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STABILIZATION OF EXPANSIVE SOIL WITH RICE HUSK ASH, LIME AND

GYPSUM – AN EXPERIMENTAL STUDY

Koteswara Rao. D Pranav. P.R.T Anusha. M

Professor Graduate Students – 2012

Department of Civil Engineering University College of Engineering

JNTUK KAKINADA KAKINADA- 533 003, A.P, INDIA Email : [email protected]

ABSTRACT

The problem with expansive soils has been recorded all over the world. In monsoon they imbibe water and swell and in summer they shrink on evaporation of water there from. Because of this alternative swelling and shrinkage, lightly loaded civil engineering structures like residential buildings, pavements and canal linings are severely damaged. It is, therefore, necessary to mitigate the problems posed by expansive soils and prevent cracking of structures. Many innovative foundation techniques have been devised as a solution to the problem of expansive soils. The chief among them are sand cushion technique, cohesive non-swelling (CNS) layer technique and under reamed piles. Stabilization of expansive clays with various additives has also attained lot of success. In this study, rice husk ash, lime and gypsum are added to the expansive soil which resulted in considerable improvement in the strength characteristics of the expansive soil. KEY WORDS: SBC, MDD, OMC, CNS, CBR, RHA. 1.1 INTRODUCTION Expansive soils have the tendency to swell when they come in contact with moisture and to shrink if moisture is removed from them. These volume changes in swelling soils are the cause of many problems in structures that come into their contact or constructed out of them. The expansive soils in India have liquid limit values ranging from 50 to 100 %, plasticity index ranging from 20 to 65 % and shrinkage limit from 9 to 14 %. The comprehensive review of literature shows that a considerable amount of work related to the determination of deformation characteristics and strength characteristics of expansive soil is done worldwide. From various contributions, the investigations on strength characteristics of expansive soil conducted by S.Narasimharao et.al (1987, 1996); Sridharan et.al (1989); Mathew et.al(1997); G.Raja Sekaran et.al(2002); Ali.M.A. Abd-Allah (2009) are worthy of note. Improving the strength of soil by stabilization technique was performed by Supakji Nontananandh et.al (2004) and Can Burak Sisman and Erhan Gezer(2011). The effect of electrolytes on soft soils were explained by Sivanna, G.S (1976);Anandakrishnan et.al (1966); Saha et.al (1991); Rao, M.S et.al(1992);Sivapullaiah, P.V. et al (1994); Bansal et.al(1996); S. Narasimha Rao et.al(1996); Appamma, P.,(1998); Chandrashekar et.al (1999);G. Rajasekaran et.al (2000); J. Chu et.al (2002);Matchala Suneel et.al (2008). The effect of steel industrial wastes on soft soils were presented by Ashwani Kumar et.al (1998); Bhadra, T. K et.al (2002); Dr. D. D. Higgins (2005); Koteswara Rao (2006). 1.2 OBJECTIVE OF THE STUDY

To study the influence of rice husk ash, lime and gypsum on atterberg limits, compaction, strength, CBR and free swell index properties of expansive soil.

Koteswara Rao. D et al. / International Journal of Engineering Science and Technology (IJEST)

ISSN : 0975-5462 Vol. 3 No. 11 November 2011 8076

1.3 RICE HUSK ASH Rice milling generates a by-product known as husk. This surrounds the paddy grain. During milling of paddy about 78% of weight is received as rice, broken rice and bran. Rest 22% of the weight of paddy is received as husk. This husk is used as fuel in the rice mills to generate steam for the boiling process. This husk contains about 75% organic volatile matter and the remaining 25% of the weight of this husk is converted into ash during the firing process, known as Rice Husk Ash (RHA). This RHA in turn contains around 85% - 90% amorphous silica. So for every 1000 kg of paddy milled, about 220 kg (22%) of husk is produced, and when this husk is burnt in the boilers, about 55 kg (25%) of RHA is generated. India is a major rice producing country and the husk generated during milling is mostly used as a fuel in the boilers for processing paddy, producing energy through direct combustion and/ or by gasification. About 20 million tonnes of RHA is produced annually. This RHA is a great environmental threat causing damage to the land and the surrounding area in which it is dumped.

