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Performance evaluation of structuralproperties for soil stabilised using ricehusk ashAditya Kumar Anupama, Praveen Kumara & G.D. Ransingchung R.N.a

a Department of Civil Engineering, Indian Institute of TechnologyRoorkee, 247667, Roorkee, Uttarakhand, IndiaPublished online: 11 Mar 2014.

To cite this article: Aditya Kumar Anupam, Praveen Kumar & G.D. Ransingchung R. N. (2014)Performance evaluation of structural properties for soil stabilised using rice husk ash, RoadMaterials and Pavement Design, 15:3, 539-553, DOI: 10.1080/14680629.2014.891533

To link to this article: http://dx.doi.org/10.1080/14680629.2014.891533

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Road Materials and Pavement Design, 2014Vol. 15, No. 3, 539–553, http://dx.doi.org/10.1080/14680629.2014.891533

Performance evaluation of structural properties for soil stabilised usingrice husk ash

Aditya Kumar Anupam∗, Praveen Kumar and G.D. Ransingchung R. N.

Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee – 247667, Uttarakhand,India

(Received 15 April 2013; accepted 31 January 2014 )

The present study aims to stabilise local clayey soil with a varying percentage of rice husk ash(RHA). The RHA was collected from rice milling located near Roorkee city. As this material isabundantly available in the local area, efforts have been made to investigate the potential of theRHA–soil mixtures with respect to shrinkage limits, compaction characteristics, unconfinedcompressive strength (UCS), triaxial test, split tensile strength test and the California bearingratio (CBR) after subjected to different humidity conditions, so as to utilise in road construction,if found suitable. The laboratory results indicate that admixing of RHA decrease the maximumdry density, but increased optimum moisture content with increase in RHA content. Inclusionof RHA not only improved CBR, UCS and split tensile strength of clayey soil but also, shownconsiderable improvement on cohesion and angle of internal friction too.

Keywords: clayey soil; RHA; California bearing ratio; unconfined compressive strength;triaxial test; split tensile strength

1. IntroductionRice husk is profusely available in rice producing countries like China, India, Indonesia,Bangladesh, Brazil and South East Asia. Rice husk is mainly used as a fuel in industries inboilers for process energy requirements and for power generations. Rice husk is a fuel havinghigh ash content, varying from 20% to 25% of rice husk and content having 80–90% of silica. Inthe majority of rice producing countries much of the husk produced from the processing of rice iseither burnt for heat or dumped as a waste. India alone produces around 120 million tons of ricepaddies per year, giving around 24 million tons of rice husk and 4.4 million tons of rice husk ash(RHA) every year (Govindarao, 1980). Farm income can be increased both directly and indirectlyif economically profitable means of utilising rice husk generated are utilised in industry or roadsector. There are many reported uses of rice husk such as a fuel in brick kilns, in furnaces, in ricemills for the parboiling process, as raw material for the production of xylitol, furfural, ethanol,acetic acid, lignosulphonic acids, as a cleaning or polishing agent in metal and machine industryand in the manufacturing of building materials, etc. (Govindarao, 1980).

Indian clayey soils can be problematic for direct utilisation of subgrade construction. Clayeysoil applies to soils that have the tendency to swell when their moisture content is increased.Soils containing the clay mineral montmorillonite generally exhibit these properties. The clayeysoils have a low bearing capacity in the presence of water and more shrinkage cracking in the

∗Corresponding author. Email: addiknit03@gmail.com

© 2014 Taylor & Francis

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dry condition. Admixing some percentage of cement or cementitious material with soil improvesthe bearing capacity, but crack formation due to shrinkage cannot be minimised. Hence, highwayengineers are making a constant effort to find the right material that really has the potential toimprove the bearing capacity as well as improve the shrinkage cracking control. In the presentstudy, efforts have been made similarly in this direction, by utilising RHA as an admixture toimprove and strengthen the properties of clayey soil. The long-term performance of the structuralproperties for soil admixed with RHA was evaluated in the laboratory by conducting tests like theshrinkage limit, standard Proctor, the California bearing ratio (CBR), the unconfined compressivestrength (UCS), triaxial and the split tensile strength test.

