Stabilization of Soft Soil with Granulated Blast Furnace Slag and Fly Ash

For any civil engineering structure, type and behavior of soil play an important role, as all loads that come from the structure get transmitted to the soil. Soil being a natural material available infinitely below ground level can have different characteristics. Foundation resting on soil for various structures may vary depending upon characteristics of soil. For construction use of soil various methods employed for modifying the properties of soil to its engineering performance. Soft soils show major volume changes due to change in the moisture content. This causes major damage to property constructed on it. These soils contain minerals such as montmorillonite that are capable of absorbing water. When they absorb water their volume increases. Although mechanical compaction, dewatering and earth reinforcement have been found to improve the strength of the soils, other methods like stabilization using admixtures are more advantageous. The different admixtures available are lime, cement, fly ash, blast furnace slag etc. At present cement stabilization nowadays is not preferable because of the increasing cost of cement and environmental concerns related to its production. Lime is also not suitable for soils which contain sulphates. Presence of sulfates can increase the swelling behavior of soil due to the formation of swelling minerals such as ettringite and thaumasite. With these considerations, the requirement of finding the other alternative materials will prove most promising one. This study will be focused on the use of the industrial waste materials like fly ash and GBS. Fly ash is a by-product from burning pulverized coal in electric power generating plants. GBS can be obtained from blast furnace slag, a by-product from the manufacture of iron. Industrial waste materials have little or no production cost. Waste materials utilization will prove not only the promising solutions for disposal problem, but also save construction cost. The main object of this study is to investigate the potential of using industrial waste material in the field of geotechnical engineering. Also in developing countries like India the biggest handicap to provide a complete network of road system is the limited finances available to build road by conventional method, therefore there is a need to resort to one of the suitable method of low cost road construction

The ultimate objective is to improve engineering properties of soil, by using industrial waste, to achieve the specific aim in the field of road construction by achieving economy and by protecting environment.

Gupta and Seehra (1989) studied the effect of lime-GGBS on the strength of soil. They found that lime- GGBS soil stabilized mixes with and without addition of gypsum, or containing partial replacement of GGBS by fly ash produced high UCS and CBR in comparison to plain soil. Cokca (2001) has studied the effect of fly ash on the properties of expansive soil prepared in the laboratory using kaolinite and bentonite. Pandian (2002) conducted laboratory CBR tests on the stabilized fly ash-soil mixtures and found that fly is an effective admixture for improving the soil quality. Sridharan (1997) has studied the effect of fly ash on the unconfined compressive strength of black cotton soils found in India which is typically an expansive soil. Above studies, motivated the authors to investigate the potential of industrial wastes i.e. fly ash and non-grounded granulated blast furnace slag (GBS) to stabilize the soft soil.

The soil is collected from Datala, rural area in Chandrapur district, Maharashtra, India at a depth of 0.4 meter for ground level. Table 1: Properties of soft soil from M.E.L. Chandrapur, Maharashtra, India. Table 2: Properties of GBS

The FA has been collected from super thermal power station Chandrapur, Maharashtra, India. Table 3: Properties of Fly ash Properties of soft soil, GBS and fly ash are determined as per the Bureau of Indian Standard (BIS). Properties of soft soil are tabulated in Table 1 the raw soil was identified as inorganic fine grained expansive soil with blackish gray in color. Table 2 shows the properties of GBS and Table 3 shows the property of fly ash. Fig.1 and 2 shows the dry soil sample and fly ash respectively used in this study, The soil collected from the site was pulverized with wooden mallet to break lumps and then air-dried. Processing of fly ash was done on the similar line as that of raw soil. Oven dried granulated blast furnace slag (GBS) was used for mixing with fly ash-soil mixture. A number of soil-fly ash-GBS combinations were used to determine the compaction and strength properties of blended mixes in accordance with BIS. Table 3 shows the combination of the soil-fly ash-GBS mixes. Total twelve trial combinations were formed, and compaction and strength properties of blended mixes were evaluated in the laboratory.

Fig -1: Dry Soil Sample Fig -2: Fly ash Sample

Compaction test and C.B.R. test are conducted on blended soil as per I.S. 1720. The results of compaction test and unsoaked and soaked C.B.R. test on blended soil for various proportions are tabulated in table no. 4.3.1, 4.3.2 and 4.3.3 respectively. Table shows the result for ―DRY DENSITY‖ & ―OMC‖ for different samples and Graph shows the results of compaction test on various proportions. Table 4: Combinations of additive with soil

