An Experimental Investigation On Stabilizing The Soil Using Rice Husk Ash With Lime As Admixture

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1 Research Paper Volume 3 Issue 9 May 2016 International Journal of Informative & Futuristic Research ISSN: An Experimental Investigation On Stabilizing The Soil Using Rice Husk Ash With Lime As Admixture Paper ID IJIFR/V3/ E9/ 068 Page No Subject Area KeyWords Civil Engineering Black Cotton Soil, RHA, Lime, OMC, California Bearing Ratio, Unconfined Compressive Strength 1 st R. Oviya 2 nd R.Manikandan M.E. Student Soil Mechanics and Foundation Engineering Karur College of Engineering, Karur-Tamilnadu (India) Assistant Professor Department of Civil Engineering Karur College of Engineering, Karur-Tamilnadu (India) Abstract In India, one-fifth of our land area is covered by black cotton soil which is also known as expansive soil. These soils are mostly found in arid and semi-arid regions. These soils are found to be highly problematic in constructional activities. It causes severe damages to the structure because of its alternate swelling and shrinkage nature. This happens due to alternate drying and wetting of soil. To avoid these circumstances, soil must be stabilized and strength is to be increased. Soil can be modified or improved by many methods which include mechanical methods, use of chemicals or wastes as stabilizing agent etc. From the above said methods, improvement to soil by using waste material is beneficial and effective one. In our country, wastes are generated from various ways. It includes domestic wastes, industrial wasters, agricultural wastes etc. It is very difficult to dispose these wastes without affecting the environment and its surroundings. To overcome these problems, it can be used as a stabilizing agent in the soil. By using the wastes as stabilizing agent, it not only increases the strength of soil but also paves way in reducing the construction cost, easy way for waste disposal and turns the environment to be eco-friendly. This paper presents about an experimental study carried out to find the effect of Rice Husk Ash (RHA) which is an Published On: 31 ST May, 2016 Available online through

2 agricultural waste on index and engineering properties of the expansive soil. The properties such as compaction, California bearing ratio, unconfined compressive strength is determined with partial replacement of RHA in black cotton soil at various percentages(2.5%, 5% etc) in addition of lime in small amount to it at a constant rate of 2%. On the results achieved, it gives a conclusion that the Optimum moisture content (OMC) increases with the addition of RHA in soil. The California Bearing ratio is also having a tremendous increase in strength with soil mixed with RHA and the optimum percentage of RHA with soil is found to be 5% and RHA with lime and soil is found to be 10% effectively. Thus a promising and improving result is obtained in stabilizing the soil with Rice Husk Ash in both cost and strength evaluation. 1. INTRODUCTION 1.1 Black Cotton Soil Expansive soil which is also called as black cotton soil is very difficult to be used in construction. This is due to hot climate and poor drainage conditions associated with these soil formations. These soils inhibit the moisture from the surface in monsoon and summer season by means of evaporation. Owing to these reasons, the soil possess cyclic swell-shrink behavior, low strength, high moisture content, volume change in soil, differential settlement etc. These failures may result in longitudinal and transverse cracking of pavements, surface distress, rutting of surface and deep cutting in foundations. To overcome these circumstances in the soil, it should be treated and stabilized in best way. 1.2 Stabilization Stabilization is mostly used in variety of engineering works, where it is main objective is to increase the strength and improve the durability and stability of the soil in a cost effective way. Soil stabilization is the application or treatment of soil by mechanical methods or addition of modifier (cement, lime, bitumen etc.,) or combination of both to improve the strength of the soil. Expansive soil can also be stabilized by using waste materials. The usage of waste material in stabilization has been introduced due to sharp increase in price of stabilizing materials like cement, lime etc and increase in construction cost. To avoid these problems, wastes generated from the industries, agricultural areas can be used to stabilize the soil. It will give a best solution and alternative way to dispose the wastes and clear the environment surroundings in a beneficial manner. 1.3 Rice Husk Ash (RHA) Rice Husk Ash (RHA) is one of the agricultural waste produced in our country when the rice is milled from paddy. About 108 tonnes of rice hsuk is produced in our world annually. Rice husk consists of about 67-90% of silica. The silica is present in this rice husk in amorphous form and it is considered to be a pozzolanic material. It has been estimated that 1000 kg of of rice produce 200 kg of rice husk from which 40 kg of rice husk ash would be generated. The rice husk ash is obtained by burning the rice husk in a 3512