2. BackgroundSeveral studies have been carried out on the effectiveness of clay stabilisation by RHA admixing. Inthis context, Basha, Hashim, Mahmud, and Muntohar (2005) studied the stabilisation of residualsoils by chemically using cement and RHA. They evaluated compaction, strength and X-raydiffraction of such properties of the soil. It was observed that cement and RHA reduced theplasticity of soils. In general, 6–8% of cement and 10–15% RHA show the optimum amount toreduce the plasticity of soil. They observed that the addition of cement and RHA increased theoptimum moisture content (OMC) and diminished a certain amount of maximum dry densities(MDDs) that correspond to increased cement and RHA percentage. It has been reported that theoptimum cement content is 8% without RHA. The CBR value determined was maximum at 4%cement and 5% RHA mixtures with soil. According to the compressive strength and plasticityindex parameters, 6–8% of cement and 15–20% RHA showed the optimum amount required toimprove the properties of soil. Muntohar (2011) stabilised clayey soil with lime and RHA mixtureswith plastic waste fibres to improve the tensile strength. The fibre content varied from 0.2% to0.4% by dry weight of soil, and the fibre length was 20 mm. Three sizes of cylindrical specimensviz. 50 mm diameter by 100 mm height, 70 mm diameter by 140 mm height and 150 mm diameterby 300 mm height were tested. The lime used for stabilisation was estimated to be 12% of thedry soil mass and the ratio of the lime to RHA was 1:1. Inclusion of 0.2% and 0.4% plastic wastefibres was able to improve the tensile strength behaviour of the stabilised soil. Higher fibre contentresulted in a higher tensile strength and toughness index of the stabilised soil. Yadu, Singh, andTripathi (2011) investigated the potential of RHA to stabilise black cotton (BC) soil. Soil wasstabilised using different amounts of RHA, as 3, 6, 9, 11, 13 and 15%. The performance of RHAmodified soils were evaluated using different performance tests namely, CBR and UCS. It has beenreported that admixing of 9% RHA improves unsoaked CBR value upto 24%. Further increase ofRHA dosage beyond 24% resulted in the lowering of the CBR value. There was approximately77% increase in UCS at 9% RHA as compared to BC soil. Based on these performance tests, ithas been found that admixing of 9% RHA improves remarkably the strength of BC soil Dimter,Rukavina, and Drag (2011) investigated the effect of fly ash in the cement-stabilised pavementbase course materials. They observed that the amount of fly ash strongly influences the strengthof the stabilised mixes. Increasing the amount of fly ash in the binder leads to a decrease in thecompressive and indirect tensile strengths. El-Aziz and Abo-Hashema (2013) used lime–Homrastabiliser to stabilise clayey soil. They found that 5% lime with 15% Homra (L + H : 5 + 15%)gives improvement similar to lime alone (11% lime). This is a valuable conclusion to reduceusing of lime by increasing the per cent of Homra as waste materials. Behak and Nunez (2013)used RHA as a soil stabiliser with lime. Temperature of burning on the reactivity of RHA andmixtures with sandy soil and lime was investigated. It was found that the maximum UCS value andsplitting tensile strength value corresponds to the 20% RHA with 10% lime mixture at 28 and 56

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Road Materials and Pavement Design 541

days. Sandy soils with RHA and lime ide an alternative material for the sub-base and base layersof low-volume traffic pavements. Camargo, Edil, and Benson (2013) used Class C fly ash forstabilisation of recycled pavement material (RPM) and a road surface gravel (RSG). They foundthat the UCS of RPM and RSG stabilised with fly ash increased with increasing fly ash contentand curing time and plastic strains for RPM and RSG with fly ash were smaller than the plasticstrains of the recycled materials alone. Noor, Aziz, and Suhadi (1993), Mantohar and Hantoro(1999), Chandra, Kumar, and Anand (2005), Alhassan (2008), Brooks (2009), Choobbasti et al.(2010), Seco, Ramirez, Miqueleiz, and Garcia (2011) and Olawale and Oyawale (2012), haveanalysed the suitability of RHA in highway sectors and the usefulness of the same with soil hasbeen recommended for the construction of subgrade or sub-base.

In order to better understand the behaviour of expansive soils admixed with RHA, a series ofexperiments was carried out using clayey soil for different percentages of RHA. Shrinkage limitand compaction behaviour were studied. Shear strength and deviator stress were determined for allthe samples with or without RHA ranging from 5% to 35% by weight of soil. This article mainlydeals with the effect of RHA addition in clayey soil on compaction; shear strength, CBR valueand shrinkage characteristics to assess the usefulness of RHA for modifying the soil structure, toimprove the load bearing capacity.

3. Materials3.1. SoilClay of medium compressibility (A-7-6) soil is used for this study. The index properties such asthe liquid limit, plastic limit, plasticity index and other important soil properties as per AmericanAssociation of State Highway and Transportation Officials (AASHTO) and the soil classificationsystem used in the USA are presented in Table 1. Figure 1 presents the grain size distributioncurves of the soil.

