EFFECT ON CBR VALUE AND OTHER GEOTECHNICAL PROPERTIES OF FLYASH MIXED WITH LIME AND NON-WOVEN GEOFIBRES
Prof. R.D.Gupta*, Javed Alam**, Mohd. Ahmadullah Farooqi**
Formerly Prof. Z.H.College of Engg. &Tech; **Lecturer,CES, University Polytechnic, AMU. Aligarh
Abstract
Thermal Power plants generate different types of ash residues and discharge huge amount of particulate matter and gases. Flyash is the most abundant of all the residues and its disposal not only needs enormous land, water and power resources but it also causes serious environmental hazards. In India about 82 such Power Plants produce about 95 million tons of fly ash per year[5] and the figure is likely to soar. This staggering increase in the production of fly ash and its disposal in ecologically suitable manners has lately become a global concern. Efforts are being done to increase the use of fly ash in every possible way. In this struggle scientists and engineers especially civil engineers are playing a remarkable role. A number of studies have been carried out to determine the influence of randomly oriented non-woven geo fibers on the physical properties of soil and fly ash. However, very few studies have been done to investigate the effect of randomly oriented non-woven geo-fibers on fly ash mixed with lime.
In this paper, results of an experimental study has been presented to determine the effect of randomly oriented non-woven geo-fibers on fly ash mixed with lime on the value of CBR and other geotechnical properties.
key words: Fly Ash, Geo Fibers, CBR Test, Proctor’s Compaction Test
1. Introduction
India’s major source of energy is coal. The estimated current reserves of coal are sufficiently large to meet its demand for the next 250 years[2]. The Indian coal is of low calorific value (2500-3500 Kcal/ kg) and has high ash content (40-45%). Now, with the commissioning of super power plants (1000-2000 MW) and increasing use of coal the production has reached about 95 million tons per year. This astounding increase and alarmingly low percentage of utilization (7.5% in India in 1998)(5) poses a potential threat to environment and economy.
Fly ash is a non-crystalline pozzolanic and slightly cementatious material. On the basis of these properties it can be utilized as a construction material and as a filling material for low lying areas and embankments for roads and railways etc.
2. Review Of Literature
Many researchers have hovered their attention towards finding out various properties of fly ash and have also reasoned the drift in the values from the normal values of soil. Sherwood and Ryley (1966) reported that most fly ashes contain particles that are predominantly silt-sized with some sand-sized particles. Pandian et al (1998) studied the variation of Specific gravity of Indian fly ashes in great detail. Dayal et al ((1989) also reported low values of specific gravity values of flyash. The low values of specific gravity are attributed to particles being hollow spheres or cenosherical. Also there are other factors on which Specific Gravity value depends such as gradation, chemical composition of fly ash, etc. Sridharan et al (1998) have reported the shear strength characterstics of some Indian Fly ashes under various conditions. The use of lime to treat fly ash was suggested by Uppal et al (1968).
3. Material
3.1 Fly Ash
Flyash has been collected from Harduaganj power plant, which is located some 14 km North of Aligarh. It is situated at UpperGangesCanal and generates 440MW of electricity. It uses pulverized coal of almost 40% ash content. It produces both bottom ash and flyash. Of the total ash produced flyash constitutes about 30-60%. As the coal is supplied from 22 different mines of Bihar the chemical properties also vary a great extent. The range of chemical components has been summarized as below.
