Evaluation of Fly Ash- Calcium Carbide Residue Stabilized Expansive Soil As a Liner Material in Engineered Landfill Akshaya Kumar Sabat Associate Professor Department of Civil Engineering Institute of Technical Education and Research Siksha ‘O’Anusandhan University, Khandagiri Square, Bhubaneswar, India email:
[email protected],
[email protected]
Rajalaxmi Nayak Post Graduate (Geotechnical Engineering) student Department of Civil Engineering Institute of Technical Education and Research Siksha ‘O’Anusandhan University, Khandagiri Square, Bhubaneswar, India email:
[email protected]
ABSTRACT Assessment of the suitability of fly ash -calcium carbide residue stabilized expansive soil as a liner material in engineered landfill has been discussed in this paper. Fly ash and calcium carbide residue in the ratio of 2:1 were added to an expansive soil up to 30% at an increment of 6%. Experiments were conducted to determine the optimum moisture content, maximum dry density, hydraulic conductivity, unconfined compressive strength, and volumetric shrinkage values of the expansive soil- fly ashcalcium carbide residue mixes. Hydraulic conductivity, unconfined compressive strength, and volumetric shrinkage values have been taken as the criteria to judge suitability of the stabilized soil for use as liner material. From the analysis of laboratory test results it is found that the expansive soil stabilized with 24% of fly ash -calcium carbide residue satisfied the criteria for use as a liner material in engineered landfill.
KEYWORDS:
Suitability, Fly ash, Calcium carbide residue, Expansive soil,
Liner material.
INTRODUCTION Engineered landfills are physical facilities designed for the environmentally safe disposal of waste materials. Liner is the most important component of an engineered landfill. Prevention of the passage of leachates into the underlying soil and ground water is the primary function of liner. Liners can be classified in to three groups i) Compacted clay liner ii) Synthetic liner iii) Composite liner. Because of low hydraulic conductivity, high contaminant attenuation, and less cost of - 6703 -
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construction as compared to other types of liners, compacted clays are widely used as liner in engineered landfill. Compacted clay liners should satisfy the following three important criteria i) Hydraulic conductivity (K) ≤ 1× 10-7 cm/sec ii) Unconfined compressive strength (UCS) ≥ 200kPa and iii)Volumetric shrinkage (VS) ≤ 4% for use as waste containment barriers (Daniel and Wu,1993; Benson and Trast, 1995;Tay et al.,2001;Tah and Kabir 2005). Expansive soil is a type of clayey soil, which swells significantly when it comes in contact with water and shrinks when water is evaporated out of it. The strength of expansive soil is very low, the K value of expansive soil is generally higher than1× 10-7 cm/sec, the VS value is more than 4%.Expansive soil does not satisfy the criteria to be used as liner material. Stabilization using solid wastes (Malhotra and John, 1986; Pandian et al., 2001; Murty and Praveen, 2008; Sabat, 2011; Sabat, 2012; Sabat, 2013) is one of the techniques to improve its engineering properties for use as subgrade, sub base, base, and cushion materials. Similar technique is also used to make expansive soil suitable for use, as a liner material in engineered landfill. The positive effects of stabilization using solid wastes with and without binders, to make expansive soil suitable as a liner material in engineered landfill have been well documented in literature. Some of the prominent solid wastes with and without binders which have been utilized to make expansive soil suitable as liner material are, silica fume (Kalkan and Akbulut, 2004), red mud-cement (Kalkan, 2006), cement kiln dust (Oriola and Moses, 2011), rice husk ash and lime sludge (Sabat, 2014).Fly ash (FA) is a solid waste produced from power plants is generally a pozzolanic material. Calcium carbide residue (CCR) is another solid waste produced during the production of acetylene gas from calcium carbide, has high percentage of CaO. Assessment of the suitability of FA- CCR stabilized expansive soil as a liner material in engineered landfill is limited in literature. FA as a pozzolanic material and CCR as a binder can be utilized to modify the geotechnical properties of expansive soil, so that it can be used as a liner material. The objective of the present investigation is to assess the suitability of FA-CCR stabilized expansive soil as a liner material in engineered landfill.
