Improvement of Strength of Expansive soil with waste Granulated Blast ...

GeoCongress 2012 © ASCE 2012

Improvement of Strength of Expansive soil with waste Granulated Blast Furnace Slag Anil Kumar Sharma1 and P.V. Sivapullaiah2 1

Research Scholar, Department of Civil Engineering, Indian Institute of Science, Bangalore-560012, Karnataka, India; PH (+91) 9535145760; email: [email protected]. 2 Professor, Department of Civil Engineering, Indian Institute of Science, Bangalore560012, Karnataka, India; PH (+91)-80-22932672; email: [email protected] ABSTRACT Utilization of industrial waste materials in the improvement of problematic soils is a cost efficient and also environmental friendly method in the sense that it helps in reducing disposal problems caused by the various industrial wastes. The main objective of the present study is to improve various engineering properties of the soil by using waste material Ground Granulated Blast Furnace Slag (GGBS) as an alternative to lime or cement, so as to make it capable of taking more loads from the foundation structures. This paper reports the findings of laboratory tests carried out on local Indian expansive black cotton soil with GGBS mixed with the expansive soil in different proportions. The specimens compacted to their respective Proctor’s optimum moisture content and dry density (which varied from mixture to mixture) were cured for a period of 7, 14 and 28 days and their unconfined compression strengths were determined. It is observed that the strength improvement depends on the amount of GGBS used and the effect of curing period is less pronounced. Further it was shown that the initial tangent modulus values generally increases with increase in GGBS content. INTRODUCTION Expansive soils cause major damage to property. These soils contain mineral such as montmorillonite clays that is capable of absorbing water. When they absorb water they increase in volume. The more water they absorb the more their volume increases. This change in volume can exert enough force on a building, sidewalks, driveways, basement floors, pipelines and even foundations to cause damage. These distress problems have resulted in loss of billions of dollars in repairs and rehabilitation (Nelson and Miller 1992).While mechanical compaction, dewatering and earth reinforcement can improve the strength of the soils, other methods like stabilization using admixtures are more advantageous. Various admixtures available are lime, cement, fly ash, blast furnace slag etc. Cement and lime stabilization have been widely used to improve the strength of the expansive soils (Yong et al. 1996; Du et al. 1999). But cement and lime being costlier these days increase the overall cost of the project. Therefore research has concentrated on reducing the cost of the binders. Another issue that the world is facing today is the disposal of industrials wastes like Fly ash, Ground granulated blast furnace slag (GGBS). There is a great need to utilize

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these wastes in a beneficial way. Several projects have illustrated that successful waste utilization (e.g. combining industrial waste with additives like lime) could result in considerable savings in construction costs (Kamon and Nontananandh 1991). Swelling in most soils can be controlled by converting the soil to a rigid or granular mass, the particles of which are sufficiently strongly bound to resist the internal swelling pressure of the clay. The addition of industrial products like fly ash, GGBS along with lime produces a high concentration of calcium ions in the double layer around the clay particles, hence decreasing the attraction of water. Also the pozzolanic compounds bind soil particles to improve the strength and decrease swelling. It also promotes the flocculation of dispersed clay particles. Scope and present study Considerable research has been done on fly ash for the stabilization of expansive soils. Sridharan et al. (1997) have studied the effect of fly ash on the unconfined compressive strength of Black Cotton soils found in India which is typically an expansive soil. They have shown that fly ashes increase the strength of BC soil significantly mainly by pozzolanic reactions. Nalbantoglu (2004) studied the effect of Class C fly ash on expansive soil and shown the improvement in the plasticity characteristics of the expansive soil. Only few studies have been done to check the effectiveness of GGBS in the Black cotton Soils (BC soils). Cokca et al. (2009) have carried out experiments to determine the effect of GGBS on grain size distribution, Atterberg limits, swelling percentage and rate of swell of soil samples. But its effect on strength characteristics is not known. The results showed that GGBS was effective in decreasing the total amount of swell while increasing the rate of swell. In another attempt GGBS was found to be efficient to improve the strength of lime stabilized Kaolinitic clays by partially substituting lime for GGBS (Wild et al. 1998). Recently in UK, red gypsum – GGBS binders were used as soil binders for UK soils and high strength and stiffness were achieved suggesting that these binders could satisfy construction project specifications (Hughes et al. 2011). But not much effort has been made in the past to evaluate the compaction, strength and stiffness characteristics of the GGBS stabilized soils, particularly for expansive soils. Therefore to study the effect of GGBS on BC soils, various laboratory tests have been done on the stabilized GGBS-BC soil mixtures. MATERIALS USED Black Cotton Soil The BC soil was obtained from Belgaum district of Karnataka state, India. It is an expansive soil which contains montmorillonite as the major mineral. Soil has been collected from a depth of 1 m below the natural ground level by open excavation. The soil was dried and sieved through 425 micron IS sieve before its use. Ground Granulated Blast Furnace Slag (GGBS) The GGBS used in this study was collected from the concrete industry where it is being used as partial replacement of cement in the manufacture of concrete.