3.2. Rice husk ashRHA is a predominantly siliceous material obtained after burning of rice husk in a boiler or openfire. The lime reactivity test was conducted as per IS: 1727-1967, which indicated that the fullyburned RHA exhibits greater reactivity. This waste material having pozzolanic properties can beutilised in the stabilisation process for road construction. For this study, RHA was obtained frompaddy mill, Roorkee. It was fine grained siliceous in nature light weight and grey in colour. Thechemical composition was determined by X-ray fluorescence analysis. The physical and chemicalproperties are presented in Table 2. Figure 2 presents the grain size distribution curves of the RHA.

Table 1. Physical properties of soil.

Properties Values

OMC (%) 17Maximum dry density (g/cm3) 1.68Specific gravity 2.74Liquid limit (%) 46Plastic limit (%) 21Plasticity index 25Unified soil classification CLAASHTO soil classification A-7-6Type of soil Clay of medium compressibility

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0102030405060708090

100

0.001 0.01 0.1 1 10

Per

cent

Fin

er (

%)

Partical size (mm)

Figure 1. Grain size distribution of soil.

Table 2. Properties of rice husk ash.

Physical properties Chemical properties

Property Value Constituents % by weight

Type Class F or low lime fly ash (FA) Ignition loss 8.2Specific gravity 2.17 SiO2 72.2Liquid limit 78 Al2O3 5.4Plastic limit Non-plastic Fe2O3 2.1OMC (%) 75 CaO 4.1MDD (g/cm3) 1.57 MgO 1.7Lime Reactivity (kg/cm2) 34

0102030405060708090

100

0.1 1 10 100 1000

Per

cent

age

fine

r (%

)

Partical size (µm)

Figure 2. Grain size distribution of RHA.

4. Laboratory investigation and interpretation of results4.1. Shrinkage limit (wS)The opposite effect of shrinking is swelling soil. A volume change soil swells with increasingmoisture content, but it will shrink with decreasing moisture content. Soil shrinkage can causeserious distress to a foundation/structure. The mechanism is the same as the expansive, but inthe opposite direction. When wetter than the wS, the soil is fully saturated, but when drier, thesoil becomes unsaturated. The soil changes to a lighter colour at the wS due to the water recedingwithin the pores. In fact, the volume continues to decrease on drying beyond the wS. As soil is

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Road Materials and Pavement Design 543

dried below the plastic limit it shrinks and becomes brittle until all the particles are in contact andthe soil can shrink no further. This point is called the shrinkage limit. The soil still has moisturewithin it but if any of this moisture is lost by further drying, air has to enter the soil to replace it.This test was conducted as per IS 2720 (Part 6). The variation of wS of soil with the addition ofdifferent percentages of RHA is shown in Figure 3.

Figure 3 shows that the shrinkage limit increases with the percentage increase of RHA. Theincrease of shrinkage limit is apparently linear to the RHA content. This trend is maintained upto30% RHA but beyond 30% RHA, the rate of increase slackened. The increase in the shrinkagelimit with the addition of RHA is mainly due to the flocculation of clay particles caused by thefree lime present in the RHA, resulting in the reduction of friction between the particles and alsodue to the substitution of finer particles of clayey soil by relatively coarser RHA particles.

4.2. Standard proctor testThe geotechnical properties of soil (CBR, UCS, triaxial test, etc.) are dependent on the moistureand density at which the soil is compacted. Generally, a high level of compaction of soil enhancesthe geotechnical parameters of the soil. The aim of the Proctor test (moisture–density test) wasto determine the OMC and MDD of soil-mixtures with or without RHA. In this context, heavycompaction test was employed in accordance with IS: 2720 (Part 8). The OMC and MDD for soilstabilised with RHA are depicted in Figures 4 and 5, respectively.

1517192123252729313335

0 5 10 15 20 25 30 35

Shri

nkag

e lim

it (

%)

% RHA

Figure 3. Shrinkage limit for admixed soil.

15

20

25

30

35

40

45

0 5 10 15 20 25 30 35

OM

C (

%)

% RHA

Figure 4. OMC for admixed soil.

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1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

0 5 10 15 20 25 30 35

MD

D (

gm/c

m3 )

% RHA

Figure 5. MDD for admixed soil.

Present analyses show that, OMC increases with the increase of RHA content (Figure 4). Therate of increase of moisture content is apparently linear and gradual upto 15% RHA content.Beyond 15% RHA content, the rate of moisture content showed a significantly high up to 35%,however, between 30% and 35%, the rate of increase slackened. The increase in OMC on admixingof RHA could be mainly due to increasing demand for water by soil-RHA mixtures for hydrationreaction. Contrary to the admixing of RHA with soil leads to a decrease in dry density. The rateof reductions in dry density with respect to virgin soil for 5%, 10%, 15%, 20%, 25%, 30% and35% are 3.26%, 4.84%, 4.25%, 5.51%, 6.05%, 9.09% and 8.33%, respectively. The decrease inthe MDD was attributed to the replacement of soil by a lighter weight material (RHA). This isattributed to the coating of soil by the RHA which results in large particles with larger voids andtherefore less density.

