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INFLUENCE OF RANDOMLY DISTRIBUTED NYLON FIBERS MIXED WITH FLY ASH INBLACK COTTON SOIL Kishan Singh1, Amit Richariya2
1Research Scholar, Dept. of Civil Engineering, SVN University, Sagar (M.P)
2Assistant Professor, Dept. of Civil Engineering, SVN University, Sagar (M.P)
Abstract- Roads constructed over problematic soils such as black cotton (BC) soils pose a threat of early deterioration and reduced lifespan. In the present study the strength behaviour of BC soil mixed with the flyash and the nylon fiber was investigated. The CBR of the soil was determined by conducting three series of tests. In test series-I, tests were carried out on the BC soil mixed with varying percentage of fly ash, from 10% to 40% in succession of 10 % by weight of the raw soil. In test series-II the optimum percentage of fly ash was mixed to the soil and the nylon fibers were mixed. In test series-III, the optimum values of flyash and nylon fiber content was fixed (that contributing to maximum CBR), but the thickness of the soil samples in mould was divided in to two parts, one with Nylon fiber + Flyash + BC Soil and another with Flyash + BC Soil. It was concluded that (i) The mixing of 20 % fly ash has pronounced effect on CBR (ii) At aspect ratio of 40 with 0.75 % fiber content and 20 % fly ash mixed soil, CBR value increased by 4.24 times the CBR of raw soil (iii) A combination i.e. Nylon fiber + Flyash + BC Soil and second is having Flyash + BC Soil in ratio of 1/2:1/2 increased CBR by 3.65 times the CBR value of raw soil.
Keywords: Fly ash, Polypropylene fibers, California bearing ratio (CBR), Black cotton soil (BC)
1. INTRODUCTION 1.1 General
Expansive soils are highly problematic because of the susceptibility of these soils to undergo large changes in volume due to fluctuations in the moisture content. In monsoon seasons, soils imbibe water, swell become soft and capacity to bear water is reduced. In drier seasons, these soils shrink or reduce in volume due to evaporation of water and they become harder. Due to its peculiar characteristic of high plasticity, excessive swelling, shrinkage and low strength when wet, the soil is regarded unsuitable for construction material. Heavy financial investments are required to be made for construction of roads, canals and embankments due to non availability of
suitable soil.
During the last two decades environmental hazards, regulations and heightening of public awareness has made it difficult as well as costly to dispose of the waste materials. Therefore, fly ash may be stabilized through traditional soil stabilization agents such as lime, cement, and chemicals. These materials are costly and inconvenient in handling with fly ash. Now Reinforced fly ash may have a promising potential in the days to come where the fly ash will provide the bulk of the mass and
reinforcement will provide the necessary strength to the geotechnical system.
Modern technique of reinforcement of pavement layers is simpler and more effective. Reinforcement means the inclusion of strips, sheets, nets, mats and grids of metals, and synthetic fibers to reduce the tensile strain.
1.2. Nature and Behavior of Black Cotton Soil
The behavior is attributed to the presence of clay minerals with expanding lattice structure. Among them, montmorillonite also called the smectite group is the most common of all the clay minerals in expansive clay soils. The mineral is made up of sheet like units. The basic structure of each unit is made up of gibbsite sheet sandwiched between two silica sheets.
The spacing between the silica --- gibbsite --- silica sheets depends upon the amount of available water to occupy the space. For this reason, montmorillonite minerals exhibit high shrinkage and swelling characteristics.
Kaolinite is anther most common mineral whose structure is made up of gibbsite sheets (with aluminium atoms at their centres) joined to silica sheets through the unbalanced oxygen atoms at
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the apexes of the silica layer. Due tostrong hydrogen bonds, it is extremely difficult to separate the layers, and as a result kaolinite is relatively stable and eater is unable to penetrate between the layers. So kaolinite shows little swell on wetting. China clay is almost pure kaolinite. Illite is another mineral whose structure is similar to that of montmorillonite except that there is substantial replacement of silicones by aluminum in the tetrahedral layers and Potassium ions are between the layers serving to balance the charge resulting from the replacement and to tie the sheet units together. The cation bond of illite is weaker than the hydrogen bond of kaolinite, but is stronger than the water bond of montmorillonite.