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Mini Compaction test designed by Sridharan et al. (2005) has been carried out on the soil-GGBS mixtures where the GGBS content varied from 0% to 100%. Unconfined compressive (UCC) strength tests were then done on each of the combinations of soil-GGBS mixtures. This paper presents the details of the Compaction and UCC tests done on the various combinations of the soil-GGBS mixtures. The physical properties of BC soil and GGBS used in the study are listed in Table 1. Particle size distribution details are mentioned in Table 2. Table 1. Physical properties of BC soil and GGBS Properties

Materials BC soil

GGBS

Specific gravity

2.61

2.83

Liquid limit (%)

76

31.5

Plastic limit (%)

35

NP

Plasticity index (%)

41

NP

Shrinkage limit (%)

10

34

Free swell index (cm³/g) OMC (%) MDD (kN/m³)

4.22 32 13.57

0 26 12.75

Table 2. Particle size distribution Constituent Clay content (%) Silt content (%) Fine sand content (%) Soil classification

Materials BC soil 69 27 4 CH

GGBS 0.70 23.0 76.3 -

Proportions of soil and GGBS The BC soil and GGBS were mixed in the dry state in the soil: GGBS in different weight ratios. The water contents at which the samples were mixed were chosen on the basis of the results of the Compaction Tests conducted. The test specimens for UCC test of height 7.6 cm and diameter 3.8 cm were prepared by statically compacting the mixtures in the mould to their respective maximum dry density at corresponding optimum water content. The samples were then cured in desiccators at 100% humidity. The unconfined compressive strength test as per the standard method (ASTM 1989 (Designation D2166-85)) was then done on the cured samples at the


end of the required curing period. A constant strain rate of 0.061 cm/min was maintained for all the samples. Experimental Programme Black cotton soil alone, GGBS alone and mixtures of soil and GGBS in weight proportions of 9:1, 4:1. 7:3, 3:2, 1:1. 2:3, 3:7, 1:4 and 1:9 are compacted to their optimum conditions and cured for 7, 14 and 28 days and their unconfined compressive strength were determined. RESULTS AND DISCUSSIONS Compaction Behavior The results of the Mini compaction test are shown in Fig.1 for all the combinations of the soil-GGBS mixtures. Figures 2 and 3 show the variation of optimum moisture content (OMC) and maximum dry density (MDD) with respect to the GGBS content respectively.

Figure 1. Compaction curves of BC soil with GGBS From the figures 2 and 3, it can be found out that both OMC and MDD decrease almost continuously with increase in the GGBS content with some perturbations. The perturbation for OMC occur with GGBS contents of 70% and 90 % and for MDD with GGBS contents of about 20% and 50%.

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Figure 2. Variation of OMC with GGBS content

Figure 3. Variation of MDD with GGBS content

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Any additive, which increases OMC of soil generally decrease MDD and vice versa. Addition of silt or sand to fine grained soil decreases OMC and increases MDD. Similarly Fly ash addition has been reported to decrease the optimum moisture content and increase maximum dry density (Phanikumar et al. 2005). It is interesting to note that addition of GGBS decreases both OMC and MDD. Addition of any coarser materials GGBS, obviously should decrease OMC due to decrease in clay content of the soil and hence the water holding capacity. There is almost continuous decrease in OMC with increase in GGBS up to about 60% of GGBS. The reduction in OMC with increase in GGBS content beyond 60% is marginal. This suggests that the water holding capacity of the mixture does not decrease probably due to water held in the matrix partly though the adsorbed water by the soil has decreased due to decrease in clay content with increased additions of GGBS. The decrease in MDD, in spite of decrease in OMC, is due to the predominant effect of high frictional resistance offered by coarser GGBS particles due to size and surface texture resisting the compactive effort effectively. However the effect of reduction in water holding capacity and increase frictional resistance are more or less evenly balanced at lower GGBS contents and MDD remains unaffected. With increase in GGBS content beyond 50%, the effect of frictional resistance dominates over the effect of decrease in water holding capacity and MDD decreases. Thus for soil GGBS mixtures the highest value of MDD is obtained at 50% of GGBS. Unconfined Compressive Strength (UCS) The unconfined compressive strength (UCS) of BC soil (Fig.4) increases with the addition of small amount of GGBS up to about 10% GGBS and remains constant up about 40% and thereafter decreases with further increase in GGBS content. The variations in strength can be explained by the following factors: 1. Decrease in the cohesion of the soil due to addition of frictional materials. 2. Improved strength due cementation of pozzolanic compounds produced. 3. The variations in compaction parameters as the soil GGBS mixtures are compacted to their respective Proctor’s optimum conditions. 4. Coating of GGBS by soil particles. With the addition of 10% of GGBS, the reduction in cohesion of soil is less. The reduction in moulding density is also very small. Since the OMC is sufficiently high water is available for pozzolanic reactions to progress sufficiently. With increase in GGBS content the available pozzolanic material increases but the available water for pozzolanic reactions becomes less due decreased moulding water content. These opposing factors compensate and the strength remains more or less unaffected. With GGBS content higher than 40% all the effect of decreased moulding water content and density dominate and the strength decrease. It is interesting to note that the strength of GGBS alone is greater the strength of any soil-GGBS mixture. This shows that GGBS particles are bound by pozzolanic compounds without hindrance by soil particles.