Lots of ways are being thought for disposing it by making commercial use of RHA.

Table: 1 Chemical composition of rice husk ash

SiO2 86 %

Al2O3 2.6%

Fe2O3 1.8%

CaO 3.6%

MgO 0.27%

Loss in ignition 4.2%

Table: 2 Physical properties of rice husk ash

S. No PROPERTY VALUE 1

Grain size distribution (percent finer than)

4.75 mm 100 2.0 mm 96 0.6 mm 80 0.425 mm 50 0.21 mm 29 0.075 mm 8 2 SPECIFIC GRAVITY 2.01

USES OF RICE HUSK ASH As a stabilizer : The Rice Husk Ash would appear to be an inert material with the silica in the crystalline form suggested by the structure of the particles, it is very unlikely that it would react with lime to form calcium silicates. It is also unlikely that it would be as reactive as fly ash, which is more finely divided. So Rice Husk Ash would give great results when it is used as a stabilizing material. In lightweight fill: The ash would appear to be a very suitable light weight fill and should not present great difficulties in compaction, provided its initial moisture content is kept within reasonable limits (say less than 50%). The very high angle of internal friction of the material will mean that its stability will be high. However, the lack of cohesion may lead to problems in construction due to erosion and shearing under heavy rollers. To overcome these problems, it is desirable to place a 3 to 6 inch thick blanket layer of cohesive material for every 2 to 3 ft. Other uses: The low density of the compacted rice husk ash over a wide range of moisture contents, coupled with small pore size and high permeability should make the material very suitable as a final filter for water supply. Un-burnt rice husk might be used as a first stage filter. Because it is cheaper, it could be replaced frequently, if necessary. The low compacted RHA would suggest its use in light weight concrete.



1.4 MATERIAL USED Expansive soil: The soil used in this study is expansive soil, obtained from NIT Campus, collected at a depth of 1.5m from ground level. The Index & Engineering properties of expansive soil are determined as per IS code of practice and determined & presented in table 3. Rice Husk Ash: Locally available RHA was used in the present work. The physical and chemical properties are determined and presented in table 1and table 2. Lime: The commercial grade lime was used in this present study. Gypsum: The gypsum was collected from Coramandel Fertilizers, Visakhapatnam. 1.5 LABORATORY STUDIES The laboratory studies were carried out on the samples of expansive soil, expansive soil + RHA + Lime mixes and expansive soil + RHA + Lime + Gypsum mixtures. Liquid limit: The liquid limit test was conducted on expansive soil, expansive soil+20% rice husk ash+ 5% lime, using Casagrande’s liquid limit apparatus as per the procedures laid down in IS: 2720 part 4 (1970). Plastic limit: The plastic limit test was conducted on expansive soil, expansive soil+20% rice husk ash+ 5% lime as per the specifications laid down in IS: 2720 part 4 (1970). Shrinkage limit: This test was also conducted on expansive soil, expansive soil +20% rice husk ash+ 5% lime as per IS: 2720 part 4 (1972). Free swell index: This test is performed by pouring slowly 10 grams of dry soil, 10 grams of (soil+ rice husk ash+ lime) passing through 425 micron sieve, in two different 100 cc glass jars filled with distilled water. The swollen volume of expansive soil, expansive soil-rice husk ash-lime mixes are recorded as per IS 2720 part 40 (1985). Final volume – Initial volume Free swell (%) = --------------------------------------- *100 Initial volume Proctor’s standard compaction Test: Preparation of soil sample for proctor’s compaction test was done as per IS: 2720 part-6 (1974). Unconfined compressive strength: The unconfined compressive strength tests are conducted on expansive soil, expansive soil+ rice husk ash+ lime mixes, expansive soil+ rice husk ash+ lime+ gypsum mixture as per IS 2720 part 10 (1973). All the samples are prepared by static compaction using split mould at optimum moisture content and maximum dry density to maintain same initial dry density and water content. The test was conducted under a constant strain rate of 1.5mm/min. The proving ring reading is noted for 50 divisions, and loading was continued until 3 (or) more readings are decreasing (or) constant (or) strain 20% has been reached. The samples of expansive soil and additive mixes were cured for 4 days, 7days and 28days. And at the end of each curing period, three samples for each mix were tested. California bearing ratio Test: The California Bearing Ratio tests are conducted on expansive soil, expansive soil+ rice husk ash+ lime mix, expansive soil+ rice husk ash + lime + gypsum mixtures as per IS 2720 part 16 (1979). The tests were conducted under a constant strain rate of 1.25mm/min. The proving ring reading is noted for 50 divisions, and loading was continued until 3 (or) more readings are decreasing (or) constant. The samples were tested in both soaked and un-soaked conditions. The tests were conducted at time intervals of curing for 4 days, 7days and 14 days at optimum moisture content.



