this reduction, the strength was still higher than the strength of unstabilized samples. Wet dry cycles with saline water reduced the plasticity but did not have any effect on strength. A slight decrease of the vertical swelling was also observed after wet dry cycles using saline water. The freeze thaw cycles did not change the plasticity of the stabilized soils but decreased the unconfined compressive strength of stabilized expansive soils. Also, vertical swelling increased rapidly and then increased very slowly. Mirsa [20] examined clay stabilization with Class C fly ash. Physical and chemical properties of fly ash and compaction and strength behavior of soils stabilized with Class C fly ash were discussed. Examples were prepared by blending a small proportion of bentonite with kaolinite. Furthermore, fly ash had a rapid hydration characteristic. So, higher densities and strengths were achieved when the compaction is performed with little or no delay. However, delayed compaction produces low densities and strength. It was observed that the stabilization characteristics are related to the soil mineral type and plasticity. The laboratory studies indicated that use of Class C fly ash in soil stabilization was dependent on the ash contents, water content, compaction delay, strength development with time and curing methodology and the type of clay mineral. Thus, these Class C fly ashes are particularly suited for use as soil improvement agents. Sivapullaiah et al. [21] presented the effect of fly ash and lime, on the index properties of expansive soils such as liquid limits, plastic limits and free swell. The studied soil was black

7 Vol. 19 [2014], Bund. Z cotton soil. The results showed that the index properties of this soil were significantly varied by addition fly ash. It is observed that the domain of alteration depends on the particle size distribution, free lime content and pozzolanic reactivity of the fly ash. The effect of the coarseness of fly ash particles is to decrease the activity. Thus, fly ash can decrease the plasticity index of the soil. The effect of the addition of fly ash is to significantly improve the physical properties and workability of the black cotton soil. Parsons and Kneebone [22] quantified the level of improvement provided by Class C fly ash and determined of the mixture deterioration with fly ash during the time. A series of dynamic cone penetrometer values were obtained for treated or untreated subgrades with fly ash. Pavements ranged in age from zero to nine years. Laboratory tests also showed that fly ash contributed to soil strength and stiffness while plasticity and swell potential were reduced. Use of fly ash alone for stabilization may not be sufficient to improve soil properties to desired levels. In addition, an improved subgrade assisted to the strength of the pavement, and may provide reductions in costs and the thickness of the asphalt section. Sezer et al. [23] presented an investigation into the stabilization of a soft clay subgrade with a very high lime fly ash. The objective of this paper was to use very high lime fly ash in soil stabilization without using any other activator and to investigate some strength characteristics of fly-ash clay mixtures. Different percentages of the soil was replaced with fly ash. In addition, for different stabilized soil samples with fly ash at optimum water contents, standard proctor test was conducted. The tests lasted for 3 months and the unconfined compressive strength and shear strength parameters, cohesion and internal friction angle, were determined. It was found that, inclusion of fly ash improved the properties of the soil. The maximum dry density decreased and optimum moisture content increased with increasing fly-ash content. In addition, the fly ash increased the unconfined compressive strength and cohesion of the soil. Amu et al. [24] studied the stabilizing of an expansive clay soil with the combination of cement and fly ash. The samples were classified to three groups; cement optimal mix, cement plus fly ash optimal mix and unstabilized sample. The three different classes of sample were subjected to Maximum Dry Densities, Optimum Moisture content, California Bearing Ratio (CBR), Unconfined Compression and Undrained Triaxial test. The results showed that the soil sample stabilized with a mixture of cement and fly ash had better performance with attention to maximum dry densities, optimum moisture content, bearing capacity and shearing resistance tests. Furthermore, the addition of certain percentage of fly ash improved the stabilizing potential of cement on an expansive clay soil. Sharma et al. [25] reported the improvement in the strength of a cohesive soil by addition of both fly ash and lime. In this regard, X-ray diffraction, scanning electron microscopy, coupled with energy dispersive spectroscopy (EDS), thermal gravimetric analysis, zeta potential and ph value test was carried out in order to explain the stabilization mechanism. On the other hands, an experimental program was conducted to evaluate the effect of the fly ash content on the free swell index, plasticity, compaction characteristics, unconfined compressive strength, California bearing ratio and Atterberg limits of a cohesive soil. In addition, dosages of fly ash and lime were determined to yield optimum strength of soil. The XRD, SEM, EDS, and zeta potential confirmed the breaking of montmorrillonite structure in the untreated clay after stabilization. It was also confirmed that the pozzolanic reaction dominated over the cation exchange capacity. The results showed that the strength increases of soil happened with addition both of fly ash and lime. In addition to, from PH value test a minimum lime content was recommended for stabilizing the soil. The unconfined compressive strength and CBR value increased by addition of fly ash and lime. The addition of fly ash also improved the geotechnical properties of the soil.

