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Static and cyclic properties of clay subgrade stabilisedwith rice husk ash and Portland slag cementArgaw Asha Ashangoa & Nihar Ranjan Patraa

a Geotechnical Engineering Division, Department of Civil Engineering, IIT Kanpur, Kanpur208016, IndiaPublished online: 07 Mar 2014.

To cite this article: Argaw Asha Ashango & Nihar Ranjan Patra (2014) Static and cyclic properties of clay subgradestabilised with rice husk ash and Portland slag cement, International Journal of Pavement Engineering, 15:10, 906-916, DOI:10.1080/10298436.2014.893323

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Static and cyclic properties of clay subgrade stabilised with rice husk ashand Portland slag cement

Argaw Asha Ashango1 and Nihar Ranjan Patra*

Geotechnical Engineering Division, Department of Civil Engineering, IIT Kanpur, Kanpur 208016, India

(Received 3 July 2013; accepted 19 January 2014)

In the present study, clay soil collected from new Banda, Uttar Pradesh, India has been treated with rice husk ash (RHA)and Portland slag cement (PSC). Based on unconfined compressive strength test results, the optimum mix obtained is of82.5%Soil þ 7.5%PSC þ 10%RHA. The increase in strength of the optimum mix is about 29.8%, 37.2% and 48.55%for a curing period of 7, 14 and 30 days, respectively. The soaked California bearing ratio (CBR) test gives about91.75% higher values as compared to unsoaked CBR test for a curing period of 30 days. Strain-controlled cyclictriaxial tests were conducted to study the variation of degradation index, shear modulus and damping ratio of theoptimum mix with number of cycles for strain amplitudes of 0.4%, 0.6%, 0.8% and 1% and for frequencies of 0.2 and1Hz at an effective confining pressure of 100 kPa. It is observed that the degradation index decreases at a fast rate forthe first 25–50 cycles. From the study, it is concluded that the aforementioned mix may be suitable for pavementsubgrade material.

Keywords: clay subgrade; rice husk ash; Portland slag cement; California bearing ratio; cyclic tests; degradation index

List of notations

AASHTO: American Association of State Highway and

Transportation Officials

ASTM: American Society for Testing and Materials

ASTM D: American Society for Testing and Materials

Designation

CAH: calcium aluminates hydrate

CBR: California bearing ratio

CH: highly expansive clay soil

CSH: calcium silicate hydrate

D: damping ratio

G: shear modulus

Hz: Hertz

IS: Indian Standard

JCPDs: Joint Committee on Powder Diffraction

Standards

MDD: maximum dry density

OMC: optimum moisture content

PSC: Portland slag cement

RHA: rice husk ash

UCS: unconfined compressive strength

UCSC: Unified Soil Classification System

XRD: X-ray diffraction

XRF: X-ray fluorescence

d: degradation index

g: strain amplitude

1. Introduction

Expansive soils are found in the arid and semi-arid regions

and formed due to poor drainage and hot climatic

condition, and its colour varies from grey to deep black

and rarely reddish or yellowish and the thickness also

varies from 30 cm to 15m (Rao 2000). Twenty percent of

the total land in India is covered by expansive soils and

generally it is called black cotton soil (Rao 2000). In

addition to India, this black cotton soil is available in many

parts of the world such as Africa, Australia, Ethiopia,

Israel, Jordan, the USA, and so on (Rao 2000). The annual

damage to civil engineering structure due to this soil are

estimated to be around billion dollars in the world and

particularly 1 billion dollars in the USA and 150 million

dollars in the UK (Gourley et al. 1993, Sabat and

Nanda 2011).

Rice husk ash (RHA) is a waste material obtained from

controlled burning of rice husks at a temperature of 6008C(Della et al. 2002) and 20% of rice husk are ash. RHA is

classified as a pozzolanic material [American Society for

Testing Materials (ASTM) C618 2012a], which is

siliceous and aluminous by composition. This material is

in bulk amount in major rice producing countries such as

India and China (Ramakrishna and Pradeep 2008) and its

fineness and low density make it to fly over the air, which

contributes to environmental issues and in addition to that

storage has claimed for land proclamation (Rahman 1987).

q 2014 Taylor & Francis

*Corresponding author. Email: nrpatra@iitk.ac.in

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Portland slag cement (PSC) is made by inter-grinding

of high quality of clinker, slag and gypsum. Clinker used

for the production of slag cement contains highly reactive

tri-calcium silicates (3CaO·SiO2) that facilitate good

reactivity and strength development in the cement.

