Stabilization/Solidification and Micro-Structural Analysis of Pond Ash Using Lime

IJBSTR RESEARCH PAPER VOL 1 [ISSUE 8] AUGUST 2013

ISSN 2320 – 6020

Stabilization/Solidification and Micro-Structural Analysis of Pond Ash Using Lime Barkha Tripathi and S. M. Ali Jawaid* ABSTRACT: Recycling of waste material is one of the effective solutions of its disposal problem. Fly ash generated by coal-based thermal power plant takes huge amount of land for disposal and creates environmental problem. From each power station, thousands of tons of fly ash are pumped in to the ash ponds in the form of slurry. Solidification/stabilization of fly ash improves the geotechnical properties and reduces the adverse effect to the environment. This paper shows the laboratory test results of Class C pond ash mixed with small amount of lime, and local soil. In the present investigation, various tests were conducted on soil sample mixed with various percentages of fly ash and lime. The result reveals that the optimum content of admixture for achieving maximum strength is approximately 92% pond ash mixed with 3% lime. Scanning Electron Microscope imageries were also confirmed that change in structure due to stabilization.

KEY WORDS: Solidification/stabilization, Scanning Electron Microscope, Lime, Recycling, Compaction, CBR, Pond ash INTRODUCTION In India’s power production programmed coal based thermal power plants are major player. According to Central Electricity Authority of India upto March 31, 1998 total 82 coals fired power plant existing in India. Fly ash produced by thermal power plants creates environmental problem and requires huge disposal area. There are generally three category of coal ashes are available from thermal power stations such as (1) Dry fly ash (2) Bottom ash (3) Pond ash (Bera et al., 2007).

The fly ash produced from the burning of pulverized coal in a coal-fired boiler is a finger grained powdery particulate material that is carried off in the flue gas and usually collected from ESP (Electrostatic Precipitator) or mechanical device. Ashes collected at the bottom of the boiler furnace are called as bottom ash which possesses better geotechnical properties. Fly ash and bottom ash are mixed together with water in the form of slurry which is pump to ash pond area.

Previous researchers studied different uses of fly ash such as bulk fill material (Raymond 1958; DiGioia and Nuzzo 1972; Gray and Lin 1972; Joshi et al. 1975), soil stabilization (Chu et al.1955; Goecker et al. 1956; Viskochil et al. 1957; Vasquez and Alonso 1981), and land reclamation (Kim and Chun 1994) Author: Barkha Tripathi currently Department of civil EngineeringMadan Mohan Malaviya Engineering College Gorakhpur Uttar Pradesh 273010, E-mail: me_barkhacs@rediffmail.com

Potential application of fly ash alone or soil stabilized with fly ash or fly ash and admixtures for road construction has been reported by a number of researchers (Ghosh et al. 1973; Manjesh et al.2003; Satyanarayana Reddy and Rama Moorthy 2004; Ghosh and Subbarao 2006). Jute-geo textile reinforcing fly ash was found to be a promising technique to improve the bearing capacity of the foundation medium (Ghosh et al.

2005).

Actually, two classes of fly Ash are defined by ASTM C618: Class F Fly Ash and Class C Fly Ash. The main difference between these classes is the amount of calcium, silica, alumina, and iron content in the ash. The chemical property of the fly ash is highly influenced by the chemical content of the coal burned. The free content of fly ash contributes to selfhardening, fraction of lime, present as free lime in the form of calcium oxide or calcium hydroxide, controls self-hardening characteristics of fly ash. In this paper, the strength of pond ash and ash mixed with soil with lime and stabilized soils have been investigated.

2. MATERIALS AND METHODS SOIL The investigations contained in this work have been carried out using soil obtained from Madan Mohan Malaviya Engg .College, Gorakhpur. The geo technical properties and OMCMDD curve of soil are given in Table1and Graph 1 respectively.