8 Vol. 19 [2014], Bund. Z Buhler and Cerato [26] used lime and Class C fly ash to reduce the plasticity of highly expansive clays. Soil samples with similar classification were used to show shrinkage variability with the addition of lime and Class C fly ash. The plasticity reduction was determined with linear shrinkage test. The results showed that both lime and fly ash reduced the linear shrinkage but the addition of lime caused further decrease in linear shrinkage. The high unit weight of fly ash relative to lime has made its lag in shrinkage reduction. So, we needed less lime than fly ash to reduce the plasticity of a highly expansive soil whereas fly ash is a waste product of power plant and it is more cost effective than lime. Puppala et al. [27] used from fly ash and fiber reinforcement methods, to treat and increase the strength of two expansive soils. In this regard Physical tests such as Atterberg limits, standard Proctor compaction and other tests like unconfined compressive strength, shrinkage, and free swell were conducted on both raw and treated clay samples. Both methods showed an increase in unconfined compression strength of the soils. Improvement with fly ash decreased free swell, plasticity and linear shrinkage strains of raw soils. Fiber reinforcement decreased the vertical shrinkage strains. Whereas, it increased the free swell values. In general, the fly ash treatment method can be used to stabilize expansive soils, and fibers can be used to increase the strength and decrease the shrinkage potentials of expansive soils. In addition, the important point is that fibers alone will not provide comprehensive stabilization. Another advantage of the two methods was that both stabilizers were recycled waste products and therefore their use in soil stabilization will reduce landfilling costs. Senol [28] performed an experimental study to investigate the effects of fiber on the compaction and strength behavior of high plasticity clay with fly ash in different proportions. The soil samples were prepared with different percentages of fiber content and fly ash. Different tests such as optimum moisture content, unconfined compression strength, compaction and Atterberg limits test were conducted. The results showed that fibers acted like a reinforcement in the soil and prevented the formation of cracks whereas fly ash bound the soil particles together that is caused to an increase in CBR values of the stabilized soil. The inclusion of fiber caused an increase in the CBR, increase the strength of the fly ash specimens and changed their brittle behavior into ductile behavior. Further increase was observed in strength when both fiber and fly ash were used. So, the combination of fiber and fly ash is an efficient method to ground improvement. Brooks et al. [29] studied an experimental program to evaluate the potential of limestone dust and coal fly ash to stabilize some problem soils. The tests such as Atterberg limits, compaction, California bearing ratio (CBR), swell, and unconfined compressive strength were used. A oneway analysis of variance test performed on the generated data. Results showed that the plasticity and swell of the soils were reduced. A significant increase was observed in strength of the soils for CBR and UCS when stabilized with the additives. Maximum dry density of the soil-additive mixture decreased and optimum moisture content of the mixture increased with increase in additive content. Division [30] studied the effect of geo-textile as a reinforcement in the subgrade by conducting cyclic plate load tests. The soil was mixed with optimum of fly ash and optimum of CCCCCCCC 2 for the construction with or without reinforcement. Compaction properties and CBR values were determined for the soil and it categorized as high plasticity clay. The results showed that the utilization of fly ash and fly ash - CCCCCCCC 2 as an admixture significantly increases the load carrying capacity of the sub grade soil and also a significant increase in load carrying capacity of the stabilized soil was happened by providing composite geo-textile as reinforcement at Optimum moisture content condition.