2. MATERIALS, METHODOLOGY AND TEST PROGRAMME: MATERIALS
2.1 General
Before performing the various tests of soil-fiber mix composite, the different individual engineering properties of the soil material like Particle Size distribution, Specific gravity, Atterberg's limits, Compaction characteristics under standard compaction, California Bearing Ratios (Soaked and Un-Soaked) at OMC and Unconfined Compression Strength at OMC have been determined. The density and diameter of the natural fibers were also determined. Three types of sands like
fine sand, silver sand and medium sand have been chosen in this investigation as cohesionless soils because these types of sands are easily available all over India at comparable low cost. The locally available cohesive soil has been chosen in this investigation as this type of soil is mostly available surrounding Kolkata and generally used in making subgrades of local roads.
2.2 Cohesionless Soil (SAND):
Three types of sand locally known as Fine sand, Medium sand, and Silver sand have been used in this experimental study. The reason for choice of these types of sand is primarily for their easy availability in many parts of the country for possible use in practice.
2.3 Physical Characteristics of and Used:
To determine the physical characteristics of three types of cohesionless soil following tests have been conducted.
2.4 Particle Size Distribution
Particle size distribution has been carried out as per I. S. Code 2720, Part- IV, 1985. Grain size distribution curves for the three sands. Characteristics of particle size distribution for the three sands like Fine sand, Medium sand, and Silver sand are furnished
Table 1 Characteristics of Grain size distribution for the three types of sand
Sand type Description D10 D30 D60 Cu Cc Remarks
I
Fine sand with brown colour 0.16 0.23 0.33 2.06 1.00 Poorly graded soil II Medium sand with brown colour 0.29 0.51 0.62 2.14 1.45 Poorly graded soil III Silver sand with whitish gray colour 0.10 0.17 0.22 2.20 1.31 Poorly graded soil
2.5 Specific Gravity test:
Specific gravity test has been carried out for as per I.S. Code 2720, Part III, 1980.
Density bottle method is used for the determination of Specific gravity of these three types of soil. The specific gravity of the Fine sand, Medium sand, and Silver sand are 2.63, 2.65 and 2.54 respectively.
2.6 Direct Shear test:
Direct Shear test has been conducted in the laboratory as per I.S. Code 2720, Part XIII, 1986, to get the angle of internal friction of the three types of
sand used. This test has been carried on sandy soil at OMC. The angle of internal friction (φ) for Fine sand, Medium sand, and Silver sand are 38.8°, 41.7°
and 37.2° respectively.
3. METHODOLOGY 3.1 General
A systematic experimental program has been undertaken to investigate the effect of inclusion of three different types of natural Jute fiber, Coir fiber and Sabai grass fiber of various lengths and proportions with different types of sand
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like, fine sand, medium sand, silver sandand one type of clayey soil. Standard Proctor tests, Soaked and Unsoaked CBR tests at optimum moisture content have been conducted using Proctor mould (Plate 4.4) and CBR mould (Plate 4.5) respectively for different soil-fiber composites as per I.S. codal provision.
Fibers have been randomly mixed in soil to form homogeneous mixture.
3.2 Sample Preparation
The mixing of fibers and soil has been done manually with proper care for preparing homogeneous mixture at each stage of mixing. It has been found that the fibers could be mixed with soil more effectively in the moist state than in the dry state. The tests have been performed for various combinations of soil fiber mixtures, as given earlier. Three different types of natural Jute fiber, Coir fiber and Sabai grass fiber have been purchasing from local market. These fibers have been processed in the
laboratory by drying in sun for several days. After that all these fibers have been cleaned from dust and cut into small pieces of length 5mm, 10mm and 20mm for use as fiber material. These fibers have been randomly mixed with soil to form uniform mixture. Uniform distribution of the natural fiber and soil has been achieved with a consistent mixing procedure. If fibers have been mixed in dry soil, segregation of fiber have been noted. To eliminate this problem, the fiber has been first wetted with required quantity of water, then mix to soil and compacted the soil with light weight rammer (Plate 4.6).
