Proceedings of Indian Geotechnical Conference December 15-17,2011, Kochi (Paper No.H-098.)
BLAST FURNACE SLAG FOR BULK GEOTECHNICAL APPLICATIONS K.V. Manjunath, Associate Prof. in Civil Engg,, M.S. R.I. T., Bangalore -560 054, email:
[email protected] L. Govindaraju, Assistant Professor, Dept. of Civil Engg., U.V.C.E., Bangalore- 560056 ,email:
[email protected] P. V. Sivapullaiah, Professor, Dept. of Civil Engg., I.I.Sc., Bangalore- 560012 ,email:
[email protected] ABSTRACT: One of the solid wastes generated by industries in huge quantities is Blast Furnace Slag. Very few studies have been reported on use of blast furnace slag in stabilizing the soils. In this study, ground granulated blast furnace slag (an industrial waste) along with hydrated lime is used to stabilize a typical black cotton soil. Detailed experimental investigations have been carried out to know the effectiveness of addition of slag and lime to improve the geotechnical properties of soil. Moist cured cylindrical specimens with height to diameter ratio of 2 are tested for UCC strength after different time periods. It is found that undrained shear strength Su of black cotton soil improved phenomenally after curing for 28 days with 4% lime and 40 % ground granulated blast furnace slag.
INTRODUCTION Today, there is a worldwide interest in new and innovative research, knowledge transfer and best practice regarding the development of new ground improvement methods. With the rise in carbon emissions resulting in global warming and climate change, successful new methods are vital. People have tried using GGBS with small amounts of cement [1,2]. But cement production involves high energy consumption & also large carbon emissions. The production of GGBS involves only 30% carbon dioxide emission compared to cement production. Soil stabilization has been used from historical times using lime [3]. In some cases, excessive swelling was observed in lime stabilized sulfate bearing clay soils. Following this, research was carried out with ground granulated blast furnace slag (GGBS) and it was found that GGBS can reduce the expansive tendencies of lime stabilized sulfate bearing clay soils [4, 5]. Using industrial by-products like fly-ash and GGBS for soil stabilization is gaining momentum [6-12]. At present, year after year, most of the countries including India are producing millions of tonnes of blast furnace slag which is the by-product of steel industries. This is posing a big environmental problem, though ready mix concrete industry is using nearly half of this waste. Blast furnace slag obtained from iron & steel manufacturing industries has potential cementitious reactivity. Hence an attempt has been made to improve the strength and swell behavior of expansive black cotton soil using GGBS in this work. MATERIALS USED Black Cotton Soil: Black Cotton Soil (BCS) was procured from a farm field near Bagalkot in Karnataka. Ground granulated blast furnace slag: Ground granulated blast furnace slag (GGBS) was obtained from Ready Mix Concrete Plant of Ultra Tech cement Ltd.
in Bangalore which had procured it from Bhadravathi Iron & Steel works Ltd. Lime: Commercially available pure hydrated lime Ca(OH)2 with 99% purity was used in this work. EXPERIMENTAL INVESTIGATION Material characterization Black Cotton Soil The physical & engineering properties of the soil are listed in Table 1. The soil is classified as sandy clay of high compressibility (CH) as per Indian Standard classification system (ISCS) Ground granulated blast furnace slag The physical & engineering properties of the slag along with those of soil are tabulated in Table 1. The slag may be classified as low compressible silt (ML). Generally blast furnace slag consists of oxides of calcium, silica, alumina, etc. The percentages of these components vary from slag to slag depending on the composition of iron ores used & the manufacturing process adopted in the steel or iron making industry. GGBS is a very fine powder with a specific surface of 320 – 380 m2/kg similar to Portland cement. If it is activated by a small amount of lime, the slag reacts with water to give cementitious products. Compaction Characteristics Mini compaction tests proposed by Sreedharan and Sivapullaiah [14] were used to determine the compaction characteristics of the soil and slag.
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K.V.Manjunath,.L.Govindaraju &.P.V.Sivapullaiah Specimen preparation Cylindrical specimens with height/diameter ratio of 2 were prepared at OMC using static compaction. The specimens were moist cured for 0,3,7,14 & 28 days. Table 1. Properties of BCS & GGBS Sl. No.