9 Vol. 19 [2014], Bund. Z Athanasopoulou [31] evaluated the improvement in engineering properties of clayey subgrade that was stabilized with lime or fly ash. In this regard, California bearing ratio (CBR) tests were used to evaluate the bearing strength of stabilized soils. The results showed that admixture of lime or fly ash caused an increase in the plasticity limit, while the liquid limit and the plasticity index of the soils have been reduced. However, further increases in the California bearing ratio value obtained when the soil samples were mixed with lime. Also, the swelling reduced with the addition of both additive materials. The increase in optimum moisture content increased CBR value, particularly at high lime or fly ash percentages. Furthermore, the maximum dry density reduced with addition of lime and fly ash. Kumar et al. [32] studied the effects of polyester fiber inclusions and lime stabilization on the geotechnical characteristics of fly ash-soil mixtures. The geotechnical characteristics of fly ashsoil specimens, lime-soil specimens and lime-fly ash-soil specimens mixed with different proportions of randomly oriented fibers were investigated. Test specimens were subjected to compaction tests, unconfined compression tests and split tensile strength tests. Specimens were cured after which they were tested for unconfined compression tests and split tensile tests. The results showed that with the increase in lime content, the maximum dry density of soil-lime mixes decreases and optimum moisture content increases but fly ash decreases further maximum dry density and optimum moisture content increases. However polyester fibers had no significant effect on maximum dry density and optimum moisture content. With the increase in the percentage of fly ash while the lime is constant, strength tends to increase and reaches a certain maximum value and after that it starts decreasing. The ratio of split tensile strength and unconfined compressive strength increases with increase in fiber content. So, polyester fibers are more efficient when soil was subjected to tension rather than to compression. Furthermore a good stabilization can be formed on expansive soils by the combination of fibers, lime, and fly ash. Table 1: A systematic literature review on performance of fly ash in cohesive soils Author(s) Year Subject Results Sivapullaiah et al Mirsa 1998 Effect of fly ash on the index properties of black cotton soil. Stabilization Characteristics of Clay Using Class C Fly Ash. The influence of fly ash is related to particle size distribution, free lime content and pozzolanic reactivity of it. The effect of the coarseness of fly ash particles is to decrease the activity and plasticity index of the soil. Use of Class C fly ash in soil stabilization was dependent on the ash contents, water content, compaction delay, strength development with time and curing methodology and the type of clay mineral. Also, the stabilization characteristics are related to the soil mineral type and plasticity.

10 Vol. 19 [2014], Bund. Z Temimi et al Erdal Cokca Puppala et al Prabakar et al Nalbantoglu 2004 Phani Kumar & Sharma 2004 Amu et al Recycling of fly ash in the consolidation of clay Soils. Use of class C fly ash for the stabilization of an expansive soil. Fiber and fly ash stabilization methods to treat soft expansive soils. Influence of fly ash on strength behavior of typical soils. Effectiveness of Class C fly ash as an expansive soil stabilizer. Effect of fly ash on engineering properties of expansive Soils. Stabilizing potential of cement and fly ash mixture expansive clay soil. Inclusion of fly ash in the clay material improves the mechanical properties of the clay, like the compressibility and the consolidation. Plasticity index, activity, and swelling potential of the samples decreased with increasing percentage of fly ash and curing time. So, the expansive soil can be successfully stabilized by fly ashes. The fly ash treatment method can be used to stabilize expansive soils, and fibers can be used to increase the strength and decrease the shrinkage potentials of expansive soils and fibers alone will not provide comprehensive stabilization. Both methods showed an increase in unconfined compression strength of the soils. Both stabilizers were recycled waste products and therefore their use in soil stabilization will reduce landfilling costs. The fly ash improves the shear strength, cohesion and bearing capacity. So, this mixture can be used as the base materials for the roads, back filling and etc. Fly ash is effective in improving the structure and plasticity of the fly ash-soil mixture by reducing the content of clay size particles, plasticity index and the swell potential. Fly ash improvement changes in the mineralogy of the improved soils and produces the new minerals and it is caused the soils to become more granular and less water absorption potential. With addition of fly ash plasticity, hydraulic conductivity and swelling properties decreased and the dry unit weight, strength and undrained cohesion (cc uu ) of mixture increased with an increase in fly ash content. With attention to maximum dry densities, optimum moisture content, bearing capacity and shearing resistance tests the soil sample stabilized with a mixture of cement and fly ash had better performance. Furthermore, the

11 Vol. 19 [2014], Bund. Z Parsons & Kneebone 2005 Misra et al Kate 2005 Field performance of fly ash stabilized subgrades Physico-mechanical behavior of selfcementing class C fly ash clay mixtures Strength and volume change behavior of expansive soils treated with fly ash. Edil et al Stabilizing soft finegrained soils with fly ash. Senol et al Sezer et al Soft subgrades stabilization by using various fly ashes. Utilization of a very high lime fly ash for improvement of Izmir clay. addition of certain percentage of fly ash improved the stabilizing potential of cement on an expansive clay soil. Fly ash contributed to soil strength and stiffness while plasticity and swell potential were reduced. Also, use of fly ash alone for stabilization may not be sufficient to improve soil properties to desired levels. The clay-fly ash samples rapidly gained compressive strength and stiffness within curing period. By increasing in fly ash content, swelling potential of stabilized clay ma reduces and CBR values improves. Swelling characteristics such as free swell index, maximum swell and swelling pressure decreased with increase in percentage of fly ash. Whereas, the addition of lime increases these values significantly. Furthermore, curing process caused a remarkable increase in strength of fly ash mixtures. Addition of fly ash significantly, increased the CBR and resilient modulus of the inorganic soils. Fly ash should be stiffen over time to increase the resistance of the pavement. The fly ash increases unconfined compressive strength, and the CBR values and can replace with soft subgrade of highways. Inclusion of fly ash improved the properties of the soil. The maximum dry density decreased and optimum moisture content increased with increasing fly-ash content. In addition, the fly ash increased the unconfined compressive strength and cohesion of the soil.

