Soil Stabilization Using Lime and Fly Ash

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ABSTRACT Soil is the basic foundation for any civil engineering structures.It is required to bear the loads without failure.In some places, soil may be weak which cannot resist the oncoming loads.In such cases,soil stabilization is needeed.Numerous methods are available in the literature for soil stabilization.But sometimes,some of the methods like chemical stabilization,lime stabilization etc. adversly affects the chemical composition of the soil. In this study,fly ash and lime were mixed with clay soil to investigate the relative strength gain in terms of unconfined compression,bearing capacity and compaction.The effect of fly ash and lime on the geotechnical characteristics of clay-fly ash and clay-lime mixtures was investigated by conductiung standard Proctor compaction tests,unconfined compression tests,CBR tests and permeability test.The tests were performed as per Indian Standard specifications. The following materials were used for preparing the samples: Clayey soil Fly ash Lime The soft clay used for these experiments was brought from a site,near Kumarakom.The physical properties of the soil were determined as per IS specifications. Fly ash for the study was brought from Hindustan Newsprints,Piravam.it is finely divided residue resulting from the combustion of ground or powdered coal from electric generating plants. It has high water absorption capacity. Lime for the study is locally available.it imparts much strength to the soil by pozzolanic reaction which is explained later in the report.

In this test programme,without additives clay was tested to find the optimum moisture content ,CBR value ,plasticity index and unconfined compression strength.Fly ash and lime were added in varying percentages and that fraction for which maximum strength is obtained was found out.The mixture is cured for 3,7 and 14 days.

CHAPTER 1 INTRODUCTION General

Transport in the Republic of India is an important part of the nation's economy. Roads are the vital lifelines of the economy making possible trade and commerce. They are the most preferred modes of transportation and considered as one of the cost effective modes. An efficient and well-established network of roads is desired for promoting trade and commerce in any country and also fulfills the needs of a sound transportation system for sustained economic development. To provide mobility and accessibility, all weather roads should connect every nook and corner of the country. To sustain both static and dynamic load, the pavement should be designed and constructed with utmost care. The performance of the pavement depends on the quality of materials used in road construction. Sub grade is the in situ material upon which the pavement structure is placed. Although there is a tendency to look at pavement performance in terms of pavement structures and mix design alone, the subgrade soils can often be the overriding factor in pavement performance. The construction cost of the pavements will be considerably decreased if locally available low cost materials are used for construction of lower layer of pavements such as subgrade, sub base etc.If the stability of local soils is not adequate for supporting the loads, suitable methods to enhance the properties of soil need to be adopted. Soil stabilization is one such method. Stabilizing the subgrade with an appropriate chemical stabilizer (such as

Quicklime, Portland cement, Fly Ash orComposites) increases subgrade stiffness and reduces expansion tendencies, it performs as a foundation (able to support and distribute loads under saturated conditions). This report contains a summary of the performance of lime and fly ash used with clay.

Fly ashes are finely divided residue resulting from the combustion of ground or powdered coal from electric generating plants. Lime is another additive used, which is locally available, to improve subgrade characteristics. It is obtained by heating limestone at elevated temperatures. SCOPE OF THE PROJECT The soil used in the study is natural clay brought from Kumarakom.Pavement subgrade over there is composed of clayey soil whose bearing capacity is extremely low.Due to this reason ,the roads require periodic maintenance to take up repeated application of wheel loads.This proves to be costly ,and at the same time, conditions of raods during monsoon seasons is extremely poor.Therefore, a thought on how to enhance the stability of roads by chaper means demands appraisal. Soil stabilization can be done using different additives ,but use of fly ash which is a waste material from thermal power plants,at the same time difficult-to-dispose material will be much significant.

OBJECTIVES OF THE PROJECT The major objectives of the project are:1.

To explore the possibility of using flyash in road construction programme. clayey soil.