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It can be seen from figure 4 that the effect of curing period is significant for GGBS alone and for any combination soil and GGBS. It is relatively high for GGBS as the water is absorbed by soil and is available for pozzolanic reactions. In some cases there is small decrease in strength if sufficient water is not available for pozzolanic reactions to proceed. The results show that the strength increases with addition of small amount of the GGBS content but decreases further additions.

Figure 4. Variation of UCS with GGBS content Effect of GGBS content on initial tangent modulus of the soil-GGBS specimens In this study the stiffness was represented by the initial tangent modulus calculated from the stress versus strain response of the soil-GGBS specimens. The effect of change in the percentage of GGBS on the initial tangent modulus of the specimens cured for 28 days tested is shown in Fig. 5. It is seen that the initial tangent modulus of the specimens increased with the increase in the GGBS content up to 20%. Beyond this content a marginal decrease in the initial tangent modulus value was observed with further increment in the modulus value.

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Figure 5. Variation of Initial tangent modulus with GGBS content

CONCLUSIONS The following conclusions can be drawn from the experimental results: 1. Both optimum moisture content and maximum dry density decreased with the addition of GGBS to the BC soil. This is due to predominant effects of reduced clay content and increased frictional resisting respectively. 2. The strength increased with the addition of GGBS upto 20% for the curing periods of 7 and 14 days, and up to 40% for the curing period of 28 days. Further addition of GGBS decreases the strength of soil-GGBS mixture. The effect of curing with GGBS content is relatively less pronounced. 3. The improvement in initial tangent modulus with GGBS content is very high up to 20% of GGBS addition but beyond this content the change is very small. REFERENCES ASTM (1989). Standard test method for unconfined compressive strength of cohesive soil. Designation D2166-85. Annual book of ASTM standards. American Society for Testing and Materials, Philadelphia, 04(08), 253-257. Cokca, E., Yazici, V., Ozaydin, V. (2009). “Stabilization of Expansive Clays Using Granulated Blast Furnace Slag (GBFS) and GBFS-Cement.” Geotech Geol Eng, 27:489–499.

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Du,Y., Li, S., Hayashi, S.,(1999). ).“Swelling-shrinkage properties and soil Improvement of compacted expansive soil”,Ning-Liang Highway, China. Engineering Geology, 53 (3–4), 351–358. Hughes, P.N., Manning, D.A.C., Glendinning, S., White, M.L. (2011). “Use of red gypsum in soil mixing engineering applications.” Geotechnical Engineering Journal, ICE, 164(GE3), 223–234. Kamon, M. and Nontananandh, S. (1991). “Combining industrial wastes with lime for soil stabilization.” Journal of Geotechnical Engineering, 117(1), 1-17. Nalbantoglu, Z.,(2004). “Effectiveness of Class C fly ash as an expansive soil stabilizer”. Construction and Building Materials, 18 (6), 377–381. Nelson, J. D., and Miller, D. J.(1992). Expansive soils, Wiley, New York. Panadian, N.S. and K.C. Krishna. (2002). “The Pozzolanic Effect of Fly Ash on the CBR Behaviour of Black Cotton Soil”. J.of Testing and Evaluation, 31(6):1 Phani kumar, B. R., and Sharma, R. S. (2004). “Volume Change Behavior of Fly Ash-Stabilized Clays.” Journal of Materials in Civil Engineering, 19: 67–74. Sridharan, A., Prashanth, J.P., and Sivapullaiah, P.V. (1997). “Effect of fly ash on the unconfined strength of black cotton soil”, Ground Improvement, 1:169-175. Sridharan, A, and Sivapullaiah, P. V. (2005). “Mini Compaction Test Apparatus for Fine Grained Soils”, ASTM Journal of Testing and Evaluation, Vol. 28, pp. 240-246. Wild, S., Kinuthia, J.M., Jones, G.I., Higgins,D.D. (1998) “Effects of partial substitution of lime with Ground Granulated Blastfurnace Slag (GGBS) on the strength properties of lime stabilised sulphate bearing clay soils.” Engineering Geology, 51:37–53. Yong, R.N., Ouhadi, V.R., Mohamed, A.M.O., (1996). “Physicochemical evaluation of failure of stabilized marl soil”, 49th Canadian Geotechnical Conference Frontiers in Geotechnology, 2: 769–776.

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