12 Vol. 19 [2014], Bund. Z Kumar et al Buhler & Cerato 2007 Phanikumar & Sharma 2007 Zha et al Influence of fly ash, lime, and Polyester fibers on compaction and strength properties of expansive soil Stabilization of Oklahoma expansive soils using lime and class C fly ash. Volume change behavior of fly ash stabilized clays. Behavior of expansive soils stabilized with fly ash. With the increase in lime content, the maximum dry density of soil-lime mixes decreases and optimum moisture content increases but fly ash decreases further maximum dry density and optimum moisture content increases. However polyester fibers had no significant effect on maximum dry density and optimum moisture content. With the increase in the percentage of fly ash while the lime is constant, strength tends to increase and reaches a certain maximum value and after that it starts decreasing. The ratio of split tensile strength and unconfined compressive strength increases with increase in fiber content. So, polyester fibers are more efficient when soil was subjected to tension rather than to compression. Both lime and fly ash reduced the linear shrinkage but the addition of lime caused further decrease in linear shrinkage because of high unit weight of fly ash relative to lime. So, we need less lime than fly ash to reduce the plasticity of a highly expansive soil whereas fly ash is a waste product and it is more cost effective than lime. Settlement and swell potential of structures built on this stabilized clays with fly ash decreased and consolidation happened in shorter time. Furthermore, maximum dry unit weight increased and optimum moisture content decreased with increasing fly ash content. The plasticity index, activity, free swell, swell potential, swelling pressure, and axial shrinkage percent decreased with an increase in fly ash or fly ash-lime content. With the increase of the curing time for the treated soil, the swell potential and swelling pressure decreased further. With an increase in fly ash and lime-fly ash content, the optimum water content and the maximum dry unit weight decreased.

13 Vol. 19 [2014], Bund. Z Bin-Shafique et al The long-term performance of two fly ash stabilized fine grained soil subbases. Geotech Division 2011 The efficacy of reinforcement technique on the fly ash stabilized expansive soil as a subgrade embankment for highways. Brooks et al Bose 2012 Lopes et al Sharma et al Geotechnical properties of problem soils stabilized with fly ash and limestone dust in Philadelphia. Geo engineering properties of expansive soil stabilized with fly ash. Appicability of coal ashes to be used for Stabilized pavements base. Stabilization of a Clayey Soil with Fly Ash and Lime: A Micro Level Investigation The fly ash increased the unconfined compressive strength of fine-grained soil significantly and decreased the plasticity and swell potential. The freeze thaw cycles did not change the plasticity of the stabilized soils but decreased the unconfined compressive strength of stabilized expansive soils. Wet dry cycles with saline water reduced the plasticity but did not have any effect on strength. The utilization of fly ash and fly ash - CCCCCCCC 2 as an admixture significantly increases the load carrying capacity of the soil and also a significant increase in load carrying capacity of the stabilized soil was happened by providing composite geo-textile as reinforcement at Optimum moisture content condition. The plasticity and swell of the soils were reduced. A significant increase was observed in strength of the soils for CBR and UCS when stabilized with limestone dust and coal fly ash. Maximum dry density of the soiladditive mixture decreased and optimum moisture content of the mixture increased with increase in additive content. Plasticity index, free swell index value and swelling pressure of clay-fly ash mixes decreased with increase in fly ash content. Addition of fly ash reduced the optimum moisture content but the dry density increased and unconfined compressive strength of is found to be maximum. In addition, addition of fly ash increases its workability by colloidal reaction and changing its grain size. Addition of bottom ashes increased immediately the resilient modulus of the mixtures and presence of bottom and fly ash had mechanical behavior compatible with the pavement. Addition of fly ash and lime increases strength of soil. The unconfined compressive strength and CBR value increased by addition of fly ash and lime. Addition of fly ash also improved the geotechnical properties of the soil.