Table 1: Chemical Properties Of Fly Ash Used:
S. No. / Chemical Components / Range1 / Silicon dioxide / 45-60%
2 / Aluminum oxide / 21-29%
3 / Iron oxide / 5-18%
4 / Sulphur trioxide / About 0.4%
5 / Manganese oxide / 0.2-3%
6 / Calcium Oxide / 0.5-6%
Table 2: The Physical Properties Of Plain Flyash, Determined In Lab Are As Follows:
S. No / Property Name / Value1 / Specific gravity / 1.98
2 / Particle size Distribution / .002-.10mm with over 90% passing through 75 micron I.S. Sieve
3 / Optimum Moisture Content, OMC / 18.2%
4 / Maximum dry density / 1.28 g/cc
Table 3: Geotechnical Properties Of Fly Ash:
S. No / Property Name / Value1 / Grain size distribution
% of Gravel
% of sand
% of silt + clay / Nil
6
94
2 / Coefficient of Uniformity, Cu / 2
3 / Coefficient of Curvature, Cc / 1.13
4 / Specific Gravity / 1.95-2.2
5 / Direct shear test
Cohesion
Angle of Shear resistance / 0.0
27o
6 / Proctor’s Density
Optimum Moisture Content
Max. Dry Density / 18%
1.29 g/cc
7 / Permeability Test
Coefficient of Permeability / 1.3 x10-4 cm/sec
Table 4: Properties Of Geo-Fibres:
S. No. / Property Name / Value1 / Cross Section / Triangular
2 / Diameter / 30-40 Micron
3 / Elongation / >100%
4 / Length / 12mm
5 / Melting Point / 240-260 oC
6 / Softening Point / 220oC
7 / Specific Gravity / 1.4
8 / Tensile strength / 4000-6000 kg/cm2
3.2 Lime
The finely ground Calcium Hydroxide, a laboratory reagent, was used to treat the flyash. Its optimum amount with respect to Optimum Moisture Content and Maximum Dry Density was determined first. It was done through Standard Proctor’s Test or Standard AASHO (T-99) Test.
4. Methods
4.1 Determination Of Optimum Moisture Content And Maximum Dry Density
Light compaction test (IS: 2720-VII) is done to get the values of Optimum Moisture Content (OMC) and Maximum Dry Density (MDD). This test conforms to the specifications of Standard Proctor’s Compaction Test or Standard AASHO (T-99) Test. The curve obtained is as shown in figure 6.
4.2 Determination Of Specific Gravity
Specific Gravity of fly ash is determined by 100ml Density Bottle Method.
4.3 Determination Of California Bearing Ratio
The California Bearing Ratio value is defined as the ratio of the force per unit area required to penetrate a soil mass with a standard piston at a rate of 1.25 mm/ min. to that required for corresponding penetration of standard material. Standard load is defined as the load which has been obtained from the test on crushed stone which is defined as having a CBR of 100%.
The specimens were prepared at Optimum Moisture Content in cylindrical mould used for Modified Proctor’s Compaction Test (Dia.:150 mm; Ht.: 175 mm). The sample was compacted in the mould in three equally thick layers; each layer is compacted by 56 blows imparted by a hammer of 2.6 kg weight. Finally, for penetration test two surcharge disks, each weighing 2.5 kg, were placed over the sample and a plunger, 50 mm in diameter, was used to penetrate the sample at a rate of 1.25 mm/min.
The tests were carried out in three stages.
a)In first stage Standard Proctor’s Compaction test on specimens containing Flyash and lime were observed. And the optimum percentage of lime is noted. (Table no. 5)
b)In second stage CBR value of plain Flyash specimen was determined.
c)In the third stage Specimens were prepared by mixing in Flyash the optimum amount of Lime, as obtained in stage 1, at OMC and the percentage of Geo fibers is varied for different samples and CBR values were observed.(Table no. 6)
5. Results
5.1 Load Versus Penetration Curves
The load-penetration curves for plain and lime treated fly ash with varying percentage of reinforcement were drawn. The curves generally conformed to the standard shape but the initial portion of curves was concave upwards. The curves were then corrected by shifting the origin to the point of intersection of a tangent drawn to the curves at the point of greatest slope with the penetration axis. Corrected loads were read from the corrected curves as shown in figures corresponding to 2.5mm and 5.0mm penetrations.
Table No. 5: Optimization Of Lime With Respect To OMC And MDD.
