Permeability Study on Fly Ash and Rice Husk Ash ?· Proceedings of International Conference on Advances…

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Proceedings of International Conference on Advances in Architecture and Civil Engineering (AARCV 2012), 21st 23rd June 2012 489 Paper ID TRA122, Vol. 1 ISBN 978-93-82338-01-7 | 2012 Bonfring Abstract--- When the fluid is ground water, the terms coefficient of permeability (k) is essential to determine. If water is present in the soil mass at or near an excavation elevation, then the water that will flow into the excavation must be accounted for. The greater the coefficient of permeability, the greater the volume of water that must be controlled. Therefore the value of coefficient of permeability will impact both design and construction of soil subgrades for pavements. Permeability value depends on the soil's triangular textural and unified classification. The optimum content for stabilizing soil with fly ash and rice husk ash was obtained on the basis of California bearing ratio (CBR) test. This mixing of admixtures to soil changes the permeability along with other strength properties. In order analyse the effect of admixtures on the permeability of stabilized soil, an laboratory study was conducted on these mixes in the present study. Various other properties like CBR, Atterbergs limits, optimum moisture content & maximum dry density, grain size distribution were also analyzed. Keywords--- Permeability, California bearing ratio (CBR), fly ash, rice husk ash, soil I. INTRODUCTION A. General NY given mass of soil consists of solid particles of various sizes with interconnected void spaces. The continuous void spaces in a soil permit water to flow from a point of high energy to a point of low energy. Permeability is defined as the property of a soil that allows the seepage of fluids through its interconnected void spaces. In order to obtain a fundamental relation for the quantity of seepage through a soil mass under a given condition by Darcys law. Darcys Law states that under steady conditions of flow through beds of sands of various thicknesses and under various pressures, the rate of flow is always proportional to the hydraulic gradient. This principle has been found to be generally valid for the flow of water in soils, except at high Aditya Kumar Anupam, Research Scholar, Transportation Engineering Group, Indian Institute of Technology Roorkee, Uttarakhand, India Praveen Kumar, Faculty, Transportation Engineering Group, Indian Institute of Technology Roorkee, Uttarakhand, India G.D Ransinchung R.N, Faculty, Transportation Engineering Group, Indian Institute of Technology Roorkee, Uttarakhand, India velocities when turbulence occurs. Darcys law is expressed mathematically as = ki where q is the total rate of flow through the cross-sectional area A, and k is the so called coefficient of permeability. The proportionality constant (k) is referred to as the hydraulic conductivity, which describes the ability of a porous material to allow the passage of a fluid, and is not a fundamental property of soil, but depends upon a number of factors. Particle size distribution has a significant effect on the materials permeability, in which the smaller the particles, the smaller the voids between them, and therefore the permeability decreases. On the other hand, particle shape and texture influences permeability. Irregular shape and rough surface texture tend to reduce the flow rate of water through the soil. Void ratio, which is dependent on the way soil is placed or compacted, may affect the flow characteristics in soils and it is used essentially in the formulas used to calculate the permeability. Another factor in controlling the hydraulic conductivity is the degree of saturation. Entrapped air in the soil can block flow lines between particles, thereby appreciably reducing the permeability. The temperature factor affects the physical properties of water such as water viscosity, an increase in temperature causes a decrease in the viscosity of water, i.e. the water becomes more fluid, which tends to affect the measured permeability. For laboratory tests the standard temperature is usually 20c (see Head, K. H., 1992 the second edition). Different techniques are available to determine soil hydraulic conductivity (K). The degree of permeability is determined by applying a hydraulic pressure difference across a soil sample, which is fully saturated and measuring the consequent rate of flow of water (Head, K. H., 1992). Permeability is measured using permeameter device (flexible wall or rigid wall) by constant head test or variable (falling) head test. Constant head permeability test is conducted on highly permeable soil like gravel or sand following ASTM D2434-68 Standard Test Method for Permeability of Granular Soils (Constant Head). It consists of applying a constant head (h) on the sample surface and measuring the time needed for collecting a known amount of water at the tail end. The permeability can be calculated using the equation Permeability Study on Fly Ash and Rice Husk Ash Admixes with Subgrade Soil for Pavement Construction Aditya Kumar Anupam, Praveen Kumar, G.D Ransinchung R.N A Proceedings of International Conference on Advances in Architecture and Civil Engineering (AARCV 2012), 21st 23rd June 2012 490 Paper ID TRA122, Vol. 1 ISBN 978-93-82338-01-7 | 2012 Bonfring where, k = coefficient of permeability (cm/sec), from constant head test Q = quantity of water discharged, cm3 t = total time of discharge, sec A = cross-sectional area of soil sample, cm2 L = length of the sample (cm), and h = Head causing flow (cm) Variable head permeability test is conducted on relatively less permeable soils like fine grained soils. The falling head permeability test determines the permeability of a material by measuring the time required for water level to fall from a known initial head (h1) to a known final head (h2). The permeability is then calculated using the equation where, k = coefficient of permeability (cm/sec), from falling head test a = cross-sectional area of reservoir (cm2) L = length of specimen (cm) A = cross- sectional area of specimen (cm2) h1, h2 = water levels (cm), and t = time required for water falling from h1 to h2 (sec) Various researchers have attempted to measure the coefficient of permeability of subgrade (clayey) materials using laboratory test procedures. Some of the test procedures used and results obtained are summarized below. According to work done by Tavenas, F., et al. (1983), permeability tests in the triaxial cell present many advantages: (1) cells of any dimensions can be built easily to accommodate varying sizes of specimens thus reducing the problem of specimen representativity (2) the possibility to test the clay under effective stresses and back pressures equivalent to the in-situ condition is a distinct advantage and (3) both falling head and constant head tests may be performed. Another observation by Tavenas, F. et al. is that the use of high gradients minimizes the errors due to leakage and volume changes of the specimen. Besides, the complete permeability results may be obtained within a practical time frame. He concluded also that as i (hydraulic gradient) increases, the velocity of the water passage through the specimen will increase and not the material's hydraulic conductivity. One more valuable outcome of Tavenas, F., et al. (1983), is that due to the very low permeability of clays, the measurement of (K) implies the observation of very small flows over extended periods of time. The identification and, if possible, the elimination of errors on the observed flow are key requirements for the accurate evaluation of the permeability of clays. Another study by Mesri, G. and Olson, R. E. (1970) was concentrated on the factors that affect the evaluation of the coefficients of permeability. They observed that the coefficients of permeability of clays are controlled by variables that may be classified as mechanical and physico-chemical. The mechanical variables of main interest are the size, shape, and the geometrical arrangement of the clay particles. The coefficient of permeability maximized if the flow channels consist of many small channels and a relatively few large ones, through which the main flow occurs. Physico-chemical variables exert great influence on the coefficient of permeability by controlling the tendency of the clay to disperse or to form aggregates. A major disadvantage of lab tests is the small sample size. The sample size is only a very small percentage of the overall volume, making the representativeness of the samples questionable in light of a possible scale-dependency of hydraulic conductivity. Thus, there is little value in using small specimens to assess field hydraulic conductivity. This observation was similar to the work conducted by Benson, C. H., et al. 1997, who pointed out that small specimens are too small to adequately represent the network of pores controlling field-scale hydraulic conductivity. The fact of the matter is that measured permeability is controlled by so many factors such as air bubbles, degree of saturation less than 100 %, migration of fines, temperature variations which change the fluid viscosity, unavoidable disturbance, dependency upon properties of pore fluid, and/or small sample size which does not provide representative specimen to the field conditions. II. MATERIAL SELECTION A. Soil Clay of medium compressibility (A-7-6) soil is used for this study. The index properties such as liquid limit, plastic limit, plasticity index and other important soil properties as per AASHTO