4.3. California bearing ratio testIt is in essence a simple penetration test developed to evaluate the strength of road subgrades.We determine the resistance of the subgrade (i.e. the layer of naturally occurring material uponwhich the road is built) to deformation under the load from vehicle wheels. Even more simply put,“How strong is the ground upon which we are going to build the road.” Higher the CBR reading,the stronger the subgrade and less thick it is to design and construct the road pavement, this givesconsiderable cost saving. Conversely, low CBR reading indicates the subgrade is weak and thatwe must construct a suitable thicker road pavement to spread the wheel load over a greater areaof the weak subgrade so that the weak subgrade material is not deformed, thereby causing theroad pavement to fail. The samples of soil admixed with RHA content varying from 0% to 35%.These admixed soil samples were kept in the humidity chamber for 7, 14, 28, 56 and 128 daysseparately. After the expiry of 7, 14, 28, 56 and 128 days of humidity curing, these samples wereimmersed in potable water for another 4 days. The CBR test was conducted on these samples inaccordance with IS 2720 (Part 16). The graphical plot of laboratory results is shown in Figure 6.

The influence of RHA on CBR of clayey soil is shown in Figure 6. Addition of RHA upto35% led to increases in CBR in comparison to CBR of neat clayey soil. The increase of CBR onadmixing of RHA is more pronounced upto 25% after which this increased slackened gradually.It has also been observed that CBR increases as the days of curing increases. These increaseswere about 9%, 5.4%, 5.1%, 1.5% and 2.2%, respectively, for 7, 14, 28, 56 and 128 days curingin the humidity chamber with respect to 3 days CBR for 25% RHA. These result analysis impliesthat for RHA admixed soil samples, higher CBR value can be expected from those samples keptin humidity conditions prior to soaking. Maximum CBR was offered by samples kept in the

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Road Materials and Pavement Design 545

0

2

4

6

8

10

12

14

16

0 5 10 15 20 25 30 35

CB

R (

%)

% RHA

3 Days 7 Days

14 Days 28 Days

56 Days 128 Days

Figure 6. CBR for admixed soil.

humidity chamber for 128 days followed by 56, 28, 14, 7 and 3 days, respectively. However, thehighest rate of gain of CBR was observed for those samples kept in the humidity chamber for7 days in comparison to those samples kept for a longer period. Admixing of RHA 10% couldproduce CBR more than 7 on average which is the minimum CBR specified for subgrade layerconstruction. The low CBR of the clayey soil as compared to the RHA admixed soil sample isattributed to its inherent low strength which is due to the dominance of the clay fraction. This isdue to the frictional resistance contributed by RHA in addition to the cohesion from the clayeysoil. Further increase in the RHA percentage causes a reduction in the CBR due to the increasein the cohesionof the decreasing clayey soil content despite the increase in strength owing toincrease in RHA content. The increment in CBR can be attributed to the gradual formation of acementitious compound between the RHA and CaOH when it comes in contact with moisture.

4.4. Unconfined compressive strength testUCS test is the main test recommended for the determination of the required amount of additiveto be used in the stabilisation of soil. The unconfined compression test is a quick, relativelyinexpensive mean to obtain undrained shear strength of cohesive soils. This test is commonlyused in practice because of its simplicity. In most cases, undrained strength results from anunconfined compression test are conservative. The maximum stress measured at failure is equalto two times the undrained shear strength. For conducting the UCS test, the cylindrical specimensof size 50 mm diameter and 100 mm length were prepared at OMC and MDD. After compaction,each sample was immediately placed in a polyethylene bag to maintain the required moisturecontent and then cured for 7, 14, 28, 56 and 128 days to protect the samples from free moisturein a 100% relative humidity chamber at 21◦C, as specified in ASTM D1632-07. The test wasconducted in accordance with ASTM D2166-06. The results of UCS of soil admixed with RHAvarying from 0% to 35% tested at 7, 14, 28, 56 and 128 days curing period are shown in Figure 7.

