10 CHAPTER 2: LITERATURE REVIEW 2.1. General A pavement is a relatively stable crust constructed over the natural soil for the purpose of supporting and distributing wheel loads and for providing an adequate wearing course. These pavements are damaged at a shorter period due to change in the soil properties and due to the repeated application of wheel loads which may result in excessive settlement. Further moisture variation, frost action, Increase (or) decrease of water content in the clay soil causes further deterioration of the pavement which necessitates repair process at a higher cost. The strength of the soil is improved by stabilization. 2.2 Mechanics of Soil Stabilization The term soil stabilization means the improvement of the stability or bearing power of soil by the use of controlled compaction, proportioning and or the addition of suitable admixture or stabilizer. Soil stabilization deals with physical, physico-chemical and chemical methods to make the stabilized soil serve its purpose as pavement component materials. The basic principles in soil stabilization may be stated as follows: • Evaluating the properties of given soil • Deciding the method of supplementing the lacking property by the effective and economical method of stabilization • Designing the stabilized soil mix for desired stability values. • Considering the construction procedure by adequate compaction of stabilized layers. Soil stabilization may result in any one or more of the following changes: • Increase the drain ability of the soil • Increase stability the mineral composition of the materials. any material which is resistance to weathering can be used.3 Mechanical stabilization The Objective of mechanical stabilization is to blend different available soils so that when compacted. 11 • Reduce volume changes • Control the undesirable effects associated with clay. • Improving the local soil This can be achieved by mechanical (or) chemical methods to make the soil stabilized for fulfilling its purpose as pavement component material. . Suitable soil may be selected (contains granular material) and this is to be blended with the available soils to improve the soil properties at a lesser cost in manpower and materials to achieve best results (Increase of CBR). they give the desired stability. The mechanical stability of soil-aggregate mixtures depends upon the mechanical strength of aggregate. Soil type is one of the key features used to determine which method and material should be used for achieving best compaction. In some areas the natural soil at an existing location may have weak in nature (poor CBR). With respect to mineral composition. silt or fine sand. Sodium sulphate and sodium carbonate have a detrimental effect on the stability because of their high volume changes caused by hydration and dehydration. 2. the gradation of the mixture. Presence of chlorides and carbonates are beneficial. the plasticity characteristics of the binder soil and the compaction. • Reduce settlement • Increases sharing resistance • Increases the bearing capacity of soil. It may due to clay. presence of salts. Limitation of mechanical stabilization: • Original soils contains fines.4 Chemical stabilization These are chemical substances that can enter in the natural reactions of the soil and control the moisture getting to the clay particles. therefore converting the clay fraction to permanent cement that holds the mass of aggregate together. mica etc and compaction. • Creation of dust clouds results in nuisance to traffic • Reduction of soil cohesion (or) binding forces ultimately leads to material disintegration. gradation. 12 Factors affecting mechanical stability: The stability of mechanical stabilized soil mixes depends on the following factors: Mechanical strength of aggregates. resulting in a soil mass with higher density and permanent structural change (Raul velas quez et al. it should be susceptible to frost action. The chemical stabilizer in order to perform well must provide strong and soluble cations that can exchange with the weaker clay cations to remove the water from the clay lattice. use of coarser fractions for blending may be expensive • If clay has been added to “Stabilize” soils. properties of soil. 2. 2005) It uses the following • Cement • Lime • Fly ash • Bituminous materials • Other stabilizing chemical admixtures . • More mixing time is required when lime is used and it makes the process uneconomical. chemicals are mixed with soil. creating a film of water around the clay particle that remains attached or adsorbed on the clay . Also surface chemical factors.1 About bio-enzyme Bio-enzyme is a natural. 