Property /Parameter
1
Specific Gravity
2
Grain size analysis i) % of Sand particles ii) % of Silt size particles iii) % of clay size particles
3
For BCS
For GGBS
2.65
2.825
25.2 34.8 40
It can see that the black cotton soil alone has an undrained shear strength Su of 231 kPa only, whereas it increased with the addition of 20% GGBS without lime to about 600 kPa after curing for 7days and to 1551 kPa after curing for 28 days. But when 40% GGBS without lime is added the Su value was only 370 kPa after 28 days of curing and remained the same even after curing for 28 days. Table 2. Variation of soil strength Su with proportions
76.3 23.0 0.7
Soil + Additives
Average Su in kPa
Black cotton soil only
231
80 % BCS + 20 % Slag + 0 % Lime
1551
80 % BCS + 20 % Slag + 2 % Lime
2134
Atterberg’ Limits Liquid limit, % Plastic limit, % Shrikage limit, %
54.8 33.64 17.45
31.5 NP 34
80 % BCS + 20 % Slag + 4 % Lime
3757
60 % BCS + 40 % Slag + 0 % Lime
780
60 % BCS + 40 % Slag + 2 % Lime
3853
4
Plasticity index, %
16.19
NP
60 % BCS + 40 % Slag + 4 % Lime
4065
5
Free Swell, %
60
zero
6
Compaction characteristics OMC ( % ) Max. dry density ( kN / m3 )
25.8 15.64
22.0 16.3
231
zero
7
Unconfined Compression strength, kPa
Shear Tests Two identical specimens were tested in unconfined compression testing machine after 0 days, 3,7,14 & 28 days. The average values of undrained shear strength Su were calculated for each time period. The various trial proportions of BCS, GGBS & Lime listed below were used. i) 100 % BCS ii) 80 % BCS + 20 % GGBS with 0, 2 & 4 % lime iii) 60 % BCS + 40 % GGBS with 0, 2 & 4 % lime The specimens prepared with the above said proportions were also used for free swell tests & shrinkage limit tests. Free Swell and Shrinkage Tests Free swell index was determined as per IS:2720 (Part 40) 1977 and shrinkage limit as per IS:2720 (Part 6) -1972. RESULTS & DISCUSSIONS For the various proportions of soil, slag and lime, the undrained shear strength Su obtained are tabulated in the Table 2. The variation of axial stress versus percentage strain for black cotton soil only is shown in the Fig.1. The variation of axial stress versus percentage strain for different proportions of GGBS, black cotton soil & lime are shown in figures 2 & 3 and the variation of undrained shear strength Su with time is shown in Fig 4 & 5.
Fig 1. UCC Curve for 100% Black Cotton Soil It is also seen from the Table 3 that the free swell of the soil has been reduced from 60% to about 35% by adding 20% of GGBS without lime and to about 12% by adding 40% GGBS without lime. Addition of 2% lime along with 20% GGBS reduced the free swell to 20% & along with 40% GGBS reduced the free swell to about 12%. But further addition of lime has very little effect or no effect. It can also be seen that, with increase in additives shrinkage limit has increased from about 17% to nearly 42%. This 402
Blast furnace slag for bulk geotechnical applications
also confirms the increased volume stability with the addition of additives (40% GGBS + 4% lime).
Fig. 4. Strength variation of (20% GGBS + 80% B.C.Soil) Fig 2. UCC curves of (20% GGBS + 80% Black cotton soil)
Fig. 5. Strength variation of (40% GGBS + 60% B.C. soil)
Fig 3. UCC curves of (40% GGBS + 60% Black cotton soil) 403
K.V.Manjunath,.L.Govindaraju &.P.V.Sivapullaiah Table 3. Effect of GGBS & lime on shrinkage properties of Black cotton soil % Free Shrinkage Materials used Swell Limit (%) 100% Black cotton Soil
60.00
17.43
80%soil + 20%GGBS + 0%lime
34.71
19.44
80%soil + 20%GGBS + 2%lime
20.00
38.12
80%soil + 20%GGBS + 4%lime
20.00
39.93
60%soil + 40%GGBS + 0%lime
14.28
20.89
60%soil + 40%GGBS + 2%lime
11.75
38.21
60%soil + 40%GGBS + 4%lime
11.45
41.93
4.
5.
6.
7. CONCLUSIONS 1. It is found that when 20% slag & 4 % lime ( 5:1 slag to lime ratio) is added to soil, Su increased phenominally almost by 16 times and with 40% slag & 4 % lime ( 10:1 slag to lime ratio) Su increased by 18 times. 2. It is also observed that the free swell of Black cotton soil which was 60 % has reduced to 11.75 % when we used 40% slag & 2 % lime along with BCS. Thus, we could achieve volume stability also. 3. But using 40% slag & 4% lime along with BCS reduced the free swell to 11.45% only, that is it does not show further reduction in the free swell with higher slag content. 4. Hence, to enhance the utiliation of slag and optimal improvement in properties of soil, it is recommended to use 40% slag & 4 % lime along with Black Cotton Soil. REFERENCES 1. Erdal Cocas, Veysel Yazici, Vehbi Ozaydin (2009) “ Stabilization of Expansive clays using ground granulated blast furnace slag & cement”, Geotechnical & Geological Engineering Journal, Vol.27, pp 489499. 2. Jiang L, Chirdchanin M, Katsutada O (2005) “ Stabilization effects on surplus soft clay with cement & ground blast furnace slag”, Journal of Environmental Sciences, Vol.16, No.3, pp 397-403 3. Brook-Bradley HE ( 1952 ) “Soil-cement roads in Worcestershire”, Surveyor 3, pp 571-573.
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