Admixing of RHA with clayey soil samples showed considerable improvement in the UCS(Figure 6). When the RHA was admixed 5%, 10%, 15%,20%, 25%, 30% and 35%, UCS improve-ments were 41.3%,57.5%, 70%, 76.3%, 81.3%, 76.3% and 47.5%, respectively, at 7 days withrespect to clayey soil samples. Similarly, 55%, 73.8%, 87.5%, 96.3%, 98.8%, 88.8% and 70%improvement on UCS were observed at 14 days for the same RHA replacement level with respectto clayey soil samples. Further improvement was observed for higher curing periods, i.e. 60%,79%, 91.3%, 104%, 106% 97.5% and 72.5%; 71.3%, 90%, 100%, 110%, 112%, 109% and 91.3%;

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80

90

100

110

120

130

140

150

160

170

180

0 5 10 15 20 25 30 35

UC

S (q

u) k

Pa

% RHA

7 Days 14 Days

28 Days 56 Days

128 Days

Figure 7. UCS for admixed soil.

75%, 95%, 105%, 114%, 116%, 111% and 101% for 28 days, 56 days and 128 days, respectively.The trend of increase of UCS on admixing of RHA showed a very cohesive manner. Rapidimprovements were observed upto 25% RHA admixing, after which the improvement slackened.The decrease in the UCS values after addition of 25% RHA may be due to the formation of bondsbetween the soil and the cementitious compound formed (Alhassan, 2008). Marked improvementof UCS on admixing RHA is attributed to higher percentage content of silicon dioxide (72.2%).This high amount of silicon dioxide reacts with calcium for generating pozzolonic materials. Thepozzolanic materials increase the strength of clay–RHA blend. Similar results are also reportedby several other researchers (Alhassan, 2008; Ali & Sreenivasulu, 2004; Brooks, 2009; Jha &Gill, 2006; Muntohar, 2002).

4.5. Triaxial testUnconsolidated undrained (UU) triaxial test are most commonly used for specimen of earth-fillmaterials which are compacted in laboratory under specified conditions of OMC and MDD. Whileother triaxial type consolidated drained (CD) or consolidated undrained (CU) will produce moremeaningful strength parameters. The UU test carried out in the present study was intended as aranking test. It was planned to perform the CD test but during the course of the testing programmeit was observed that saturation of clayey soil took more time to achieve complete saturation. As alarge number of specimens had to be tested, it was decided to conduct UU tests on reconstitutedsoil with or without RHA in accordance with ASTM D 2850–03a. All triaxial tests were conductedat a constant axial strain at 1.25 mm/min under UU condition to simulate the behaviour of soilssubjected to quick loading immediately after construction. The cylindrical test samples were ofdimension 100 mm height and 50 mm diameter. The three different confining stresses of 100, 150and 200 kPa were applied on specimens to obtain a peak deviator stress as shown in Table 3. Therange of confining stresses was chosen to obtain more well defined and accurate plots of Mohrenvelopes to obtain the shear strength parameters cohesion (c) and angle of internal friction (ϕ)of the soils mixed with RHA. The variation of c and ϕ with admixing RHA are evaluated and theresults are as shown in Figures 8 and 9, respectively.

Admixing of RHA shows a positive influence on the deviator stress (Table 3). Higher deviatorstresses are observed for higher RHA content irrespective of the confining pressure applied anddays of curing. However, beyond 25% RHA content, the deviator stress starts declining gradually.Admixing of RHA causes an increase in cohesion and internal friction angle. Increase in cohesionis more pronounced upto 10% RHA content. The cohesion of soil ranges from 28 to 46 kPa and

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Road Materials and Pavement Design 547

Table 3. Deviator stress for admixed soil at different confining pressure.

Deviator stress (kPa)

% RHA Confining pressure (kPa) 7 days 14 days 28 days 56 days 128 days

0 100 204.83 204.83 204.83 204.83 204.83150 276.52 276.52 276.52 276.52 276.52200 337.97 337.97 337.97 337.97 337.97

5 100 285.02 308.67 314.63 331.21 342.18150 376.22 404.35 409.02 427.27 437.99200 470.28 506.21 512.84 536.57 550.91

10 100 312.45 340.31 349.81 363.48 376.85150 409.31 442.41 451.26 465.25 478.60200 506.17 547.90 559.70 577.93 595.43

15 100 331.82 362.89 370.69 388.02 395.87150 431.36 468.13 474.48 492.78 506.71200 537.55 584.25 593.10 616.95 628.44

20 100 350.44 380.52 399.33 414.52 423.50150 459.08 502.29 527.12 538.88 550.55200 567.72 616.45 642.93 663.24 673.36

25 100 359.46 389.16 408.31 418.72 434.62150 460.11 502.02 522.64 540.15 547.62200 578.73 626.55 654.32 667.03 686.70