2. which is difficult to mix thoroughly.5. For other types of chemical stabilization. The presence of Magnesium sulphate reacts with hydrated cement and cause reduction in strength. non-flammable.5. • In the case of lime stabilization. it creates a dust (Hydrated lime) and this is not suitable for thickly populated areas. Enzymes catalyze the reactions between the clay and the organic cat-ions and accelerate the cat-ionic exchange process to reduce adsorbed layer thickness. non-corrosive liquid enzyme formulation fermented from vegetable extracts that improves the engineering qualities of soil. but Bio-enzyme is easy to use as it can be mixed with water at optimum moisture content and then it is sprayed over soil and compacted. Less water results in adequate compaction and more water makes compaction ineffective. non-toxic. facilitates higher soil compaction densities. and increases stability. 13 Limitation of chemical stabilization: • In the case of cement stabilization increase in cement content causes increase in strength and durability [Higher cost].5 Bio-enzymatic Soil Stabilization 2.2 Mechanism of soil stabilization by bio-enzyme In clay water mixture positively charged ions (cat-ions) are present around the clay particles. organic matter and sulphate content alter the properties and durability of soil-cement. Water is a critical component in compaction. 2. Lime requires certain quantum of water for slacking process and it poses a problem in compaction. the search for new materials and improved techniques to process the local materials has received an increased impetus. Cat-ion exchange processes can accomplish this. a suitable stabilization technique has to be adopted for a particular situation after considering the soil properties.3 Bio-enzyme as soil stabilizer in road construction Cost effective roads are very vital for economical growth in any country. 14 surface.5. This has led to the development of soil stabilization techniques. but it can be reduced by drying. In the present study. When poor quality soil is available at the construction site. Hence. These soilstabilizing enzymes catalyze the reactions between the clay and the organic cat-ions and accelerate the cat-ionic exchange without becoming part of the end product. Since the nature and properties of natural soil vary widely. In some cases the clay can swell and the size of double layer increases. Soil improvement by mechanical or chemical means is widely adopted. 2. By utilizing fermentation processes specific micro-organisms can produce stabilizing enzyme in large quantity. Commonly used materials are fast depleting and this has led to an increase in the cost of construction. The adsorbed water or double layer gives clay particles their plasticity. Recently bio-enzymes have emerged as a new chemical for soil stabilization. one type of bio-enzyme has been used for stabilization of five types of soil with varying index properties. There is an urgent need to identify new materials. improve road construction techniques to expand the road network. both inorganic and organic. a number of chemical additives. Therefore to truly improve the soil properties. Detailed laboratory tests were carried out to ascertain the benefits in terms of reduction in design thickness. have also been used. the best option is to modify the properties of the soil so that it meets the pavement design requirements. Bio- . In order to stabilize soils for improving strength and durability. it is necessary to permanently reduce the thickness of double layer. producing clods of stable soil among the roots of the vegetation. When exposed to the air. which might otherwise take years to occur. thus greatly reducing the double layer thickness. The negative charges on the clay platelets are neutralized through this process and the size of the electrical double layer shrinks. These fermentation. Reactions. 2. Bio-Enzyme is convenient to use. This limits further adsorption of water or the resultant swelling with loss of density. In contrast with metal cations. 15 enzymes are chemical. the microorganisms multiply rapidly and produce large organic molecules. the organic cations have large flat structures that approach the size of small clay particles.5. They produce specific enzymes that catalyze the reactions between the clays and the organic cations. formulated products are non-toxic and environmentally harmless. specific microorganisms can produce stabilizing enzymes in large quantities. The enzyme is regenerated by the reaction and goes on to perform again. Nature Plus manufactures and formulations the Terrazyme Soil Stabilizer Product in this manner. Certain soil micro organisms make use of this chemistry to stabilize their environment. While some soil strength gain will become apparent within days. effective and dramatically improves road quality. can be carried out in weeks. These soil-stabilizing enzymes accelerate the cationic exchange without becoming part of the end product. and liquid concentrated substances which are used to improve the stability of soil sub-grade for pavement structures. organic. field research indicates that strength will continue to . which the enzyme attaches to the clay platelets. These organic cations can blanket the clay particle and effectively neutralize