Granulated blast furnace slag containing high glass

content (more than 90%) is obtained by rapid quenching

or chilling of molten slag generated from blast furnace

during steel making. Gypsum (CaSO4·H2O) is added to the

clinker and slag to manufacture PSC and it should be in

amounts such that the sulphur trioxide (SO3) in the cement

produced does not exceed the limit of 3%. It is a

cementitious material consisting of lime (CaO), silicon

dioxide (SiO2), aluminum oxide (Al2O3) and magnesium

oxide (MgO). The high amount of lime(CaO), 50.85%,

present in PSC makes it a suitable binding material for

mixing it with silicon dioxide (SiO2) that exist in RHA.

The PSC does not contain carbon and it does not cause

instability in the entrained air content.

Aubert et al. (2006) have reported that reusing thewaste

material in environmentally friendly and economically

sustainable ways are important topics on which authorities

and researchers are working on. Apart from this, the

demand of construction material and its cost increases day

by day and this leads to scarcity of raw materials and

increase in price of energy. The improvement in strength of

the clay soil is due to the presence of cementitiousmaterials

in soil–cement matrix (Stavridakis 2005, Kamruzzamn

et al. 2006). The cementitious materials are formed by the

reaction between hydrated lime from cement and the silica

and alumina from RHA and clay minerals and that leads to

formation of calcium silicate hydrate and calcium

aluminates hydrate (Rahman et al. 2010).

The heavy traffic loading, railway, earthquake, etc. can

affect the dynamic property of soils (Thammathiwat and

Chim-oye 2004). This dynamic property of soils such as

shear modulus and damping ratio depends on the cyclic

frequency and strain amplitude (Zhou and Gong 2001,

Jiang et al. 2010). The cyclic loading affects the

chemically mixed soils (Hoyos et al. 2004, Shafiee et al.

2004). Few cyclic triaxial test results of stabilised clay soil

have been reported by Ashango and Patra (2013). Clay soil

stabilised with RHA and PSC in terms of strength,

durability and California bearing ratio (CBR) are limited.

In the present study, black cotton clay soil collected

from new Banda, Uttar Pradesh, India has been mixed with

RHA and PSC to determine the optimum mix. The

unconfined compressive strength (UCS) of the optimum

mix has been carried out for different curing periods. The

unsoaked and soaked CBR tests have been carried out for

the mixture for different curing periods. The durability test

is carried out for the optimummix. Strain-controlled cyclic

triaxial tests have been conducted to study the variation of

degradation index, d, shear modulus, G and damping ratio,

D of the optimum mix of soil with number of cycles for

different strain amplitudes of 0.4%, 0.6%, 0.8% and 1%and

effective confining pressure of 100 kPa at a frequency of 0.2

and 1Hz. Based on static and cyclic test results on stabilised

clay, conclusions have been drawn for the material mix and

its applicability for pavement subgrade.

2. Experimental programme

The experimental programme was divided into four parts.

In the first part, the geotechnical properties of the soil, RHA

and PSC were determined. In the second part, the optimum

mix for stabilisation of the soil sample was determined. In

the third part, unsoaked and soaked CBR tests, unconfined

compression test and durability testswere carried out. In the

fourth part, cyclic tests have been conducted to determine

degradation index, shear modulus and damping ratio of the

optimummix. The detailed experimental programme of the

present study is given in Table 1.

3. Materials

The three materials are used in this study and explained in

detail in the next section. The samples of each material are

shown in Figure 1.

3.1 Soil sample

The soil (black cotton) used in the present study was

collected from new Banda site, Uttar Pradesh, India. The

geotechnical properties of the soil are shown in Table 2,

and the particle size distribution is shown in Figure 2. The

soil was classified as highly expansive soil according to

Unified Soil Classification System and A-7-6 according to

American Association of State Highway and Transpor-

tation Officials (AASHTO) classification system. The soil

has approximately 98% particles passing U.S. No 200

sieve. The silt and clay fractions are about 52% and 46%,

respectively.

3.2 Rice husk ash

Rice husk is milled at circulating fluidised bed boiler at

4708C temperature and Lancashire boiler at 6708C and

collected from locally available resources. The chemical

analysis has shown that the RHA consists of 81.9% SiO2,

0.9% Al2O3, 0.4% Fe2O3, 0.8% CaO, 0.5% MgO,0.4%

Na2O, 1.3% K2O, 0.1% MnO2, 4% C and 4% loss of

ignition. The physical properties of RHA are shown in

Table 3.