Compaction properties i.e. maximum dry density (MDD) and optimum moisture content (OMC) were determined in the laboratory of all trial mixture in accordance with IS: 2720 (Part 8) - 1983. Variations of MDD and OMC of the mixes are shown in figs 5.1. (a) and 5.1.(b) respectively. From the figs, 5.1.(a) and 5.1.(b), it is conferred that OMC increased and MDD decreased with increasing percentage of fly ash - GBS mixtures which is consistent with observations reported by Akinmusuru (1991). The decrease in the MDD can be attributed to the replacement of soil by the fly ash in the mixture which has relatively lower specific gravity (2.09) compared to that of the raw soil which is 2.6. The MDD increases by increasing the content of GBS in fly ash–GBS mixtures. This increase in MDD may be explained by considering the GBS as filler with higher specific gravity in the soil-fly ash voids. The increase in OMC due to addition of fly ash may be caused by the absorption of water by fly ash. This implies more water is needed in order to compact the soil with fly ash mixtures. Fig -3: Variation of MDD with fly ash and GBS mix

Fig -4: Variation of OMC with fly ash and GBS mix

CBR test is one of the common tests for evaluating the strength of stabilized soils. The soaked CBR tests were conducted on samples compacted at OMC, and soaked for 96 hours in accordance with IS: 2720 (Part 16) – 1987. The variation in soaked and unsoaked CBR value with addition of fly ash-GBS mixtures is shown in fig 5.2. (a) and 5.2.(b) respectively, which is consistent with Sharma and Shivapullaiah (2011) and Akinmusuru (1991). Both the soaked and unsoaked CBR of fly ash-GBS mixture increases with the increase in the GBS content. Similar trend have been observed for all other mixtures except fly ash-GBS mixtures with 3% GBS content. With addition of fly ash, CBR value increases and then became constant for 3 % GBS content fly ash-GBS mixtures. From the fig 5.2.(a) and 5.2.(b) it is conferred that soaked CBR value of raw soil increased from 2.58 % to its maximum value of 8.32 % with addition of 3% fly ash and 6% GBS. The same trend has been obtained for the unsoaked CBR also. The initial increase in the CBR is expected because of gradual formation of cementitious compounds between the fly ash-GBS and CaOH present in the soil. The gradual decrease in the CBR is due to excess fly ash-GBS that was not mobilized in the reaction, which consequently occupies spaces within the sample and therefore reduces bond in the soil and fly ash-GBS mixtures. Fig -5: Variation of soaked CBR with fly ash and GBS mix Fig -6: Variation of unsoaked CBR with fly ash and GBS mix

Based on the findings of the present investigation, the following conclusions can be drawn: 1. OMC increased and MDD decreased with the addition of fly ash-GBS mixture to the soft soil, Moreover MDD increased with increase in GBS content in fly ash-GBS mixtures. This is due to predominant effects of reduced clay content and increased frictional resistance respectively. 2. Both the soaked and unsoaked CBR of fly ash-GBS mixture increases with the increase in the GBS content.

as optimum percentage as an additive for the soft soil. Based on the results of this research, it appears that soft soil can be effectively stabilized with the addition of fly ash-GBS mixtures. Fly ash- GBS mixtures can be effectively used in flexible pavement constructed for rural road and also embankment and it can also be used as filling materials.

Akinmusuru, J. O (1991), "Potential Beneficial Uses of Steel Slag Wastes for Civil Engineering Purposes", Resources Conservation and Recycling, Vol. 5, PT1, pp. 73-80.Pandian, IS 2720 (part 16)bureau of Indian standard New Delhi -1965 ―California Bearing Test(C,B,R) IS 2720 part 8 bureau of Indian standard New Delhi-1983 ―determination of water content, dry density relation using heavy compaction‖. IS: 2386 Part III (1963) ―Determination of Specific Gravity‖. IS: 460-1962 ‗Partical Size Distribution‖. IS: 9259-1979 and IS 2720 (part V) 1985 ―DETERMINATION OF LIQUID LIMIT AND PLASTIC LIMIT‘.

Rajasekaran,G.(2005),―Sulphate attack and ettringite formation in the lime and cement stabilized marine clays‖. Journal of Ocean Engineering, 32, pp. 1133–1159. S. Gupta, and S. S. Seehra, (1989), "Studies on Lime- Granulated Blast Furnace Slag as an Alternative Binder to Cement", Highways Research Board, Bulletin, No. 38, pp. 81-97.

Yadu, L.K., Singh, D.V., and Tripathi, R.K. (2011). ―Strength Characteristics of Rice Husk Ash Stabilized Black Cotton Soil,‖ Proceedings of International Conference on Advances in Materials and Techniques for Infrastructure Development (AMTID 2011), September 28-30, Paper No. T022. Yadu, L.K., Tripathi, R.K., and Singh, D.V. (2011). ―Laboratory Performance Evaluation of Stabilized Black Cotton Soil with Rice Husk Ash,‖ Journal of Chhattisgarh Swami Vivekanand Technical University Bhilai, Volume 4, No. 1, pp 50-55.

P.G Student, Department of Civil Engineering, JSPM‘S Imperial College of Engineering and Research, Wagholi, Pune, Maharashra