its negative charge in a short distance.4 Enzyme stabilization effects Organic cations generated by the growth of vegetation and micro organisms also have the capability to exchange position with other ions attracted to the clay platelet in the soil. safe. By utilizing fermentation processes. the clay will be released from the clay structure and can evaporate. Higher densities and reduced percentages of voids indicate that realignment of soil particles may have occurred during compacting. Field results indicate that soil treated with Terrazyme can reach 95% Modified Proctor with significantly reduced compaction effort. All of the factors . water. which was initially adsorbed on. 16 increase over a period of several weeks. This impact of the Terrazyme Treatment Process on the soil structure correlates with observed reductions in permeability. The reduction in voids resulting from this realignment would decrease pore water within the treated road layer and inhibit water penetration. thus allowing treated soil particles to achieve closer proximity and higher strength. these factors can promote the formation of a stabilized soil structure of superior density and load bearing strength even in soils lacking a significant plastic fines fraction. Terrazyme soil stabilization products are also designed to improve soil strength by increasing the density of initial compaction and facilitating the removal of pore water. Combined with the impact of Terrazyme on the electrical double layer of clay particles. As the soil is exposed to air and the reaction proceeds. soil density increases and the road bearing structure strengthens. nuclear densitometer readings have indicated densities in excess of 100%. As this occurs. which minimizes the destructive impact of water under conditions of loading. Immediately following usual compacting procedures on road materials treated with Terrazyme. These superior initial densities correlate with lower void percentages in the treated and compacted road layer. Compacting of the soil at the optimum moisture content using proper construction methods and equipment is essential to produce the high density necessary for enzymatic stabilization. clay particles are drawn closer together. compaction of the soil at the optimum moisture content using proper construction methods and equipment is essential to produce the high density necessary for enzymatic stabilization. intimate mixing is required to distribute the enzyme solution throughout the soil. little migration takes place within the pore water. Bio-Enzyme is a low cost additive with long lasting effects. sandy loam. non-toxic bio-degradable liquid concentrate that mixes easily in water for application with standard water spraying equipment. and construction materials are now specified using these standards. Bio-Enzyme manufactured in USA and The Netherlands also increases the unconfined compressive strength (UCS) and California Bearing Ratio of sub-grade soil. By altering the physical and chemical characteristics of soil. programme standards for the selection of materials for road construction have been developed. silty clay. and loam mixed with clay. Bio-Enzyme may be used to increase the Maximum Dry Density (MDD) and Unconfirmed Compressive Strength (UCS) values of a marginal material to achieve specified standards for a base course. fine loam. Because the organic ions are very large. 17 discussed can combine to minimize the destructive impact of soil water on the load bearing structure of the treated layer. In addition. materials treated with BioEnzyme retain higher performance levels and extended life span. to achieve the desired results. Bio-enzyme from Australia is a natural. 2. Therefore. Bio-Enzymes are now being used for projects in private sectors as well as in municipal. Based on laboratory experience and field tests. . plastic and non-plastic clay. state and some federal projects. sandy silt. Close adherence to all aspects of the TerraZyme Treatment Process is important to soil stabilization success. Among the soil materials stabilized by the bio-enzymes in the trials are sandy clay.6 Review of Literature In Brazil. without any required maintenance. These stretches of the road are treated with organic soil stabilizer (Bio enzyme). With the test experiments. gradation and CBR. it was found that CBR of stabilized soil increases exponentially for 4 weeks. The amount of dilution water depends on soil dryness. there is an increased cost-effectiveness and improvement in performance and durability of the road. This is because their cost is lower. soil characteristics. After more than 7 months of usage. road sections treated with soil stabilizer showed the following improvements. Three stretches of the road are selected. the application is simpler and less expensive. and transport is cheaper. measurements are made to determine the difference between the actual field soil moisture content (%) and the optimum moisture content (%) to add water to obtain OMC for maximum compaction. 