3 kiln at a temperature of about 6000ºC for 24 hours. Since the silica is present in amorphous form, it reacts with CaOH and liberates the heat and forms the cementitious compounds. Rice Husk is shown in Figure 1 and the relevant Rice Husk Ash is shown in the following Figure 2. Figure 1- Rice Husk Figure 2- Rice Husk Ash 1.4 Lime In this study, lime is used as binding material in small amount to increase the strength of the soil satisfactorily. Lime is nothing but Calcium oxide or Calcium hydroxide. When the lime reacts with the soil, there is exchange of cations in adsorbed water layer which results in decrease in plasticity of soil. The lime is more friable and it is more suitable to use in subgrade. In my project work, the lime is added at a constant rate with the soil mixed with RHA and the improvement in strength is evaluated. 1.5 Objective of Study This experimental study focused on the effect of RHA and lime on index and geotechnical properties of the soil and its performance on the subgrade. Rice Husk Ash is added as partial replacement material with variation of percentage as 2.5%, 5%, 7,5%, 10% in steps of 2.5% and the lime is added as a binding material at constant percentage of 2% to enhance the strength and stability of the soil. The laboratory tests are carried out and the effect on soil properties such as Particle size distribution, Atterberg limits, field density, optimum moisture content, Maximum dry density, California Bearing ratio, Unconfined compressive strength is determined in both natural soil and soil mixed with RHA and soil mixed with RHA and lime.from the above experimental investigations, optimum value of percentage addition of RHA with black cotton soil is evaluated and suggest to pave way for the construction of pavement subgrade. 2. MATERIALS USED 2.1 Black Cotton Soil Sample For the experimental work, the soil sample is collected from the canal banks of Kalingarayan Channel in Karungalpalayam village in Erode District, Tamilnadu. About 100 kg of sample is collected and brought to the soil mechanics laboratory in our college for the project work. Standard test on the soil is carried out in our laboratory with the 3513

4 collected soil sample and properties of the soil are determined. The property of the soil is tabulated in Table 1. Table 1- Properties of Black Cotton Soil Soil Properties Test Results Specific gravity 2.51 Liquid Limit (%) Plastic Limit (%) Plasticity Index (%) Shrinkage Limit (%) Free Swell Index (%) IS Classification CH (High Plasticity) Grain Size analysis-percent passing 75µ sieve 89% Optimum Moisture Content (%) 12 Maximum Dry Density (g/cc) 1.03 Insitu Soil Density (g/cc) 1.59 California Bearing Ratio (%) 2.05 Unconfined Compressive Strength (KN/m 2 ) Rice Husk Ash Rice husk is obtained from milling of rice. The material contains silica in huge amount which also refers to be a good pozzolanic material. Being a pozzolana, it reacts with soil in stabilizing process and makes it provide long life durable subgrade in roads. For the project work, the rice husk sample is obtained from the agricultural areas near Pallipalayam Village, Kombanaipudhur in Erode District, Tamilnadu. The samples are collected in three gunny bags. It is then sieved to remove the vegetative and dust particles and then burnt at high temperature to get powdered ash. Then it is cooled for about three hours and taken to the laboratory for determining its chemical composition. The Chemical composition of rice husk ash (RHA) is tabulated in Table 2 Table 2-Chemical Composition of RHA Chemical Parameters Composition Value (%) Silica Aluminum 3.50 Ferric Oxide 1.32 Calcium Oxide 1.57 Magnesium Oxide 1.20 Sodium 0.15 Potassium 0.24 Loss on ignition 0.67 Also the geotechnical properties of the soil are found out. Since the rice husk ash is to be added in partial replacement material in soil to improve its strength, it must also have the 3514