MATERIALS AND METHODS The materials used in the experimental programme are Expansive soil, FA and CCR. Expansive Soil The expansive soil used in the experimental programme was brought from a place approximately 120 km away from Bhubaneswar. The geotechnical properties of the expansive soil are shown in Table1.
Table 1: Geotechnical Properties of Expansive soil Properties 1)Grain Size Analysis Sand size Silt size Clay size 2) Atterberg’s Limit Liquid Limit Plastic Limit Shrinkage Limit
Values 10% 22% 68% 66% 32% 11%
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3)Compaction Properties i)Optimum Moisture 22% Content (OMC) ii)Maximum Dry Density 16.2 kN/m3 (MDD) 4) UCS 102 kN/m2 5)K 2.81X 10-7 (cm/sec) 6) VS 11.8%
Table 2: Geotechnical Properties of FA Properties
Values
1)Grain Size Analysis Sand size Silt size Clay size 2)Compaction Properties i) OMC ii)MDD
14.22% 83.46% 2.32% 24% 12.8 kN/m3
FA used in the experimental programme was collected from a power plant located in Odisha. It is a class –F FA. The major chemical compositions of FA are: CaO-0.89%, SiO2-69.31%, Al2O3- 28.1% Fe2O3-3.69%. The geotechnical properties of FA are shown in Table 2.
CCR The CCR used in the experimental programme was collected from an acetylene gas plant located in Bhubaneswar, India in dry form. It was oven dried for 24 hours at 1000C, then grounded in Los Angeles abrasion machine until the CCR passes through Indian Standard (IS) sieve 425 micron. The major chemical compositions of CCR are: CaO-70.22%, SiO2-5.36%, Al2O3- 2.67%, Fe2O3-3.86%.
Testing Procedure FA and CCR in the ratio of 2:1 were added to the expansive soil up to 30% at an increment of 6% by replacement of expansive soil with FA-CCR mixes. Standard Proctor compaction, hydraulic conductivity (falling head permeability), UCS, and VS tests were conducted on expansive soil-FA-CCR mixes. Hydraulic conductivity and UCS tests were conducted on samples by preparing them at their OMC and MDD and after 7days of curing. The tests were conducted according to the relevant IS Codes. The VS tests were conducted according to the procedure given by Oriola and Moses (2011). After compaction, the cylindrical samples were extruded from the compaction mold and placed in the laboratory bench at uniform temperature to dry naturally for 30 days. Measurement of the heights and diameters were taken accurate to 0.05mm to compute the volumetric shrinkage.
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To study the effect of molding water content on K, UCS and VS, the sample having optimum percentage of expansive soil-FA-CCR decided based on the three criteria of K, UCS and VS for use as landfill liner material, were prepared at the moisture content, OMC, OMC+2%, OMC+4%, OMC-2% and OMC-4%, then experiments were conducted on expansive soil-FA-CCR mixes with the procedure as described above to find its K, UCS and VS.
ANALYSIS OF TEST RESULTS AND DISCUSSION 16.2 16.0
MDD(kN/m3)
15.8 15.6 15.4 15.2 15.0 0
5
10
15
20
25
30
FA-CCR(%)
Figure 1: Variation of MDD with FA-CCR Fig. 1 shows the variation of MDD of expansive soil with FA-CCR. The MDD goes on decreasing with increase in percentage of FA-CCR.
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26.0 25.5 25.0
OMC(%)
24.5 24.0 23.5 23.0 22.5 22.0 21.5 0
5
10
15
20
25
30
FA-CCR(%)
Figure 2: Variation of OMC with FA-CCR Fig. 2 shows the variation of OMC of expansive soil with FA-CCR. The OMC goes on increasing with increase in percentage addition of FA-CCR. 3.00E-007 2.50E-007
K(cm/sec)
2.00E-007 1.50E-007 1.00E-007 5.00E-008 0.00E+000 0
5
10
15
20
25
30
FA-CCR(%)
Figure 3: Variation of K with FA-CCR Fig.3 shows the variation of K of expansive soil with FA-CCR. With increase in percentage addition of FA-CCR, the K goes on decreasing reaches lowest value when the addition of FA-CCR is 30%. The K reaches a value of 0.72×10-7 cm/sec when the percentage addition of FA-CCR increases to 24% and 0.41×10-7 cm/sec when the percentage addition of FA-CCR is 30%. There is
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not any significant decrease in the value of K when the percentage addition of FA-CCR increases to 30% from 24%.