3.2.1 Test Programme:
3.2.2 Total Number of Tests Conducted:
Total numbers of different types of test conducted for cohesionless soils and cohesive soil have been calculated as below and are tabulated in Table 2 and 3 respectively.
Table 2: Numbers of different types of test conducted for cohesionless soils
Name of Test Type of Tests No. of Test
Compaction Standard Proctor Test 111
California Bearing ratio Test Un-soaked CBR Test 111 Soaked CBR Test (4 days) 111 Age effect on fiber-sand mix
composites Soaked CBR test for optimum mix, at 1
month, 3months, 6months and 1 year. 36 Table 3: Numbers of different types of test conducted for cohesive soil
Name of Test Type of Tests No. of Test
Compaction Test Standard Proctor Test 37
California Bearing ratio Test Un-soaked CBR Test 37
Soaked CBR Test (4 days) 37
Compressive Strength Test Unconfined Compressive Strength (UCS)
Test 37
Age effect on Composite Mix (fiber + sand)
Unconfined Compressive Strength Test for optimum mix, after keeping the soil sample at same water content for 1 month, 3months,
6months and 1 year.
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4. EXPERIMENTAL WORK 4.1 Material Used
(1.) Expansive soil- The soil was obtained from agriculture field near Khandwa Road Indore (M.P.) at depth of 0.5 m by random sampling.
(2.) Fly Ash- The fly ash was obtained from Magliyagoan near Indore (M.P.). The fly ashes have low densities generally and as a result are useful for structural fills, highway embankments. The disposal problem of fly ash is sort out also.
(3.) Nylon Fiber was brought from Siyaganj Market in Indore (M.P.).
4.2 Experimental Investigation Programme
In first phase, the physical properties of soil such as grain size distribution, specific gravity consistency limits i.e.
liquid limit, plastic limit and shrinkage limit ,free swell index, MDD-OMC, CBR values are determined.
In second phase, the soil is replaced with fly ash in different percentage i.e. 20%, 40%, 60%, and 80%
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and MDD-OMC and CBR values aredetermined.
In third phase, the optimum value of soil and fly ash mixture is further stabilized with nylon fibers with different
percentage (0.5%, 1%, and 1.5%) &
aspect ratio (40, 50, and 60) and moisture density relation and CBR values are evaluated.
4.3 Tests on Soil
The laboratory tests of soil were done as per IS codes which are given below in Table in 4 Table 4: Properties of Soil
PROPERTIES TEST RESULTS IS CODES USED
Specific Gravity 2.5 IS: 2720 (part III)-1964
IS Classification Soil CI IS: 2720 (part IV)-1965
MDD (gm/cc) 1.2
IS-2720 (part VIII) 1980
OMC % 15
CBR % 2.8 IS 2720 (part XVI)
Liquid Limit % 55 IS: 2720 (Part V)-1985
Plastic limit % 36 IS-2720 (Part V) 1965
Plasticity Index % 19 -
Free Swell Index % 35 IS: 2720 (Part XL) 1977
The Grain size analysis of soil is found by dry analysis. Fig 3.1 shows the grain size distribution curve of soil. The soil is classified as per IS classification is CI.
4.4 Tests on Fly Ash
Table 5 shows the physical properties of fly ash
Table 5: Properties of Fly Ash
The laboratory test is conducted for chemical composition of fly ash. As per results fly ash is classified as Class F Fly ash as lime content is found to be 9.33%. Fig 3.2 Particle size distribution curve of fly ash and it is classified as per IS classification is SP.
4.5 Tests on Soil and Fly Ash Mixtures
The soil is replaced with fly ash in different percentage i.e. 20%, 40%, 60%, and 80%. The MDD-OMC and CBR values of soil fly ash mixture are determined. Table 6. shows properties of soil fly ash mixture.