2. To study the effect of lime and flyash on proctors density and OMC of

3. To study the effect of lime and flyash on the consistency limits of clayey soil.4.

To study the changes in CBR of soil by the addition of lime and fly ash

5. To study the effect of curing period on the properties of clayey soil.

CHAPTER 2 LITERATURE REVIEW General Stabilization is the process ofblending and mixing materials with a soil to improve certain properties of the soil. The process may include the blending of soils to achieve adesired gradation or the mixing of commerciallyavailable

additives that may alter the gradation, texture or plasticity, or act as a binder for cementationof the soil. The process of reducing plasticity and improving the texture of a soil is called soil modification. Monovalent cations such as sodium and potassium are commonly found in expansive clay soil and these cations can be exchanged with cations of higher valenciessuch as calcium which are found in lime and flyash. This ion exchange process takes place almost rapidly, within a few hours. The calcium cations replace the sodium cations around the clay particles, decreasing the size of bound water layer, and enable the clay particle to flocculate. The flocculation creates a reduction in plasticity, an increase in shear strength of clayey soil and improvement in texture from a cohesive material to a more granular, sand-like soil. The change in the structure causes a decrease in the moisture sensitivity and increase the workability and constructability of soil. Soil stabilization includes the effects from modification with a significant additional strength.

Soil structure The clay particles in the soil structure are arranged in sheet like structures composed of silica tetrahedral and alumina octahedra. The sheets form many different combinations, but there are three main types of formations .the first is kaolinite,which consists of alternating silica and alumina sheets bonded together. This form of clay structure is very stable and does not swell appreciably when wetted .the next form is montmorillonite, which is composed of two layers of silica and one alumina sheet creating aweak bond between the layers. This weak bonding

between the layers allows water and other cations to enter between the layers,resulting in swelling in the clay particle. The last type is illite, which is very similar to montmorillonite ,but has potassium ions between each layer which help bond the layers together. Inter layer bonding illite is therefore stronger than for montmorillonite,but weaker than kaolinite. Clay particles are small in size but have alarge to mass ratio,resulting in alarger surface area available for interaction with water and cations.the clay particles have negatively charged surfaces that attract cations and polar molecules,including water forming a boundwater layer around the negatively charged clay particles. The amount of water surrounding the clay particles is related to the amount of water that is available for the clay particle to take in and release. This moisture change around the clay particles causes expansion and swelling pressures within clays that are confined .

Uses of stabilization Pavement design isbased on the premise that minimum specifiedstructural quality will be achieved for each layerof material in the pavement system. Each layermust resist shearing, avoid excessive deflectionsthat cause fatigue cracking within the layer or inoverlying layers, and prevent excessive permanentdeformation through densification. As the qualityof a soil layer is increased, the ability of that layerto distribute the load over a greater area isgenerally increased so that a reduction in therequired thickness of the soil and surface layersmay be permitted.

Quality improvement. The most common improvementsachieved through stabilization includebetter soil gradation, reduction of plasticity indexor swelling potential, and increases in durabilityand strength. In wet weather, stabilizationmay also be used to provide a working platformfor construction operations. These types of soilquality improvement are referred to as soil modification. Thickness reduction. The strength and stiffnessof a soil layer can be improved through theuse of additives to permit a reduction in designthickness of the stabilized material compared withan unstabilized or unbound material.

STABILIZATION TECHNIQUES Stabitization with portland cement Portland cement can be used either to modify or improve the quality of the soil into a cemented mass with increased strength and durability. The amount of cement used will depend upon whether the soil is to be modified or stabilized. Cement stabilization is most commonly used for stabilizing silt, sandy soils with small quantities of silt or clayey fractions stabilization of soil with cement has been extensively used in road construction. Mixing the pulverized soil and compact the mix to attain a strong material does this stabilization. The material thus obtained by

