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.

    0

    20

    40

    60

    80

    100

    0.001 0.01 0.1 1

    Pe

    rce

    nt

    Fin

    er

    (%)

    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

    va...

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