18 The dosage levels of the bio-enzymes vary from 1 litre to 5 litres for 5 m3 of soil depending on the soil type. The soils are tested for plasticity. In the field. . it was found that Bio-Enzyme is suitable for all soil having clay content more than 5 percent with the exception of pure sandy and slerite soil. Even when modest increments in the road stability occur. the usage costs are much lower than conventional chemical stabilizers. Brazetti and Murphy have conducted a lot of field studies in Brazil. Information on the performance of the treated soil structural layers of the roads comes from periodic measurements in the field with DCP (Dynamic Cone Penetrometer) equipment. thereafter the rate of increase in CBR is reduced but keeps on increasing perpetually. In the countries that are using bio-enzyme stabilizers. Based on previous laboratory test results and field trials in Brazil. • Increased CBR (or) capacity to support traffic loading to more than 15 times that of the soil not treated with soil stabilizer. and product concentration. 0. • Minimized creation of dust • Non destructive test was done using Dynamic cone penetrometer (DCP) and found that CBR increases considerably. The road was unpaved road and it affects badly due to adverse weather conditions. One dimensional odometer test was used to conduct swell consolidation test. • No peeling off material due to erosion (or) abrasion from traffic. The treated specimens were kept for curing in desiccators and tested after the curing period. Hitam and Yousof (1998) of palm oil research institute of Malaysia conducted field studies on improvement of plantation roads. 19 • Preserved the structural integrity of the surface (no permanent deformation or plastic effects) with increased cohesion of the base layer material and consequent increase in CBR. India. • No Accumulation of material at the pavement edge. 1% and 2%) The swelling potential and swelling pressure are measured in the one dimensional consolidation load . Soil Specimens are treated with different dosages of bio enzyme (0. • Absence of corrugation on the surface of the pavement after repeated loading condition.50%.2 km of the road and the sections were then monitored on the surface erosion for two monsoon seasons.25%. The specimens are directly prepared in a consolidation ring using static compaction. Sureka Naagesh and Gangadhara (2011) conducted a number of experiments on an expansive soil treated with a bio enzyme stabilizer the expansive soil obtained from Davangere in Karnataka state. No damage was noticed and the researches have concluded that Terrazyme stabilization can convert the road to all weather roads that has minimum destruction in hot and wet seasons. Terrazyme was treated to 27. Also absence of tire marks. • X-ray diffraction studies indicate that noticeable mineralogical changes did not occur in bio-enzyme treated soil on treatment with bio-Enzyme the intensity of the minerals showed marked reduction up to 80%. Specimens with 29% initial water content exhibited 45% reduction in swell potential with 30 days of curing upon further increasing the curing period to 60 days . 20 cell using swell and load procedure.5cc/5 l. The main objective is to investigate the stabilization mechanism of some of the commercially available enzyme based products to understand their potential value for road construction. . Then the soils are treated with two types of Enzyme with variable dosage 0. 1cc. After the addition of enzyme the shear strength of soil also increases considerably. 1. The resilient modulus represents the stiffness of the material tested. The soil tested for sieve analysis and compaction. The result of the test indicated that soils treated with enzymes shows marginal improvements in resilient modulus. • Scanning electron microscopic studies indicate occurrence of changes in the fabric of bioenzyme treated soil specimens the untreated specimens displayed flocculated structure and bio enzyme treated specimens exhibited dispersed structure. the reduction was to be about 50%. Testing results shows increase in the values of resilient modulus for the soils treated with Enzyme. The scanning electron microscopy (SEM) studies on untreated and bio-enzyme treated specimens were conducted in order to ascertain the reasons for reduction in swelling characteristics. Mihai et al 2005 have done experiments on two types of soils with two enzyme products. The following conclusions are drawn: • The soil specimens treated with bio enzyme exhibit lesser percent swell and swell pressure compared to untreated soil specimens.5 cc. 21 Kyle M. economical and environment friendly technique for the stabilization of fine grain soil. and fine) increased significantly at 4 weeks and 14 weeks over the untreated soil samples. The soil samples were laterite. the variation in properties was observed over a short period only and it was found that in cohesive soils there was no major variation in properties during the early days but the soil showed improved performance progressively. Lacuoture and Gonzalez (1995) conducted a comprehensive study of the TerraZyme soil stabilizer product and its effectiveness on sub-base and sub-grade soils. clay and sand. medium. From the study they found that Terrazyme treatment is very effective. 