3.3 Portland slag cement

The PSC was collected from the locally available market

(Gujarat, India). PSC is made by inter-grinding of high

quality clinker, slag and gypsum. It is a cementitious

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Figure 1. Clay soil, PSC and RHA used in present study.

Table 2. Geotechnical properties of the clay soil and optimum(82.5%Soil þ 7.5%PSC þ 10%RHA) mix.

Values

Soil properties Clay Optimum mix

Grain size distributionGravel (.4.75mm) 0 0Sand (4.75 to 0.075mm) 2 0.7Silt (0.075 to 0.002mm) 52 98.05Clay (,0.002mm) 46 1.25Specific gravity 2.69 2.47

Atterberg limitLiquid limit (%) 53 51.5Plastic limit (%) 20 41.28Plasticity index (%) 33 10.22Shrinkage limit (%) 11 46.32

Proctor compactionMDD (kN/m3) 16.12 14.79OMC (%) 22 25.25Compressive strength (kN/m2) 193 835

CBR (%)Unsoaked 8.27 15.8 Figure 2. Particle size distribution of the clay soil and optimum

mix (82.5%Soil þ 7.5%PSC þ 10%RHA).

Table 1. Testing scheme and mixture design.

Materials used Static Test Cyclic test

CBR Frequency

UCS Unsoaked Soaked Durability 0.2Hz 1Hz

Mix proportion (%) Curing days Uncuried Curing days D/W days Strain amplitude (%) Strain amplitude (%)

Clay PSC RHA 0 7 14 30 0 7 14 30 30 0.4 0.6 0.8 1 0.4 0.6 0.8 1

100 0 0 X X90 0 10 X X X X X X X X92.5 2.5 5 X87.5 2.5 10 X X X X X82.5 2.5 15 X77.5 2.5 20 X90 5 5 X85 5 10 X X X X X X80 5 15 X75 5 20 X87.5 7.5 5 X82.5 7.5 10 X X X X X X X X X X X X X X X X X77.5 7.5 15 X72.5 7.5 20 X

Note: X, test conducted; D/W, drying and wetting.

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material that consists of lime (CaO), silicon dioxide

(SiO2), aluminum oxide (Al2O3) and magnesium oxide

(MgO). X-ray fluorescence was carried out by ZFX Primus

II RIGAKU machine with 36.58C internal temperature and

3 kV power for the PSC to find the oxide contents. The

chemical analysis shows that the PSC consists of 50.8%

CaO, 27.7% SiO2, 11.2% Al2O3, 2.9% Fe2O3, 2.8% SO3,

2.5% MgO, 0.6% Na2O and 0.5% K2O. The high amount

of lime (CaO) in PSC reflects it as a binder material.

4. Testing procedures

4.1 Static tests

The geotechnical laboratory tests were carried out on clay

soil for the classification of the expansive soil. The RHA

varies from 5% to 20% with increment of 5% and the PSC

varies from 2.5% to 7.5% with increment of 2.5% of dry

unit soil which were mixed thoroughly and kept for

10min. The maximum dry density (MDD) and the

optimum moisture content (OMC) for various mixtures

were determined by standard proctor method in accord-

ance with ASTM 698. UCS test was conducted on sample

having a dimension of 38mm diameter and 76mm height

prepared with their respective mix of MDD and OMC in

accordance with ASTM 2166 for three samples. The

average of them was taken as the UCS value. This sample

was tested after 0, 7, 14 and 30 days of curing in a room

maintained at 90–100% relative humidity and temperature

of 32–358C with a strain rate 0.625mm/min.

Test specimens were prepared at OMC with their

respective mix for CBR test in accordance with ASTM

1883. The CBR tests were conducted for unsoaked and

soaked conditions. The sample was soaked for 4 days after

cured in a room maintained at 90–100% relative humidity

and temperature of 32–358C for 0, 7, 14 and 30 days.

Then, the sample was tested at a strain rate of 1.25mm/

min. The durability test was conducted for three samples

prepared for UCS tests in two steps: wetting and drying.

In the wetting case, the samples after 7 days of curing were

immersed in water for 5 h. Then, their weight and height

were recorded. In the drying case, the samples were dried

after 5 h of immersion in water. Then, their weight and

height were measured. These samples were oven-dried for

42 h at a temperature of 808C and were cooled for 1 h.

Then their weight and height were measured. This

completes the wetting and drying for one cycle. The

same procedure was repeated for 12 cycles. The sample

that existed for 12 cycles was tested for UCS test in

accordance with ASTM 559.