14 Vol. 19 [2014], Bund. Z Senol 2012 Lin et al Sridharan Calderon Vizcarra et al. Athanasopoulou Kumar Pal & Ghosh Prasad & Sharma Effect of fly ash and polypropylene fibres content on the soft soils. Effect of fly ash on the behavior of expansive Soils: microscopic analysis. Physical and Compaction Behavior of Clay Soil-Fly Ash Mixtures. Applicability of municipal solid waste incineration ash on base layers of pavements. Addition of Lime and Fly Ash to Improve Highway Subgrade Soils 2014 Volume change behavior of fly ash montmorillonite clay mixtures Influence of sand and fly ash on clayey soil stabilization. Fibers acted like a reinforcement in the soil and prevented the formation of cracks whereas fly ash bound the soil particles together that is caused to an increase in CBR values. The inclusion of fiber caused an increase in the CBR, increase the strength of the fly ash specimens and changed their brittle behavior into ductile behavior. Stabilization with class C fly ash reduce the plasticity index, clay size fraction, percent of swell, swell pressure, and volumetric water contents of the soil water characteristic curves, and increase the unconfined compressive strength. The liquid limits, compaction characteristics and swelling potential of expansive clay soil fly ash mixtures are significantly improved. Furthermore, compressibility characteristics of the expansive soil are improved with the addition of fly ash. Fly ash reduced the expansion of the material, showing an increase in the California bearing ratio (CBR) and resilient modulus value. Furthermore, content and type of ash was important in final results. Admixture of lime or fly ash caused an increase in the plasticity limit, while the liquid limit, swelling and the plasticity index of the soils have been reduced. Further increases in the California bearing ratio value obtained when the soil samples were mixed with lime. The increase in optimum moisture content increased CBR value, particularly at high lime or fly ash percentages. Furthermore, the maximum dry density reduced with addition of lime and fly ash. In soft soils, fly ash can be used to reduce embankment settlement. The swelling of the clay reduced after stabilization with fly ash. The maximum dry density of clay-sand-fly ash mix decreased with the addition of fly ash and optimum

15 Vol. 19 [2014], Bund. Z moisture content increased. Substantial improvement happened in compaction process and California bearing ratio of composite containing clay, sand and fly ash. CONCLUSION The generation of fly ash is more than its utilization. It can be used as an alternative material instead of conventional materials in the construction of geotechnical and infrastructures. If desired results are found in future studies on fly ash in soil stabilization, we could see large reductions in material costs. On the other hands, fly ash is a good material for use in geotechnical applications. The low unit weight of fly ash makes it acceptable for placement in soft soils. Addition of fly ash altered the physical and compaction characteristics of both granular and cohesive soils. Fly ash can create an adequate array of cations than under ionized conditions it can improve flocculation of dispersed clay particles. According to a cation exchange process, the influence of fly ash on expansive soils causes significant reduction of plasticity index, activity, and swell potential. In addition, pozzolanic reaction of it results in formation of cemented combinations with high shear strength and low volume change. The combination of soil and fly ash improves liquid limit, plastic limit, and CBR values to acceptable limits. Fly ash increases strength and decreases shrinkage strains of expansive soils. It can be concluded that fly ash treatment method can be used to stabilize expansive soils. In this regards, there are some recommendation for future that listed as follows: The mechanism making the off-specification fly ash effective in stabilizing organic soils needs further study. Fly ash use as a stabilizer for expansive soils has not been investigated to a significant bound. Whereas, there is still a need to find new uses of this material and in this case that it will use less fly ash. For the actual practice, further laboratory studies are needed to understand long-term behavior of expansive clays treated with fly ash and effect of alternate drying and wetting on shrinking, swelling, swelling pressure and strength characteristics of improved expansive clays. Extensive researches are needed to understand the mechanisms and geotechnical properties of swelling soils stabilized with fly ash because the two problems of swelling and shrinkage of these soils will make a lot of damage to the structure. More research is needed to provide a deeper understanding of the microscopic mechanisms occurring in the Class C Fly Ash stabilization process and their relationship with mechanical soil characteristics. Understanding this connection is crucial for future numerical modeling of the mechanical behavior of stabilized expansive soils. further study may be required by ensuring the uniform distribution of fly ash into the soil to achievement the linear curves. Further experimental investigations should be conducted on other treated expansive soils to estimate the performance accuracy of plasticity index ratio method in the prediction of the swell-shrinkage properties.