Fig.1 Dry density Vs water content plot for Optimum Moisture Content, Maximum Dry Density of Expansive Soil

0

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

PENETRATION (mm)

LO

AD (Kg)

Fig.2 Load Vs Penetration Plot for California Bearing Ratio (Unsoaked) of Expansive Soil

Table 3: Index and Engineering Properties of Expansive Soil

1.4

1.45

1.5

1.55

1.6

1.65

15 20 25 30DR

Y D

EN

SIT

Y (g

/cc)

WATER CONTENT (%)



0

10

20

30

40

50

60

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

PENETRATION (mm)

LOAD (Kg)

Fig.3 Load Vs Penetration Plot for California Bearing Ratio (soaked) of Expansive Soil

1.6 RESULTS & DISCUSSION

Table 4: Influence of Expansive Soil + Different Percentage of RHA + 5% Lime on Compaction Characteristics.

EXPANSIVE SOIL +%RHA+5%

LIME MIXES MDD (g/cc) OMC (%)

SOIL+10% RHA 1.43 28.2 SOIL+20% RHA 1.24 32.5 SOIL+30% RHA 1.18 40.8 SOIL+40%RHA 1.10 45.4

Sl.No Property Values

1 Gravel (%) 0

2 Sand (%) 29

3 Fines (Silt + Clay) (%) 71

4 Liquid Limit (wL) (%) 50

5 Plastic Limit (wP) (%) 22.5

6 Plasticity Index (PI) 27.5

7 Shrinkage Limit (ws) (%) 14 8 I.S. Classification CH

9 Free Swell Index (%) 100

10 Specific Gravity (G) 2.54

11 Optimum Moisture content OMC (%) 23

12 Maximum dry density MDD (g/cc) 1.6

13 Unconfined Compressive Strength (kPa) 125

14 C.B.R. (Unsoaked) (%) 4

15 C.B.R (soaked) (%) 2



Table 5: Influence of Expansive Soil + 20% RHA + 5% of Lime on

Index and Compaction Properties.

Liquid limit (wl) % 39.2

Plastic limit (wp) % 25.4 Plasticity index(PI) 13.8

Shrinkage limit ( ws) % 19.3 Free swell index (%) 12.5 Specific gravity (G) 2.63

Optimum moisture content (%) 32.5 Maximum dry density (g/cc) 1 .24

Table 6: Influence of Expansive Soil + RHA + 5% Lime on Unconfined Compressive Strength (kpa).

0

100

200

300

400

500

600

700

800

900

0 10 20 30 40 50 Rice Husk Ash (%)

0 2 3 4 5 6 7 Gypsum (%)

UN

CO

NFIN

ED

CO

MP

RE

SS

IVE

STR

EN

GTH

(inK

N/s

qm).

4 Days(RHA)

7 Days(RHA)

28 Days(RHA)

4 Days(GYP)

7 Days(GYP)

28 Days(GYP)

Fig 4: Influence of Curing Period on Combined Effect of Unconfined Compressive Strength of Expansive Soil

The variation of unconfined compressive strength for different percent of rice husk ash + 5% lime of expansive soil is shown in Fig 4. It can be observed that the unconfined compressive strength increase as the curing period increases. The unconfined compressive strength is more for 20% RHA +5% lime addition at 28 days curing period and the value was 583kN / m2 (increased by 366%).