30 100 352.29 378.09 394.98 420.38 428.50150 450.93 480.18 497.67 525.48 533.48200 567.18 606.84 629.99 664.20 674.03

35 100 292.61 323.13 329.06 356.69 379.68150 377.46 413.61 422.84 449.96 491.68200 471.10 517.01 525.17 565.35 601.79

25

30

35

40

45

50

55

60

0 5 10 15 20 25 30 35

Coh

esio

n (c

) kP

a

% RHA

7 Days 14 Days

28 Days 56 Days

128 Days

Figure 8. Cohesion of admixed soil.

from 28 to 56 kPa at 7 days and 128 days curing, respectively, for ash content between 0% and30%. Improvement on cohesion due to addition of RHA is slackened beyond 10% RHA content.Marked reduction in cohesion is observed beyond 30% RHA content (Figure 8). As in the case ofcohesion, a similar trend of improvement is observed for the internal friction angle. However, themaximum improvement rate is observed upto 5% RHA beyond which the improvement on theinternal friction angle is mild upto 15% RHA content in comparison to the improvement observedat 5% RHA content (Figure 9). But overall, the maximum internal friction angle is observedbetween 20% and 30% RHA content (Figure 9). This significant alteration in soil property is most

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8

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22

24

26

28

0 5 10 15 20 25 30 35

Ang

le o

f in

tern

al f

rict

ion

(j)

º

% RHA

7 Days 14 Days

28 Days 56 Days

128 Days

Figure 9. Angle of internal friction of admixed soil.

likely due to the presence of more clay particles in the soil mass, which ultimately lead to a bettermodification process in the presence of RHA.

4.6. Split tensile strengthNormally the compressive strength testing is used for the evaluationof strength of stabilised soilsand there are fewer studies concerning their tensile strength. Knowledge of the tensile strength isneeded in the study of stability of earth dams, highway and airfield pavements. Tensile stresses areset up due to movement of traffic on pavement, shrinkage of soils, seasonal variation in temperatureand alternate wetting and drying of soils, etc. Various tests and modifications have been developedand used for evaluating tensile strength of soils and stabilised soils. For conducting the split tensiletest, cylindrical specimens of size 50 mm diameter and 100 mm length were prepared at OMCand MDD in the same way as in the case of unconfined compression tests. The specimens wereplaced horizontally as shown in Figure 10 between the bearing blocks of the compression testingmachine. All tests were conducted at a constant axial strain at 1.25 mm/min after 7, 14, 28, 56 and128 days curing periods to obtain failure load. The results of split tensile strength are presented inFigure 10 for various soil-RHA mixtures. The split tensile strength is obtained by the followingequation:

Split tensile strength(σt) = 2PπLD

,

where P is the failure load; L the length of specimen and D the diameter of the specimen.Adding of RHA to soil causes an increase split tensile strength. The trends of increase of split

tensile strength are depicted in Figure 11. From the present laboratory study, it is seen that gainof split tensile strength is very significant up to 15% RHA content beyond which this rate ofgain slows down. Maximum split tensile strength was offered by the soil sample admixing 25%RHA irrespective of days of curing (Figure 11). The split tensile strength increased from 15.28 to22.89 kPa for a 7-day curing period and from 15.28 to 24.34 kPa for 128 days curing period withrespect to virgin soil when ash content increased from 0% to 25%. Beyond 25% RHA content, thesplit tensile strength decreases considerably. It is seen that prolonged curing has a lot of impactas far as split tensile strength improvement is concerned.

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Road Materials and Pavement Design 549

Figure 10. Testing setup for splitting tensile strength.Source: The author.

15

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0 5 10 15 20 25 30 35

Split

ten

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h (s

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Figure 11. Split tensile strength of admixed soil.

4.7. Ratio of split tensile strength and unconfined compressive strengthFigure 12 shows the influence of RHA content on the ratio of split tensile strength and UCS. Theresults show that UCS and split tensile strengths are closely related. It can be observed that theratio of split tensile strength and UCS decreased with increase in RHA content, indicating thatRHA is more efficient when soil was subjected to compression rather than to tension.

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0.12

0.13

0.14

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0.16

0.17

0.18

0.19

0 5 10 15 20 25 30 35

Rat

io (

s t/qu)

% RHA

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56 Days 128 Days

Figure 12. Split tensile strength/UCS ratio of admixed soil.

The relative relationship and mobilisation between the tensile strength and compressive strengthcould be discussed by plotting the tensile/compressive strength ratio (σt/qu) versus differentpercentage values of RHA. The ratio (σt/qu) decreases up to 5% RHA content and thereafter therate of decrease in ratio is steady. The decrease in ratio (σt/qu) is not much affected by prolongedcuring as depicted in the Figure 12.