4 and 14 weeks after compaction. fine) using Terrazyme. These samples were tested for grain size analysis and Atterbergs limit. The results from these tests were compared with untreated samples the CBR values for all 3 Terrazyme treated gradation. The soil was treated with different dosage of enzyme. Tests were performed on samples which were allowed to cure for 1.Rollins (2010) has done experimental investigation on 3 types of soils (coarse medium. The reactions of the soils treated with the enzyme was observed and recorded and compared to the untreated control samples. Sharma (2001) has conducted laboratory studies on use of Bio-Enzyme stabilization of three types of soils namely. clay of high plasticity. (coarse. CBR test were conducted on each soil samples at different curing period under soaked condition. Isaac et al (2003) have done experimental studies in the area of Bioenzymatic soil stabilization in the laboratory for different types of soils from Kerala. It was found that soil shows a marginal improvement in CBR value and substantiates reduction in . clay of low plasticity and silt of low plasticity. The optimum moisture content of the soil was determined from modified compaction test. The strength test such as CBR. He concluded that bio-enzyme stabilization has shown little to very high improvement in physical properties of soil. upon completion of construction the trail looked very good but like the other trail sections it did not hold up over the first winter. Manoj Shukla et al (2003) have been made as extensive study on five types of soils with low clay content to very clay content. 22 saturation moisture after four weeks of stabilization. The pavement design thickness is evaluated for enzyme made soil samples for maximum CBR at optimum dosage and cost comparison chart made with conventional design and bioenzyme design. It was found that Pre-wetting of undisturbed samples this swell potential. Also reports showed that successful stabilization with as little as 2% clay in the aggregate material but best result seem to be achieved with 10 to 15% clay. specific gravity. Odometer free swell test were conducted on undisturbed and re-molded playgorsite expansive soil. Atterbergs limit. The soil shows a marginal improvement in unconfined compressive strength. Roger Bergmann (2006) has studied on soil stabilizers on trail surface and concluded that Bioenzymes requires some clay content in the aggregate material in order to create the reaction that will strengthen the material. The mineralogical composition and fabric of soil was analyzed. . The swelling to re-molded samples were higher than undisturbed samples. direct tensile strength and fatigue strength. UCC with and without the use of bio-enzyme at different curing period. OMC and maximum dry density using modified proctor test. Saad Aiban (2006) studied the compressibility and swelling characteristics of eastern Saudi Arabian expansive soil. These soil samples were tested for engineering properties. Tolleson et al (2003) in their research on “An Evaluation of Strength Change on Sub grade Soil Stabilized with an Enzyme Catalyst Solution Using CBR and SSG Comparisons”. road roughness. The effectiveness of enzyme treatment was evaluated on the basis of statistical measurement of change in CBR strength. Not with standing. 62. It was concluded that the CBR test appear to be a relatively poor indicator of direct soil strength for testing conditions. Effects of terrazyme on increase of CBR was studied Soil mechanics laboratory in National Road Department of Thailand (1996) and they found that after one week. . dust levels on the Terrazyme treated road sections. Their objective was to study the potential applicability of tested enzyme for unpaved road in-situ stabilization. plastic limit. two week. optimum moisture content and maximum dry density of cohesive soil of various zone of Surat City of Gujarat state. soil stiffness and soil modulus. a laboratory bench scale testing program was conducted to evaluate the effectiveness of enzyme treatment on sub grade soil. the test result showed CBR strength gain and to a lesser degree strength gain measured by the means of the SSG equipment resulting from the application of the enzyme solution on most soils tested. A correlation is made between CBR and the soil index properties using linear regression model through excel and SPSS software. 