and United States soil classification systems are presented in Table 1. Figure 1 presents the grain size distribution curves of this soil. Table1: Physical Properties of Soil Properties Values Optimum moisture content (%) 17 Dry density (gm/cc) 1.85 Specific gravity 1.99 Liquid limit (%) 46 Plastic limit (%) 21 Plasticity index 25 Unified soil classification CL AASHTO soil classification A-7-6 Type of soil Clay of medium compressibility Proceedings of International Conference on Advances in Architecture and Civil Engineering (AARCV 2012), 21st 23rd June 2012 491 Paper ID TRA122, Vol. 1 ISBN 978-93-82338-01-7 | 2012 Bonfring Figure 1: Grain size Distribution Curve of Soil B. Fly Ash (FA) Fly ash is a waste by-product from thermal power plant, which use coal as a fuel. Fly ash contains substantial amounts of silicon dioxide (SiO2) and calcium oxide (CaO). Fly ash is a non-crystalline pozzolanic and slightly cementitious material. On the base of these properties it can be converted into meaningful wealth as an alternative construction material in civil engineering works. Fly ash is collected from NTPC Dadri, Ghaziabad, India, during the burning of pulverized coal to produce steam for generation of energy in thermal power stations was collected for the study. The collected fly ash, characterized for physical and chemical properties are reported in Table 2. Table 2: Physical and Chemical Properties of Fly Ash Physical Properties Chemical Properties Property Value Constituents % by weight Type Class F or low lime fly ash Ignition loss 7.6 Specific gravity 2.27 SiO2 61 Liquid limit 47 Al2O3 16.9 Plastic limit Non-plastic Fe2O3 7.24 Optimum moisture content (%) 26 CaO 3.74 Maximum dry density (g/cm3) 1.6 MgO 2.4 Specific surface (cm2/g) 4,220 Na2O3 2.7 Lime reactivity (kg/cm2) 50 K20 1.04 Loss on ignition (%) 7.6 SO3 1.51 C. Rice Husk Ash (RHA) Rice husk ash is a predominantly siliceous material obtained after burning of rice husk in a boiler or an open fire. Lime reactivity test conducted on this ash indicate the fully burned rice husk ash exhibits greater reactivity. This waste material having pozzolonic properties can be utilized in the stabilization for road construction. For this study, rice husk ash was obtained from paddy mill, Roorkee. It was fine grained siliceous in nature light weight and grey in color. The physical properties are given in Table 3. Table 3: Properties of Rice Husk Ash Sr. No. Properties Values 1 SiO2 (%) 72.24 2 CaO (%) 4.12 3 MgO (%) 1.7 4 Fe2O3 + Al2O3 7.2 5 Specific Gravity 1.87 6 Lime Reactivity (kg/cm2) 34 III. LABORATORY INVESTIGATION AND INTERPRETATION OF RESULTS A. Standard Proctor Test The geotechnical properties of soil (CBR, permeability, etc.) are dependent on the moisture and density at which the soil is compacted. Generally, a high level of compaction of soil enhances the geotechnical parameters of the soil, so that achieving the desired degree of relative compaction necessary to meet specified or desired properties of soil is very important. The aim of the Proctor test (moisture-density test) was to determine the optimum moisture contents (OMC) and maximum dry densities (MDD) of both untreated compacted and treated stabilized soil-mixtures. In order to obtain these parameters, heavy compaction test was employed for the mentioned mixture proportions as per IS: 2720 (Part 8). The results for OMC and MDD for soil stabilized with fly ash and rice husk ash are as shown in Figure 3 and Figure 4 respectively. 0204060801000.001 0.01 0.1 1Percent Finer (%)Partical Size (mm)Proceedings of International Conference on Advances in Architecture and Civil Engineering (AARCV 2012), 21st 23rd June 2012 492 Paper ID TRA122, Vol. 1 ISBN 978-93-82338-01-7 | 2012 Bonfring Addition of FA & RHA alters the compaction characteristics of soil sample. The dry density decreases and moisture content increases for both the cases (Figs.3 & 4). Typically, higher the concentration of FA & RHA, the greater the alterations to the compaction characteristics are. The increase of moisture contents is approximately linear with the ash content. Increase of moisture content is more pronounced for RHA than FA for having more surface area than FA. The moisture increase is due to the hydration effect and the affinity for more moisture during chemical reaction process. Decrease in density is directly attributed to the flocculation/aggregation and the formation of cementitious products. B. California Bearing Ratio (CBR) Test The California bearing ratio (CBR) is a penetration test for evaluation of the mechanical strength of road sub-grade and base courses. This test was conducted after 4 days of soaking in water as per IS 2720 (Part 16). The results revealed from the laboratory study are presented in Fig. 5. Figure 5 shows the trend of improvement of CBR values for both