5. Cyclic triaxial testRepeated triaxial tests were conducted on a sample of size 100 mm diameter and 200 mm heightin conventional triaxial cell by static compaction at OMC. The frequency of load application inall were tested and kept at 70 cycle/min; this was fixed based on traffic density (Kumar & Singh,2008). The loads were applied up to 10,000 cycles and behaviour of resilient strain was observedat different cycles by a computerised data logger system. In the present study, the cyclic triaxialtests were conducted as per ASTM D5311-11 on natural and treated stabilised specimens. Thestress–strength ratio in this study called as deviator stress levels (DSLs) can be defined as theratio of the σd of repeated load triaxial test to the soil strength obtained from undrained triaxial(σs). The average response of total resilient strain (εr) under each deviator stress level (σd ) forthe last five cycles of the testing phase was measured to determine the resilient modulus (MR) byusing the following equation:

MR = σd

εr

For the analysis of resilient modulus (MR) results, a set of six tests was conducted on bothexpansive and RHA admixed soils. Tests were conducted at two pre-determined DSL, i.e. 0.5 and0.8 DSL. Similarly, three confining pressures of 100 kPa, 150 kPa and 200 kPa were chosen for thetest. Throughout the test, the aforementioned DSL rates and confining pressures were maintained.The main objective of this study was to understand the effects of the confining pressure and DSLon the expansive soil and FA admixed soils.

Figure 13 explains that the increase in the confining pressure resulted in enhancements of MR

of all cases, but these values diminished at higher DSL values. MR values increase with increasein RHA content irrespective of DSL and confining pressure. The maximum MR values observedwere 110 and 69 MPa at 0.5 and 0.8 DSL, respectively, for a constant 200 kPa confining pressurewhen no admixing was done. But these values increased to 214 and 134 MPa, respectively, afteradmixing of 25% RHA. This effect may be attributed to a stiffer soil skeleton structure of RHA

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Road Materials and Pavement Design 551

0

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Res

ilien

t m

odul

us (

MR

) M

Pa

CP 100CP 150CP 200

Figure 13. Resilient modulus of admixed soil.

admixed soils caused by increased confinement and pozzolanic reactions, which results in a closerbonding of soil particles.

6. Cost analysisThe admixing of optimum content of RHA increased the value of CBR from 2% to 10.5%. Theincrease in CBR value shows the thickness reduction in different layers as resulting in the costreduction of pavement. According to CBR values of natural soil and soil admixed with optimumcontent of additives, the total thickness of pavement excluding subgrade was determined as perIRC: 37-2012. The total thickness of pavement was 805 mm in the case of natural subgrade soiland the value was reduced and became 600 mm after admixing of RHA. As per the schedulerates of 2012, the Government of Uttar Pradesh, India, the cost of stabilised and unstabilised soilsubgrade pavement per km per lane of pavement for cumulative traffic of 50 msa in Indian Rupeeshas been calculated. The total cost of pavement was 136.08 lakh/km/lane when subgrade soilwas natural soil, but it reduced to 104.95 lakh/km/lane by admixing 25% RHA subgrade soil.The total cost saving was 22.88% after admixing of RHA.

7. ConclusionsThe following conclusions have been drawn from the present laboratory study:

• Admixing of RHA improves shrinkage limits considerably and the improvement was morepronounced for 30% RHA.

• Inclusion of RHA to clayey soil reduces the dry density. The reduction in dry density isalmost linear with RHA content. But it demands higher water content.

• Admixing of RHA upto 25% could accelerate soaked CBR value upto 10.5% from 2% ofclayey soil at 7 days curing. As far as soaked CBR value improvement is concerned, RHAproduced higher CBR value upto 13.6% at 25% RHA content for a curing period of 128days.

• Significant improvements on UCS and split tensile strength were observed for RHAadmixed soil samples up to 25% after which the rate of improvement gradually slackened.However, UCS of RHA admixed soil samples are higher than 100% clayey soil sampleirrespective of the curing period. The ratio (σt/qu) decreases up to 5% RHA content andthereafter the rate of decrease slackens. The decrease in ratio (σt/qu) is not much affected

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552 A.K. Anupam et al.

by prolonged curing. The decrease in ratio (σt/qu) indicates that RHA is more efficientwhen soil is subjected to compression rather than to tension. Admixing of RHA shows apositive influence on cohesion and internal friction angle considerably.