*Co-Author: S.M.Ali Jawaid is currently Associate Professorin Department of civil engineeringMadan Mohan Malaviya Engineering CollegeGorakhpur Uttar Pradesh -273010, Email: smaj@rediffmail.com

Table 1:

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IJBSTR RESEARCH PAPER VOL 1 [ISSUE 8] AUGUST 2013

ISSN 2320 – 6020 The Soil was stabilized with either by Pond ash or Pond ash mix with lime to compare its behavior with non-stabilized soil.

Firstly, Pond ash in different percentage (40%, 87%, 92%, 97%, 100%) mix with different percentage of soil (57%, 10%, 5 %.) with 3% Lime Content are shown in Table 4. The Standard Proctor Compaction test was carried out to know the optimum moisture content (OMC) and maximum dry density (MDD) of various mixes. In order to prepare the sample for CBR test in soaked condition, the different mixes thoroughly mixed with water to obtain optimum moisture content of the respective mix, and kept inside the soaking for periods 2-4 days in order to allow the moisture equilibrium to take place.

Graph 1: Proctor’s Compaction Test on Soil

Table 4: Designation of Various Mix Proportions of SoilPond Ash-Lime

Pond Ash In this study, Pond Ash, which is Class C category, was taken from Panki Thermal Power Station, Kanpur. The chemical composition and physical properties of Pond ash and OMCMDD curve are given in Table 2, Table 3 and Graph 2 respectively.

Table 2: Chemical Composition of Fly ash

The test for Grain Size Distribution, Specific gravity, Atterberg Limit, Compaction Parameters and California bearing ratio (CBR) were conducted as per relevant I.S Codes.

The various mixes of soil- Pond ash-Lime (M2, M3, M4, M5) were prepared and corresponding to maximum strength and CBR value that is 92% Pond ash+5% Soil+3% Lime.

Table 3: Physical Properties of Pond ash

Graph 3: Compaction Test Result of Stabilized Soils LIME

Graph 2: Proctor Test on Pond Ash

Lime used in this research is a commercial lime;it is a white, caustic, and alkaline crystalline solid at room temperature. The long term performance of any structure or construction depends on the soundness of underlying soils, because unstable soils creates significant problem for structural.

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IJBSTR RESEARCH PAPER VOL 1 [ISSUE 8] AUGUST 2013 Scanning Electron microscope The SEM analysis was carried out to study the morphology of the samples. This test was carried out Birbal Sahani Institute of Palaeobotny (BSIP), Lucknow. The gold coated samples were place inside the SEM chamber for micrograph. The micro images were taken different at magnifications (1000X, 3000X and 5000X) and analysis of the physiomorphological changes that had occurred due to the stabilization.

3. TEST RESULTS AND DISCUSSIONS Though, the pond ash is non plastic, it exhibits liquid limit due to the fabric effect. Its specific gravity is also low as compared to the virgin soil due to presence of cenospheres (Pandian, et. al., 1998). Table 5 shows the results of compaction test and California bearing ratio (CBR) tests for various mixes of stabilized soil.

ISSN 2320 – 6020 STUDY OF SCANNING ELECTRON MICROGRAPH IMAGERIES Fig 5 shows the SEM view at 3000X of soil compaction on OMC which is 14.9%. It is clearly seen from the picture that there is large number of voids and loose packing of soil grains which could be the reason for its permeability and less strength in structure. Being less in strength makes it unfit for use in many Geotechnical engineering works.

Scanning electron micrograph shows that the addition of lime to pond ash produces a compact matrix on OMC 30.7%. The arrangement of particles in the Fig 6 and Fig 7 is viewed at a magnification of 3000X under the scanning electron microscope. It is clearly seen from the picture that there is less number of voids and tight packing of pond Ash, Soil and Lime max. It could be the reason for less permeability and high strength which shows the improvement of soil properties.

From Table 5,it is evident that the optimum moisture content (OMC) of the soil increases from 20.8% to 30.7%, and the maximum dry density gradually decreases from 1.50 g/cc to 1.182 g/cc, when the soil is stabilized with pond ash to pond ash-lime mixes. So, from Table 5 it is also observed that with increases in pond ash content the maximum dry density decreases. It’s due to the fact that pond ash has hollow structure and thus has low density.