FA and RHA admixed soil samples. The rate of gain of soaked CBR values are approximately linear for both the cases. This trend is better maintained for soil sample admixed with FA than the one of RHA. The increase of soaked CBR value for RHA admixed soil sample showed linear relationship with the ash content up to 30% after which this increase is slackened. However, these CBR values are more than that of 30% ash content. The increase of CBR value is attributed to the formations of adhesive hydrated compounds like calcium silicate hydrate and calcium aluminates hydrate gels within the soil mass when fine soil particles comes in contact with calcium ions, alumina and silica present in FA and RHA. C. Permeability test Permeability is a measure of the ease in which water can flow through a soil volume. It is one of the most important geotechnical parameters. However, it is probably the most difficult parameter to determine. In large part, it controls the strength and deformation behaviour of soils. It directly affects the quantity of water that will flow toward an excavation, design of subgrade on permeable foundations and design of the clay layer for a landfill liner. For fine grained soil as use in this study falling head permeability test is done. The permeability test results for soil admixed with FA and RHA are shown in table 4. Table 4: Permeability Results of Soil Admixed with FA and RHA Percentage of Soil Percentage of Ash Permeability (cm/sec) FA RHA 100 0 8.6110-10 8.6110-10 95 5 1.510-9 6.4110-8 90 10 6.510-9 2.7110-8 85 15 4.810-8 8.410-7 80 20 3.2710-7 6.4710-6 75 25 8.610-7 5.810-6 70 30 4.710-6 6.1410-5 65 35 2.5710-5 7.4810-4 0 100 7.510-2 1.510-2 As shown in the table permeability value of soil is 8.6110-10 which is very low with respect to drainage capability of pavement subgrade layer. Hence there is a need to increase the permeability of the subgrade soil for better drainage. Admixing 20% of FA to the soil increases the permeability to 3.2710-7 and 15 % of RHA to the soil increases the permeability to 8.410-7 providing an effective drainage for subgrade soil. Further addition of FA and RHA to the soil keeps on increasing the permeability. IV. CONCLUSIONS Clayey soil selected for this study had poor drainage condition. In order to improve the drainage its permeability needs to be increased. This experimental study was aimed to analyze the effect of admixing FA and RHA on the permeability of clayey soil for improving its drainage properties. The additions of FA to the soil shows increase in OMC from 17 to 26 % for and decrease in dry density from 1.88 to 1.52 gm/cc at varying ash content from 0 to 35 %. Similar results are revealed for soil-fly ash admixture. The addition of fly ash and rice husk ash to the soil increases CBR linearly. However, in case of soil-RHA mixture the rate of increment is nearly constant after 30 % of ash content. This shows that 30 % of RHA can be considered as an optimum content for soil stabilization. Based on the extensive experimental study carried out, it was noticed that the permeability of soil increased on admixing FA and RHA, thereby improving the drainage of pavement subgrade layer. Proceedings of International Conference on Advances in Architecture and Civil Engineering (AARCV 2012), 21st 23rd June 2012 493 Paper ID TRA122, Vol. 1 ISBN 978-93-82338-01-7 | 2012 Bonfring From this study, the FA and RHA may be effectively utilized in soil to improve the permeability and thus improving drainage of subgrade layer. REFERENCES [1] Anupam A. K., Kumar P. and R.N. Ransinchung G.D, A comparative study of sugar cane bagasse ash & fly ash for use in pavement construction international conference of highway engineering, Thailand, Bangkok, pp.469-474 ,April 2012. [2] Benson, C. H., and Trast, J. M., Hydraulic Conductivity of Thirteen Compacted Clays, Clays and Clay Minerals, Vol. 43, No. 6, pp. 669-681, 1995. [3] FHWA, 2006. Geotechnical aspects of pavements, Report FHWA NHI05037, Federal Highway Administration, Washington D. C [4] Head, K. H., Manual of Soil Laboratory Testing, Vol. 2: Permeability, Shear Strength and Compressibility Tests, New York: Halsted Press, 1992-2nd edition. [5] IRC, 2001. Guidelines for the design of flexible pavements, IRC: 372001, The Indian Roads Congress, New Delhi. [6] Kumar, P. and Singh, S. P. (2008). Fiber-reinforced fly ash subbases in rural roads. Journal of Transportation Engineering ASCE, Vol. 134 (4), 171-180. [7] Mesri, G., and Olson, R. E., Mechanics Controlling the Permeability of Clays, Clays and Clay Minerals, Vol. 19, pp. 151-158 (1971). [8] Tavenas, F., Leblond, P., Jean, P. and Leroueil, S., The Permeability of Natural Soft Clays. Part I: Methods of Laboratory Measurement, CAN. GEOTECH. J. VOL. 20, pp. 629-644, (1983).


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