R H A % UCS 4 DAYS CURING

UCS 7 DAYS CURING

UCS 28 DAYS CURING

10 267 382 457 20 304 465 583 30 201 316 423 40 160 225 384



Table 7: Influence of Expansive Soil + 20% RHA + 5% Lime + Gypsum on Unconfined Compressive Strength (kpa).

GYPSUM

% UCS 4 DAYS

CURING UCS 7 DAYS

CURING UCS 28 DAYS

CURING 0 304 465 583 2 323 502 715 3 353 525 810 4 312 496 652 5 308 475 587

The variation of unconfined compressive strength of the expansive soil with addition of 20% RHA+ 5% lime + various percentages gypsum was shown in Fig 4. It was observed that the unconfined compressive strength of the expansive soil increases as the curing period increases. The unconfined compressive strength of the treated expansive soil was more with the addition of 3% gypsum for 28 days curing period.

Table 8: Influence of Expansive Soil + RHA+ 5% Lime on CBR (%).

0

5

10

15

20

25

0 10 20 30 40 50

RICE HUSK ASH (%)

CA

LIF

OR

NIA

BEA

RIN

G R

ATIO

(%

)-

Soaked 4 Days

Soaked 7 Days

Soaked 14Days

Fig 5: Influence of Curing Period on California Bearing Ratio of Expansive soil stabilized with Rice Husk Ash +5 %Lime

With the increase in the percent of rice husk ash for fixed lime percentage, the unconfined compressive

strength of the expansive soil has been increased up to 20% and there by decreased. This was due to the percentage increase of silica in rice husk ash. Due to the cementitious action between clay, rice husk ash and lime, the un-confined compressive strength of the expansive soil was increased. These unconfined compressive

RHA % CBR. 4 DAYS

CBR. 7 DAYS CBR. 14 DAYS

UN SOAKED

SOAKED

UN SOAKED

SOAKED

UN SOAKED

SOAKED

10 12 9 17 14 24 19 20 16 14 20 16 31 22 30 13 11 15 12 19 16 40 10 8 13 10 15 11



strength values were higher for 28 days than 4 days and 7 days, this was due to the pozzolonic action between soil, rice husk ash and lime particles. The addition of small percentage of gypsum makes mixture strong by gaining strength; this was due to further development of pozzolonic action. The variation in California Bearing Ratio value of the expansive soil with the addition of different percentages of rice husk ash + 5% lime was shown in fig 5. It was observed that the California Bearing Ratio increases as the curing period increases. The California Bearing Ratio was more at 20% rice husk ash +5 % Lime for14 days curing period.

Table 9: Influence of Expansive Soil+20% RHA+ 5%Lime+Gypsum on CBR (%).

GYPSUM % CBR. 4 DAYS CBR. 7 DAYS CBR. 14 DAYS

UN SOAKED

SOAKED

UN SOAKED

SOAKED

UN SOAKED

SOAKED

0 16 14 20 16 31 22 2 17 14 24 21 34 26

3 20 18 30 25 36 29 4 19 16 22 19 32 24

5 16 14 20 18 29 21

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6

(%) GYPSUM

CALIF

ORNIA

BEARIN

G R

ATIO

(%

)-

soaked 4DaysSoaked 7DaysSoaked 14Days

Fig 6: Influence of Curing Period on California Bearing Ratio of Expansive Soil Treated with Rice husk ash + 5% Lime + Various percentages of Gypsum

The variation of California Bearing Ratio for 20% rice husk ash+ 5% lime+ different percent gypsum of expansive soil was shown in Fig 6. It was observed that the California Bearing Ratio increases as the curing period increases. The California Bearing Ratio is more at 3% gypsum for 14 days curing period.