• Resilient modulus (MR) values increase with increase in additives content irrespective ofDSL and confining pressure. The maximum MR values observed were 110 and 69 MPa at0.5 and 0.8 DSL, respectively, for a constant 200 kPa confining pressure when no admixingwas done. These values increased to 214 and 134 MPa after admixing 25% RHA for thesame working condition. Improvement in resilient modulus of expansive soil on admixingof additives may be due to a stiffer soil skeleton structure of RHA caused by increasedconfinement and pozzolanic reactions, which result in a closer bonding of soil particles.

• Admixing of optimum content of RHA is a cost saving of about 22.88%. Based on thepresent study, authors opined that RHA can be utilised as an effective soil stabiliser for roadconstruction if found abundantly.

ReferencesAlhassan, M. (2008). Potentials of rice husk ash for soil stabilization. Assumption University Journal of

Technology, 11(4), 246–250.Ali, M., & Sreenivasulu, V. (2004). An experimental study on the influence of rice husk ash and lime on

properties of bentonite. Proceedings of Indian geotechnical conference,Warangal (India), 468– 471.Basha, E. A., Hashim, R., Mahmud, H. B., & Muntohar, A. S. (2005). Stabilization of residual soil with

rice husk ash and cement stabilization of residual soil with rice husk ash and cement. Construction andBuilding Materials, 19, 448–453.

Behak, L., & Nunez, W. P. (2013). Effect of burning temperature on alkaline reactivity of rice husk ash withlime. Road Materials and Pavement Design, 14(3), 570–585.

Brooks R. M. (2009). Soil stabilization with fly ash and rice husk ash. International Journal of Researchand Reviews in Applied Sciences, 1(3), 209–217.

Camargo, F. F., Edil, T. B., & Benson, C. H. (2013). Strength and stiffness of recycled materials stabilisedwith fly ash: A laboratory study. Road Materials and Pavement Design, 14(3), 504–517.

Chandra, S., Kumar, S., & Anand, R. K. (2005). Soil stabilization with rice husk ash and lime sludge. IndianHighways, 33(5), 87–98.

Choobbasti, A. J., Ghodrat, H., Vahdatirad, M. J., Firouzian, S., Barari, A., Torabi, M., & Bagherian, A.(2010). Influence of using rice husk ash in soil stabilization method with lime. Frontiers of Earth Sciencein China, 4(4), 471–480.

Dimter, S., Rukavina, T., & Drag, V. (2011). Strength properties of fly ash stabilized mixes. Road Materialsand Pavement Design, 12(3), 687–697.

El-Aziz, M. A. A., & Abo-Hashema, M. A. (2013). Measured effects on engineering properties of clayeysubgrade using lime–Homra stabilizer. International Journal of Pavement Engineering. 14(4), 321–332.

Govindarao, V. M. H. (1980). Utilization of rice husk – a preliminary analysis. Journal of Science andIndustrial Research, 39(6), 495–515.

Jha, J. N., & Gill, K. S. (2006). Effect of rice husk ash on lime stabilization. Journal of the Institution ofEngineers (India), 87, 33–39.

Kumar, P., & Singh, S. P. (2008). Fiber-reinforced fly ash subbases in rural roads. Journal of TransportationEngineering, ASCE, 134(4), 171–180.

Mantohar, A. S., & Hantoro, G. (1999). Behavior of engineering properties on the clay blended withLRHA (lime rice husk ash). Research Report for Grant 1999 Muhammadiyah University of Yogyakarta,Indonesia.

Muntohar, A. S. (2002). Utilization of uncontrolled burnt rice husk ash in soil improvement. Dimensi TeknikSipil, 4(2), 100–105.

Muntohar, A. S. (2011). Effect of specimen size on the tensile strength behavior of the plastic waste fiberreinforced soil – lime – rice husk ash mixtures. Civil Engineering Dimension, 13(2), 82–89.

Noor, M. J. M. M., Aziz, A. A., & Suhadi, R. U. R. (1993). Effect of cement-rice husk ash on compaction,strength and durability of Melaka series of lateritic soil. The Professional Journal of the Institution ofSurveyors Malaysia, 28(3), 61–67.

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Olawale, O., & Oyawale, F. A. (2012). Characterization of rice husk via atomic absorption spectrophotometerfor optimal silica production. International Journal of Science and Technology, 2(4), 210–213.

Seco, A., Ramirez, F., Miqueleiz, L., & Garcia, B. (2011). Stabilization of expansive soils for use inconstruction. Applied Clay Science, 51, 348–352.

Yadu, L., Singh, D., & Tripathi, R. K. (2011). Strength characteristics of rice husk ash stabilized black cottonsoil. Proceedings of international conference on Advances in Materials and Techniques for InfrastructureDevelopment (AMTID 2011), NIT Calicut, India, 1–6.

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