mixing soil and cement is known as soil cement. The soil content becomes a hard and durable structural material as the cement hydrates and develops strength. The cementing action is believed to be the result of chemical reaction of cement with the siliceous soil during hydration. Stabilization with bitumen Stabilization of soils and aggregates with asphalt differs greatly from cementand lime stabilization. The basic mechanism involved in asphalt stabilization of fine grained soils is a water proofing phenomenon. Soil particles soil agglomerates are coated with asphalt that prevents or slows the penetration of water, which could normally result in a decrease in soil strength. In addition, asphalt stabilization can improve durability characteristics by making the soil resistant to the detrimental effects of water such as volume. In non-cohesive material such as sand and gravel, crushed gravel, and crushed stone, two basic mechanisms are active: water proofing and adhesion. The asphalt coating on the cohesion less materials provides a membrane, which prevents or hinders the penetration of water and thereby reduces the tendency of the material to lose strength in the presence of water. The second mechanism has been identified as adhesion. The aggregate particle adheres to the asphalt and the asphalt acts as a binder or cement. The cementing effect thus increases the shear strength by increasing adhesion. Criteria for design of bituminous stabilized soils and aggregates are based almost entirely on stability and gradation requirements. Freeze-thaw and wet durability test are not applicable for asphalt-stabilized mixtures. Stbilization with lime-cement and lime-bitumen

The advantages in using combination stabilizers are that one of the stabilizers in the combination compensates for the lack of effectiveness of the other in treating a particular aspect or characteristics of a given soil. For instance in clay areas devoid of base material, lime have been used jointly with other stabilizers notably Portland cement or asphalt, to provide acceptable base courses. Since Portland cement or asphalt cannot be mixed successively with plastic clays, the lime is incorporated into the soil to make it friable, thereby permitting the cement or asphalt to be adequately mixed. While such stabilization might be more costly than the conventional single stabilizer methods, it may still prove to be economical in areas where base aggregate costs are high. Two combination stabilizers are considered in this section. 1. lime-cement 2. lime-asphalt Lime-cement Lime can be used as an initial additive with Portland cement or the primary stabilizer. The main purpose of lime is to improve workability characteristics mainly by reducing the plasticity of soil. The design approach is to add enough lime to improve workability and to reduce the plasticity index to acceptable levels. The design lime content is the minimum that achieves desired results. Lime-asphalt Lime can be used as an initial additive with asphalt as the primary stabilizer. The main purpose of lime is to improve workability characteristics and to act as an antistripping agent. In the latter capacity, the lime acts to neutralize acidic chemicals in

the soil or aggregate, which tend to interfere with bonding of the asphalt. Generally, about 1-2 percent lime is all that is needed for this objective. Stabilazation by geo-textiles and fabrics Introducing geo-textiles and fabrics that are made of synthetic materials, such as polyethylene, polyester, and nylon, can stabilize the soil. The geo-textile sheets are manufactured in different thickness ranging from 10 to 300 mils (1mil=0.254mm). The width of sheet can be upto 10m. These are available in rolls of length upto about 600m. Geotextiles are permeable. Their permeability is compared to that of fine sand to course sand and they are strong and durable.

STABILIZATION WITH LIME Lime stabilization is done by adding lime to soil. This is useful for the stabilization of clayey soil. When lime reacts with soil there is exchange of cations in the adsorbed water layer and a decrease in the plasticity of the soil occurs. The resultant material is more friable than the orginal clay, and is more suitable as subgrade. Lime is produced by burning of limestone in kiln. The quality of lime obtained depends on the parent material and the production process. And there are basically 5 types of limes 1. High calcium, quick lime (CaO)2.

Hydrated high calcium lime [Ca(OH)2]

3. Dolomitic lime [CaO+MgO]

4. 5.

Normal, hydrated Dolomitic lime [Ca(OH)2+MgO] Pressure, hydrated dolomitic lime[Ca(OH)2+MgO2]

The two primary types of lime used in construction today are quick lime(calcium oxide) and hydrated lime (calcium hydroxide).Heating limestone at elevated temperatures produce quick lime and addition of water to quick lime produces hydrated lime. Equation shows the reaction that occurs when limestone is heated to produce quick lime with carbon dioxide produced as by-product. CaCO3+heat CaO+CO2

Addition of water to quick lime produc...