0

5

10

15

20

25

30

35

0 10 20 30 40 50

RICE HUSK ASH (%) 0 2 3 4 5 6 Gypsum (%)

CALIF

ORN

IA B

EA

RIN

G R

ATIO

(%

)

Soaked 4Days(Rha)

Soaked 7Days(Rha)

Soaked 14Days(Rha)

Soaked 4Days(Gyp)

Soaked 7Days(Gyp)

Soaked 14Days(Gyp)

Fig 7: Influence of curing period on combined effect of RHA + 5% Lime

+ Gypsum on CBR Values of the Expansive Soil

The increase in percentage of rice husk ash with 5% lime, the CBR values of the expansive soil has been increased up to the addition of 20% RHA +5% Lime and there by decreased. Due to the cementitious action between clay, rice husk ash and lime the CBR values of the expansive soil were increased. These CBR values are higher for 14 days than 4days and 7 days; this is due to pozzolanic action between soil, RHA and lime particles. The addition of small percentage of gypsum reduces the hardening process and helped for further development of pozzolanic action in unsoaked and soaked conditions. Its effect is more in soaked condition, which was due to inter-reaction between silica, lime and gypsum. 1.7 CONCLUSIONS The following conclusions are drawn on the basis of test results obtained on expansive soil stabilized with rice husk ash, lime and Gypsum.

1. It was observed that the liquid limit of the expansive soil has been decreased by 22% with the addition of 20% RHA+5% Lime.

2. It was noticed that the Free Swell Index of the expansive soil has been reduced by 88% with the addition of 20% RHA+5%Lime.

3. It was observed that the unconfined compressive strength of the expansive soil has been increased by 548% with addition of 20% RHA+5% lime + 3% Gypsum after 28 days curing.

4. It was noticed that the CBR value of the expansive soil was increased by 1350% with the addition of 20% RHA+5% lime + 3% Gypsum after 14 days curing.

5. It is observed that there is remarkable influence on strength and CBR values of expansive soil at 20% RHA + 5% Lime + 3% Gypsum which is an optimum percentage.

Rice husk ash can potentially stabilize the expansive soil solely (or) mixed with lime, gypsum. The utilization of industrial wastes like RHA, lime and gypsum is an alternative to reduce the construction cost of roads particularly in the rural areas of developing countries. REFERENCES [1] Ali Jawaid S.M., Shukla. V.K., (1996) “Stabilization of silty sand using RHA and Gypsum” Indian Geotechnical Conference, Madras.

PP 419_421. [2] Gopal Ranjan, A.J.R. Rao, a text book on “Fundamentals of soil mechanics.” [3] IS: 2720 part- 5 (1970): Determination of Liquid limit and Plastic limit. [4] IS: 2720 part- 6 (1972): Determination of Shrinkage limit.



[5] IS: 2720 Part-10 (1973): Determination of Unconfined compressive strength. [6] IS: 2720 part- 6 (1974): Determination of Dry density and Optimum moisture content. [7] IS: 2720 part- 4 (1975): Grain size analysis. [8] IS: 2720 part-40 (1977): Determination of Free Swell Index. [9] IS: 2720 Part-16 (1979): Determination of California bearing ratio. [10] Manjit Singh (2005) “Utilisation of phosphogypsum- a broad review”, [11] The Indian concrete journal pp 40-48 [12] Mohammed Ali and Sreenivasulu.V. (2004) “An experimental study on the influence of Rice husk ash and Lime on properties of

Bentonite”, IGC, Warangal, PP 468-471. [13] Rajesh B. Thakare, O.P Bhatia and K.G. Hiraskar (2001) “Phosphogypsum utilization in India: Literature survey” The Indian concrete

journal PP 408-410. [14] Rama Rao. R and Satyanarayana P.V.V (2003) “use of RHA, Lime and Gypsum in strengthening sub-grade and sub base in low cost

roads” National conference on modern cement concrete and bituminous roads, Vizag PP 374-379. [15] Fidelis O. OKAFOR and Ugochukwu. N. OKONKWO9(2009) Leonardo Electronic Journal of Practices and Technologies. [16] Ghassan Abood Habeeb and Hilmi Bin Mahmud(2011), Study on properties of rice husk ash and its use as cement replacement

material Can Burak Sisman and Erhan Gezer(2011), Effects of rice husk ash on characteristics of the briquette produced for masonry units.