Table 6: Properties of Soil Fly Ash Mixture
% OF FLY
ASH MDD
(gm/cc) MDD
(KN/M3) OMC
(%) UNSOAKED
(CBR) SOAKED
(CBR)
0 1.33 13.05 15 5 2.8
20 1.48 14.52 17 5.22 2.9
40 1.55 15.21 18 6 3.8
60 1.42 13.93 20 5.88 3.1
80 1.30 12.75 22 4.9 2.32
100 1.12 10.99 24 5.5 3.2
PROPERTIES TEST RESULTS IS CODE USED Specific Gravity 2 IS: 2720 (part III)-1964 IS Classification of Fly Ash SP IS: 2720 (part IV)-1965
MDD (gm/cc) 1.12 IS-2720 (part VII) 1980
OMC % 24
CBR % 3.48 IS 2720 (part XVI)
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From Table 6 plot a graph between MDD-OMC & percentage of fly ash in soil the maximum dry density & optimum moisture content in soil fly ash mixture is worked out. The maximum dry density and optimum moisture content were found to be 1.53gm/cc and 17%
respectively for 35% fly ash in soil.
4.6 Tests on Soil, Fly ash and Nylon Fiber Mixture
From above interpolation, as mentioned in paragraph 3.5 the optimum values of soil fly ash mixture i.e. 65% of soil and 35
% of fly ash is taken for further stabilization of nylon fibers with different percentage (0.5%, 1%, and 1.5%) &
aspect ratio (40, 50, and 60). The MDD, OMC, CBR unsoaked & soaked tests are conducted for the study.
5. ANALYSIS OF RESULTS
From the previous chapter i.e. tests of soil, soil fly ash mixture & soil fly ash nylon fiber mixture results are analyzed in subsequent sections which are as follows.
5.1 Effects of Fly Ash on MDD & OMC From Fig 3.1 the maximum dry density and optimum moisture content are found out as 1.53 gm /cc &17% respectively for 35% fly ash and 65% soil. The MDD value increased initially and then it started decreasing. The MDD was found maximum for 65% soil and 35% fly ash proportion. Increase in the MDD value is due to when fibres was added it occupied the void spaces present in soil fly ash mixture. The value of OMC increases with increase in fly ash content.
5.2 Effects of Fly Ash on CBR tests From Table 6 a graph is plotted between percentage of fly ash in soil & CBR%
(Soaked condition) which are shown in Fig. 1
Fig. 1 Variation of CBR with Fly ash content in soil
From Fig 1, CBR value initially increased with increase in fly ash content and then it started decreasing at slow rate. The maximum CBR value (soaked condition) was found for 65% Soil and 35% fly ash is 3.75 %.
5.3 Effects of Fibers content on MDD- OMC
With the addition of fiber content (by weight) in the blend of soil with 35% of fly ash, the MDD value is decreased for different aspect ratio. The fiber cross- section is circular and surface area is more so when fiber content is increased beyond optimum value more void spaces are created resulting decrease in value of MDD. The value of OMC is increased with increase in fiber content for different aspect ratio.
6 CONCLUSIONS
Based upon the study followings conclusion have been drawn.
1. Addition of fly ash in soil improves the properties of soil. The optimum content of fly ash in soil is found to be 35%.
2. The maximum dry density is found to be 1.53gm/cc & 18 % OMC for 35% fly ash in soil. CBR value is found to be 3.75% which is more than virgin soil.
3. On addition of fibers in soil fly ash mixtures, for different aspect ratio MDD, values decreases but OMC values increases.
4. CBR values increases with increase in fiber content for particular aspect ratio but CBR values decreases with increase in aspect ratio, this is due to increase in resistance to penetration.
5. CBR value is found to be 7.2% for 1.5% fiber content and aspect ratio 40.
6. The regression equations are developed between different aspect ratio & CBR values for particular
fiber content.
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