S.No / Fly ash with varying percentage of lime / Optimum Moisture Content / Maximum dry density1 / 0.5 / 18.46 / 1.16
2 / 1.0 / 19.2 / 1.08
3 / 1.5 / 18.0 / 1.28
4 / 2.0 / 18.4 / 1.17
5 / 2.5 / 20.1 / 0.99
Table No. 6: CBR Test Results For Plain And Reinforced Fly Ash
S. No. / Percentage of geofibres (%) / CBR Value at 2.5 mm penetration / CBR Value at 5.0 mm penetration / Ratio of CBR values of reinforced and lime treated fly ash to plain fly ashAt 2.5mm
penetration / At 5.0 mm penetration
1 / Plain Fly ash / 3.4 / 3.9 / 1.0 / 1.0
2 / 0.1 / 7.4 / 8.1 / 2.2 / 2.1
3 / 0.15 / 10.3 / 12.4 / 3.01 / 3.13
4 / 0.2 / 8.8 / 9.4 / 2.6 / 2.4
5 / 0.25 / 8.4 / 9.2 / 2.7 / 2.5
6. Discussion On Results
It is observed from the CBR test results that the maximum value of CBR is obtained when the fly ash sample is mixed with 0.15% of non-woven geo fibers and 1.5% of lime both by weight of dry fly ash. The relevant graphs and tabulated results of the test are as shown in figures 1-4. The increase in CBR value may be due to shear transfer mechanism which has been induced by the inclusion of Geo Fibers. Furthermore, upon inclusion of more than 0.15% of geo fibers the CBR value tends to decrease which may be attributed to the formation of slip surface on account of increase in quantity of geo fibers. Also larger percentage of geo fiber increases the cost of the project and hence may not be effectively recommended.
7. Conclusion
The Results Show That The CBR Value For Fly Ash Mixed With 1.5% Lime And 0.15% Non- Woven Geo Fibers, Both By Weight Of Dry Fly Ash, Has Increased By 3.01 Times For 2.5 Mm Penetration And 3.13 Times For 5.0 Mm Penetration This Increase In The Value Of CBR Is Quite Encouraging. Lime Treatment Also Increased The Load Carrying Characterstics Of Reinforced Fly Ash Considerably. But, Still Future Of Fly Ash Poses Challenge To Scientists And Technologists To Sound Management Of Fly Ash Disposal And Deposition Techniques. Researchers Need To Focus On Environmental Impact Assessment Of Disposal Of Fly Ash ToAvoid Public Health Hazards, Degrading Of Air And Water Quality And Reduce Adverse Environmental Effects.
8. Graphs
References
- Uppal D. H. and Dhawan P.K.,”A Resume Of The Use Of Fly Ash In Soil Stabilization”, Journal of I.R.C., Vol. XXI-2, September 1968
- Gray, D.H. and LIN. Y.K. (1972) “ Engineering Properties of Fly Ash” ASCE, Journal of SM & FE, Vol. 98, No. 4, pp. 361-380
- Proceedings of the International Conference on Flyash Disposal & Utilization”, at New Delhi, January,1998
- Murthy, A.V.S.R. (1998), “ Utilisation of flyash for Embankment construction”’ Proc. International conference on Flyash Disposal and Utilization, CBIP, Delhi, Vol. 2, pp. 6-14
- Proceedings of the Conference” Flyash Disposal and Deposition-Beyond 2000AD”, at IIT Kanpur, February 1999
- Vimal Kumar, et al, “Fly Ash Disposal: Beyond 2000AD”, Flyash Disposal and Deposition-Beyond 2000AD”, at IIT Kanpur, February 1999
- R.D.Gupta, J. Alam, “Comparative Study Of Seepage Characterstics Of Dadri Flyash, Fine Sand And Coarse Sand”, Journal of The Institution of India, vol. 84, Nov 2003, pp 192-195