23 Andrew R. 66 and 100+ respectively as compared to 28% of untreated soil. and plasticity index. three week. indicating a promising potential for sub grade stabilization using the enzyme solution. The results were analyzed statistically. investigators also reported reduction in gravel loss. and 14 week periods CBR was found as 37. Patel and Desai (2010) proposed a method for correlating CBR values with the liquid limit. the correlation is made between OMC and Plastic limit. The study conducted in China says that lime is the common material used for stabilization. which illuminates the soils formation. The mineral constituent is one of the main characteristics. The mineral constituent has the critical . Taskiran (2010) used artificial intelligence methods for prediction of CBR. He concluded that the undrained shear strength had better correlation with the CBR. CH and SE. A mineralogical analysis was performed using an X-ray Diffracto Meter. 24 Sridharan and Nagaraj (2005) have made a compaction study with 5 different types of soils. Addo has made Non-Destructive study using spectral pavement analyzer (SPA) at the two pavement sites are located in the city of Surrey in British Colombia (Canada). But it destructs and pollutes environment. Further when lime is used to produce the dust and affect the environment heavily in the construction site. Vipulanandan (2010) has studied laboratory and field compacted soil samples falls in the group CL. He concluded that if the Asphalt is in good condition. Mohamed Ali (2001) as per laboratory test to establish the deformation modulus of sub-graded soil as well as inter relationship between CBR and modulus of elasticity for the structural design of highways in Sudan. the Asphalt thickness estimated from SPA tests implies to an accuracy of less than 6%. He proposed an equation between modulus of elasticity and California Bearing Ratio. He concluded that both ANN and GEP are found to be able to learn the relation between the CBR and basic soil properties and can be used for the predicting CBR values of soils. maximum dry density and plastic limit. Artificial neural network and Gene expression programming were applied for the prediction of CBR of fine grain soils from Southeast Anatolia region Turkey. studies on x-diffraction. 25 effect to the soil’s characteristic. Different types of soil stabilization techniques have been used (Mechanical. Shankar et al (2009) have done experimental work on lateritic soil collected from Dakshina Kannada and Udupi districts. The clay which belongs to secondary mineral is the most activist mineral constituent. The soil which was collected from Thong chuan in Shanxi was treated with Terrazyme. and scanning election microscope shows the increase of strength after adding Terrazyme. The expansive soil is treated with semi processed lime with an application rate of 10% by weight further the expansive sub grade was treated with a combination of hydrated lime and a Terrazyme. UCC values the soil treated with Enzyme shows a marginal improvement. A comparative study on different trial sections reveals that Terrazyme stabilization gives fruitful results. Again these soils are tested for Engineering properties. By comparing CBR. . So. CBR and UCC over different curing periods. The expansive sub grade is mechanically stabilized by mixing it with non – plastic gravel with a proportion of 50% by volume and compacted to the required density. The measurement of CBR. Then these soils are treated with different dosages of Enzyme. Tewodros Alene (2010) has done Extensive study in Ethiopia on expansive soils. the clay is mainly solidified when the soil is solidified. Nine trial sections were formed by using different materials. The construction of test sections is carried out on a road with Expansive sub grade along the Chancho Ginchi road. The lateritic soil and blended lateritic soil are tested for Engineering properties. lime and chemical stabilization). CBR and UCC. 8 • Minimized creation of dust. 2. • Improves structural integrity and load capacity. • Improves the soil structure sufficiently which results in cost savings up to 25%.7 General findings based on literature review • Most researchers found that the application of Terrazyme on the soil improves the CBR to a large extent. 4. resulting in fewer maintenance needs. 2. To develop suitable specifications and recommendations for evolving proportions for its use in subsurface layers. • Improves CBR. and reduces the occurrence of serious defects such as pot holes ad rut formation. 26 2. • Suitable for road to all weather seasons. • Application of Terrazyme offer good result on an expansive soil. To validate mathematical model with experimental results . UCC. and Shear strength of soil • Decrease of plasticity index Objectives of the Present research work The objectives of the present research work are: 1. 3. To optimize the quantity of Bioenzyme to be used as stabilizing agent and the extent of stabilization of strength gain with time. To study the effect of Bioenzyme on the quality of sub grade/base course layers and its influence on pavement system.
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