300
UCS(kN/m2)
250
200
150
100 0
5
10
15
20
25
30
FA-CCR(%)
Figure 4: Variation of UCS with FA-CCR Fig.4 shows the variation of UCS with FA-CCR. With increase in percentage addition of FA-CCR, the UCS goes on increasing reaches highest value when the addition of FA-CCR is 24%, thereafter it decreases. The UCS reaches a value of 298 kN/m2 from 102 kN/m2 when the percentage addition of FA-CCR increases to 24%. 12 10
VS(%)
8 6
4 2 0
5
10
15
20
25
FA-CCR(%)
Figure 5: Variation of VS with FA-CCR
30
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Fig.5 shows the variation of VS with FA-CCR. With increase in percentage addition of FACCR, the VS goes on decreasing. The VS reaches a value of 3.6% from 11.8% when the percentage addition of FA-CCR increases to 24% and 2.5% when the percentage addition of FACCR is 30%, there is not any significant decrease in VS when the percentage addition of FA-CCR increases to 30% from 24%. From the analysis of the test results it is found that the sample having 76% of expansive soil and 24% of FA-CCR satisfied the criteria i) K≤ 1× 10-7 cm/sec ii) UCS ≥ 200kPa and iii)VS ≤ 4% for use as a liner material in engineered landfill. 1.50E-007 1.40E-007 1.30E-007
K(cm/sec)
1.20E-007 1.10E-007 1.00E-007 9.00E-008 8.00E-008 7.00E-008 6.00E-008
20
22
24
26
28
30
Molding Wter Content (%)
Figure 6: Variation of K of soil stabilized with optimum percentage of FA-CCR with molding water content Fig.6 shows the variation of K of soil stabilized with optimum percentage of FA-CCR with molding water content. With change in molding water content the K changes. The K being more when compacted at water content dry of OMC as compared to compaction at wet of OMC. The range of water content at which K ≤1×10-7 cm/sec is 22.65%-28.17%. Fig.7 shows the variation of UCS of soil stabilized with optimum percentage of FA-CCR with molding water content. The UCS value is highest when the sample is compacted at a molding water content of OMC. With change in molding water content the UCS changes. The UCS being more when compacted at water content dry of OMC as compared to compaction at water content, wet of OMC. The range of water content at which UCS ≥ 200 kPa is 20.9-28.9%.
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300 280
UCS(kN/m2)
260 240 220 200 180 20
22
24
26
28
30
Molding Water Content (%)
Figure 7: Variation of UCS of soil stabilized with optimum percentage of FA-CCR with molding water content
4.4 4.2
VS(%)
4.0 3.8 3.6 3.4 3.2
20
22
24 26 28 Molding Water Content(%)
30
Figure 8: Variation of VS of soil stabilized with optimum percentage of FA-CCR with molding water content Fig.8 shows the variation VS of soil stabilized with optimum percentage of FA-CCR mixes with molding water content. The VS goes on increasing with increase in molding water content. The range of water content at which VS≤ 4% is 20.9-27.2%.
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Table 3 shows the acceptable range of water content of the expansive soil stabilized with 24% FA-CCR to have i) K ≤ 1× 10-7 cm/sec ii) UCS ≥ 200kPa and iii) VS ≤ 4% for use as liner material in engineered landfill.
Table 3: Acceptable range of water content Range of water content(%) within which K≤ 1× 10-7 cm/sec 22.65-28.17
Range of water content(%) within which VS≤ 4% 20.9-27.2
Range of water content(%) within which UCS ≥ 200kPa 20.9-28.9
Acceptable range of water content (%)
22.65 - 27.2
CONCLUSIONS The following conclusions are done from the study. • The MDD of expansive soil goes on decreasing and OMC goes on increasing with increase in percentage addition of FA-CCR. The MDD reaches a value of 15.2 kN/m3 from 16.2 kN/m3 when the percentage addition of FA-CCR is 30%.The OMC reaches a value of 25.8 % from 22%, when the percentage addition of FA-CCR is 30%. •
The hydraulic conductivity goes on decreasing irrespective of the increase in percentage addition of FA-CCR reaches lowest value when the addition of FA-CCR is 30%.At 24% addition of FA-CCR the hydraulic conductivity value is 0.72×10-7 cm/sec.