5 similar properties as like the soil sample. Therefore RHA sample is observed in the soil mechanics laboratory and its geotechnical properties is tabulated in Table 3. Table 3-Geotechnical Properties of RHA Properties Test Results Specific gravity 2.4 Liquid Limit (%) 49.4 Plastic Limit (%) Plasticity Index (%) Water Content (%) Optimum Moisture Content (%) 14 Maximum Dry Density (g/cc) Lime Lime is used as a binding material in small amount in this research. It provides an economical way of stabilization being less susceptible to water content. For the work, lime is used in sludge form taken from a industry in Puliyur village in Karur District, Tamilnadu. The Chemcial composition of the lime is tabulated in Table 4. Table 4: Chemical Composition of Lime Chemical Parameters Composition Value (%) Calcium Oxide Silica 3.50 Alumina 1.32 Iron Oxide Magnesia METHODOLOGY The soil sample and the perspective stabilizing sample is collected and sieved through 0.075mm aperture before use. Then its oxide composition is found out. And then, preliminary test are done on the soil sample and the stabilizing material to analyze the similarities in the geotechnical properties. The laboratory tests done to determine the properties include Particle size distribute on, Consistency Limits (Atterberg Limits), Insitu soil tests etc. The Standard Compaction test was done to find the optimum moisture content needed for the CBR test specimens. In the second phase of work, the Rice Husk ash is added to the soil from2.5% to 10% at an interval rate of 2.5% and lime is added at constant percentage rate of 2%. By this partial replacement being done in the soil, California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) of the natural soil and soil mixed with RHA and soil mixed with RHA + lime is comparatively studied by this experimental work and result is analyzed for effective strength increment and reduction in construction cost and to provide green environment. 3515

6 4. EXPERIMENTAL PROGRAM RESULTS AND DISCUSSIONS 4.1 Compaction The standard compaction test is done according to the procedures given in the relevant Indian Standard Codes. The test is done to determine the variation in optimum moisture content and maximum dry density in natural soil and RHA mixed soil with 2% of lime. The Dry density of soil sample increases with the increase in moisture content in natural soil to a certain limit and get decreased after reaching the maximum dry density value. When the RHA mixed soil is compacted, the maximum dry density decreases with increase in moisture content with increase in RHA content. The decrease in MDD explains that the RHA is a light weight material with low specific gravity and more voids. So it absorbs water more in the void space provided. Hence more water is added to compact RHA mixed soil. Therefore lime is added to decrease the water content and increase the MDD of the soil in a good way. The variations in MDD and OMC with the nature soil and RHA mixed soil is shown in Figure 3 and Figure 4 and Figure 5 respectively. 1.2 MDD Dry Density (g/cc) % 8% 10% 12% 14% 16% MDD Figure 3-Variation of MDD in Black Cotton Soil sample MDD Dry Density (g/cc) % 5% 7.5% 10% MDD Figure 4- Variation of MDD in RHA mixed soil sample 3516

7 Optimum Moisture COntent (%) 25% 20% 15% 10% 5% 0% 2.5% 5% 7.5% 10% OMC 10% 14% 16.70% 19.10% Figure 5- Variation of OMC in RHA mixed soil sample 4.2 California Bearing Ratio This is also one of the common tests done to evaluate the strength of stabilized soils, This CBR value is widely used in the design of base course and sub base course in pavement construction. The variation of CBR with RHA content addition from 2.5% to 10 is shown in Figure 6. For the unsoaked soil samples, the value of CBR has slight increase with addition of 2.5% of RHA and raises more at 5% RHA. The value of CBR drops down at 7.5% and 10% of RHA. The decrease in CBR value is due to clay content reduction in soil. This results in reduction of cohesive force in the soil sample. Initially RHA with high silica content forms the cementitious compound giving the good cohesion. When the RHA content increases in the soil, it slows down the pozzolanic reaction by occupying the void spaces in the soil and reducing the bond between soil and RHA mixtures. California Bearing ratio (%) OMC CBR 2.5% 5% 7.5% 10% CBR Figure 6-Variation of CBR in RHA mixed soil sample 3517