Table 5: Test Result for soil and various mixes

Table 5 and Fig 4 presents the results of CBR test, which are clearly shows that the addition of pond ash and pond ash mix with lime to the soil has influenced soaked CBR value. The CBR value increases approx 8.5% than that of soil alone in soaked conditions at 40% of pond ash and 3% of lime with further increases in pond ash beyond 40%, the CBR value decreases. Further increase of pond ash was resulted in reduction of CBR value. Maximum dry density decreases and CBR increases in all cases. The CBR value of pond ash blended soil increases with increase in percentage of pond ash.

Any further increase in pond ash was leaded to no further increase in CBR.

Fig. 5: SEM image of soil AT 3000X magnification

Fig. 4: Variation of CBR with Pond ash % content

Fig. 6: SEM of 92% Pond Ash+5% Soil+ 3% Lime

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IJBSTR RESEARCH PAPER VOL 1 [ISSUE 8] AUGUST 2013

Fig. 7 SEM of 40%Pond ash +57% Soil+3% Lime

ISSN 2320 – 6020 4.

Kate, J.M. (2005). Strength and volume change behavior of expansive soils treated with fly ash. Geo Frontiers, ASCE, Geotechnical Special Publication.

5.

Pandian, N.S., Rajasekhar, C., and Sridharan, A. (1998).Studies on the specific gravity of some Indian coal ashes. Journal of Testing and Evaluation, ASTM, Vol. (26), 177-186.

6.

Pandian N.S. and Krishna K.C. (2001). CBR behavior of fly Ash murmur mixes. Ground Improvement, 5, 177-181.

7.

Singh, D. N. (1996). Influence of chemical constituents on fly ash characteristics. Proceedings of IGC, IIT Madras, 1, 227 – 230.

8.

Toth, P. S., Chan, H. T. & Cragg, C. B. (1988). Coal ash as a structural fill with specific reference to Ontario experience. Canadian Geotechnical Journal, 25, 694–704.

9.

Viskochil, R. K., Handy, R. L, & Davidson, D.T. (1958).Effect of Density on Strength of Lime-Fly ash Stabilized Soil. Highway Research Building Bulletin183.Washington, D.C, 5-15.

CONCLUSIONS: Based on the experimental study of pond ash content using lime, the following conclusions can be drawn: a.

With an increase in pond ash and pond ash-lime content, the optimum water content increases and the maximum dry density decreases.

b.

Mixture of 92% Pond ash+5% Soil and 3% Lime gives optimum strength of pond ash.

c.

At optimum content of pond ash mixed with soil, lime, the CBR value of stabilized soil increases8.5 times than that of virgin soil alone in soaked condition.

d.

10. Yudhbir&Honjo, Y. (1991). Application of geotechnical engineering to environmental control.

Proceedings ofthe 9th Asian Regional Conference on Soil Mechanicsand Foundation Engineering, Bangkok, 2, 431–466 11. Dharavath, Kishan (2010). “Strength, Durability and Micro-structural Analysis of stabilized Fly Ash” on Indian Geotechnical Confrence-2010.

Due to SEM test, it is clearly seen that there is large number of voids and loose packing of soil grains which could be the reason for its high permeability and less strength in structure. Being less in strength makes it unfit for use in many Geotechnical engineering works.

REFERANCES 1.

Bell F.G. (1996). Lime stabilization of clay minerals and soils. Engineering Geology, 42, 223–237.

2.

Gray D.H. & Lin Y.K. (1972). Engineering Properties of Compacted Fly Ash. Jl. of SMFE, Proc.

ASCE, 98,361-380.

3.

Joshi R.C., Duncan D. M. &Mc Master H.M. (1975).

New and Conventional Engineering Uses of Fly Ash. Jl. of Transportation Engg. Proc. ASCE, 101, 791806.

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