•
The UCS goes on increasing with increase in percentage addition of FA-CCR reaches highest value when the addition of FA-CCR is 24%, further addition of FA-CCR decreases the UCS.The UCS reaches a value of 298 kN/m2 when the addition of FA-CCR is 24%.
•
The volumetric shrinkage goes on decreasing irrespective of the increase in percentage addition of FA-CCR reaches lowest value when the addition of FA-CCR is 30%.The volumetric shrinkage reaches a value of 2.5%, when the addition of FA-CCR is 30% and a value of 3.6% when the addition of FA- CCR is 24%.
•
The optimum percentage of FA-CCR in stabilization of expansive soil for use as a liner material in engineered landfill is 24%, having FA=16% and CCR=8%.At optimum percentage of FA-CCR the stabilized soil satisfied the criteria i)K ≤ 1x10-7 cm/sec ii) UCS ≥200kPa and iii) VS ≤ 4%
•
The acceptable range of water content for the mix having optimum percentage of FA-CCR which satisfied the K, UCS and VS criteria for use as a liner material in engineered landfill is, 22.65 - 27.2 %.
REFERENCES 1. Benson, C.H. and Trast, J.M. (1995) “Hydraulic Conductivity of Thirteen Compacted Clays,” Clay Minerals, 43 (6), 669-681.
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2. Daniel, D.E., and Wu, Y. K. (1993) “Compacted Clay Liners and Covers for Arid Sites,” Journal of Geotechnical Engineering (ASCE), 119 (2), 223-237. 3. Kalkan, E. and Akbulut, S. (2004) “The Positive Effects of Silica Fume on the Permeability, Swelling Pressure and Compressive Strength of Natural Clay Liners,” Engineering Geology ,73(1-2),145-156. 4. Kalkan, E. (2006) “Utilization of Red Mud as A Stabilization Material for the Preparation of Clay Liners,” Engineering Geology, 87(3-4), 220-229 5. Oriola, F.O.P. and Moses, G. (2011) “Compacted Black Cotton Soil Treated with Cement Kiln Dust as Hydraulic Barrier Material,” American Journal of Scientific and Industrial Research, 2 (4), 521-530. 6. Pandian, N. S., Krishna, K. C. and Sridharan, A. (2001) “California Bearing Ratio Behavior of Soil/Fly ash Mixtures,” Journal of Testing and Evaluation, 29(2), 220–226. 7. Malhotra, B.R. and John, K.A. (1986) “Use of Lime –Fly Ash-Soil-Aggregate Mix as a Base Course,” Indian Highways, 14(5), 23-32. 8. Murty,V. and Praveen,G. (2008) “Use of Chemically Stabilized Soil as Cushion Material below Light Weight Structures Founded on Expansive Soils,” Journal of Materials in Civil Engineering,20(5),392-400. 9. Sabat, A.K. and Nanda, R.P. (2011) “Effect of Marble Dust on Strength and Durability of Rice Husk Ash Stabilised Expansive Soil,” International Journal of Civil and Structural Engineering, 1(4), 939-948. 10. Sabat, A.K. (2012) “Utilization of Bagasse ash and Lime Sludge for Construction of Flexible Pavements in Expansive Soil Areas,” Electronic Journal of Geotechnical Engineering, 17(H), 1037-1046. 11. Sabat, A.K. and Bose, B. (2013) “Improvement in Geotechnical Properties of an Expansive Soil using Fly ash-Quarry Dust Mixes,” Electronic Journal of Geotechnical Engineering, 18(Q), 3487-3500. 12. Sabat, A.K. (2014) “Stabilized Expansive Soil as a Liner Material in Engineered Landfill,” Proceedings of the 55th Annual Technical session of Institution of Engineers(I), Odisha State Centre, held at Bhubaneswar,168-174. 13. Taha, M.R. and Kabir, M.H. (2005) “Tropical Residual Soil as Compacted Soil Liners,” Environmental Geology, 47, 375-381. 14. Tay,Y.Y.,Stewart,D.I.,Cousens,T.W. (2001) “Shrinkage and desiccation cracking in bentonite-sand landfill liners,” Engineering Geology,60(1-4),263-274.
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