8 4.3 Unconfined Compressive Strength This method is also used to evaluate the strength of stabilized soils. This test is mostly recommended to find out the amount of stabilizing material required in soil stabilization. The variation of UCS of the soil stabilized with RHA-lime admixture is shown in Figure 7. The UCs value increased with increase in RHA content at percentage intervals from 2.5% to 10%. The UCS value of the natural black cotton soil was found to be 250 KN/m 2. With the addition of 2.5% of RHA, the UCS value increased to 269 KN/m 2. On Further addition of 5% of RHA to the soil, the UCS value increased to 286 KN/m 2. After that, the UCS value decreases with addition of RHA content in the soil. This is because of the similar reasons said above in the CBR test itself. On excess addition of RHA, the reaction between the CaOH in the soil and rice husk ash becomes slow which results in weak bonding between soil-rha mixtures. To improve the strength of soil and RHA admixture, addition of lime is considered. Lime is added at a constant rate of 2%. On reaction of lime with silica, it produce cementitious material and binds together with the soil. With the addition of lime to Soil-RHA mixture, UCS value gets increased to 350 KN/m 2. But the addition of lime more than 2% with RHA is not beneficial in strength increment. Unconfined compreessive Strength (KN/m2) UCS 2.5% 5% 7.5% 10% Rice Husk Ash (%) Figure 7- Variation of UCS in RHA mixed soil sample 5. CONCLUSION In this experimental study, the effect of RHA on geotechnical properties of the expansive soil are investigated and analyzed. From the results obtained, it can be concluded there is little improvement in the usage of RHA stabilized soil. The conclusion to the study is summarized as follows: The specific gravity of the soil decreases with the addition of RHA to the soil. The liquid limit and plastic limit of the soil increases with the percentage increase of RHA. It was also observed that the maximum dry density (MDD) of the soil decreases with the addition of RHA due to lower specific gravity of RHA. The optimum moisture content (OMC) of the soil increases on stabilizing with RHA due to pozzolanic reaction between CaOH of the soil and RHA. The shrinkage limit of the soil decreases with the increase of 3518

9 RHA. The swelling nature of the soil decreases with the addition of RHA which reduces the formation of cracks on the pavement surface. The CBR and UCS value gets increased to high limit at an optimum value of 5% of RHA content and 2% of lime. It is also be concluded that for the improvement in strength using stabilization in practical purposes, these optimum percentage values of RHA and lime can be recommended for construction. But addition of lime and RHA beyond this limit to the soil is not beneficial and workable. 6. REFERENCES [1] Aparna Roy (2014), Soil Stabilization using rice husk ash and cement, International Journal of Civil Engineering Research, ISSN , Vol 5 Number 1 pp [2] Grytan Sarkar, Md.Rafiqul Islam, DR.Muhammed Alamgir, Interpretaion of Rice Husk Ash on Geotechnical Properties of BC soil, Global Journal of Researches in Engineering,Volume 12 Issue 2 Feburary [3] B.Sunnel Kumar, Preethi, Behaviour of expansive soil stabilized with rice hsukash &lime, International Journal of Engineering Trends and Technology, Vol 11 No.1, May 2014 pp ) [4] J N Jhaand and K.s Gill (2006), Effect of rice husk ash on lime stabilization, Journal of the Institution of Engineers (India),Vol 87, Issue 28, pp [5] IS 2720 (Part- 5,7,10), Indian Standard Methods of Tests for Soils. [6] S.M.Prasanna Kumar (2012), Silica and Calcium effects on Geo-tech Properties of Expansive soil extracted from Rice Husk Ash and Lime, International Conference on Environment Science and Engineering, Vol 32 pp [7] Air F Haji, A Adnan and Chew K C (1992),Geotechnical properties of a chemically stabilized soil from Malaysia with rice husk ash as an additive, Journal of Geotechnical and Geological Engineering, 10,No.2,pp [8] Agarwal, B. M. (1989). Utilization of rice husk ash. Assumption University journal of Thailand, 12(2): [9] Akshaya Kumar Sabat, Engineering Properties of an Expansive soil Stabilized with Rice husk ash and Lime sludge International Journal of Engineering and Technology (IJET), Vol 5, No.6 Dec 2013-Jan