4.2 X-ray diffraction analysis

X-ray diffraction (XRD) analysis was carried out for clay

soil, RHA, optimum mix after static test and optimum mix

after cyclic test using SIETRONICS XRD SCAN

instrument. XRD patterns were obtained using a Cu, Ka(l ¼ 1.541841 A) with continuous scan mode over a range

of 5–7082u with a 0.028 step and a 2 s per step count time.

The analysis was performed by comparing or matching the

Joint Committee on Powder Diffraction Standards data

and the scanned XRD data for different minerals such as

montmorillonite, kaolinite, illite, quartz, feldspar and

calcite. The minerals contents in samples of clay soil,

RHA, optimum mix after static test and optimum mix after

cyclic test are shown in Figures 3–6, respectively.

4.3 Cyclic tests

The optimum mix samples (Soil-PSC-RHA) were

prepared having 50mm diameter and 100mm height

mould and compacted with 98% of MDD. Strain-

controlled cyclic triaxial test was conducted in accordance

with ASTM 3999 up to 300 number of cycles with

different strain amplitudes of g ¼ 0.4%, 0.6%, 0.8% and

1%, frequency of 0.2 and 1Hz at an effective confine

pressure of 100 kPa.

5. Test results and discussions

5.1 XRD analysis

The XRD analyses are shown in Figures 3–6 for clay soil,

RHA, optimum mix after static test and optimum mix

Table 3. Physical properties of RHA.

Property Value

Colour Black greyBulk density 3.2 kN/m3

Moisture 1.6%Specific gravity 2.308PH 8.4

Figure 3. XRD of clay soil sample. 1, illite (Al2Si3(OH)2); 2,kaolinite (Al2Si2O5 (OH)4); 3,montmorillonite (Al2O34SiO2·H2O);4, quartz; 5, calcite (CaCO3).

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after cyclic test, respectively. The clay soil sample has

the broad smooth hump between 26.782u and 26.882uwhich indicates that the soil has major montmorillonite

(Al2O34SiO2·H2O) mineral. The broad smooth hump for

RHA is between 33.1582u and 33.2582u and shifts to the

right side compared to clay soil and the optimum mix. Its

intensity is less than the soil and greater than the optimum

mix after cyclic test as shown in Figure 4. The optimum

mix after static test has the broad smooth hump between

25.7582u and 25.8582u which indicates that the optimum

mix has major illite (Al2Si3(OH)2) mineral (Figure 5). The

optimum mix after cyclic test has the broad smooth hump

between 25.7582u and 25.8582u (Figure 6). The intensity isreduced almost by half from static to cyclic test case for

the optimum mix.

5.2 Moisture–density relationship

Moisture–density relationships of stabilised clay soil

obtained from standard proctor tests are plotted for the

RHA and PSC mix containing 0%, 5%, 10%, 15% and

20% of RHA and 2.5%, 5% and 7.5% of PSC (Figures 7

and 8). The result shows that the OMC of stabilised soil

increases with increase in RHA. The MDD of stabilised

soil decreases with increase in RHA. The MDD and OMC

for clay soil are 16.12 kN/m3 and 22%, respectively. The

MDD and OMC for the optimum mix are 14.79 kN/m3 and

25.25%, respectively. The optimum mix is determined

from the UCS test results which are discussed in the next

section. The OMC increases from 22% to 25.25% and the

MDD decreases from 16.1 to 14.79 kN/m3 from virgin soil

to stabilised clay soil. The increase in OMC (from 22% to

25.25%) is observed at 10%RHA, 7.5% of PSC and 82.5%Figure 5. XRD of optimum mix (82.5%Soil þ 7.5%PSC þ 10%RHA) sample after static triaxial test. 1, illite(Al2Si3(OH)2); 2, kaolinite (Al2Si2O5 (OH)4); 3, montmorillonite(Al2O34SiO2·H2O); 4, quartz; 5, calcite (CaCO3).

Figure 7. Variation of MDD with RHA for soil stabilized withPSC.

Figure 4. XRD of RHA sample. 1, montorillonite(Al2O34SiO2·H2O); 2, kaolinite (Al2Si2O5(OH)4); 3, illite(Al2Si3(OH)2); 4, quartz; 5, calcite (CaCO3).

Figure 6. XRD of optimum mix (82.5%Soil þ 7.5%PSC þ 10%RHA) sample after cyclic triaxial test. 1, illite(Al2Si3 (OH)2); 2, kaolinite (Al2Si2O5 (OH)4); 3, montmorillonite(Al2O34SiO2·H2O); 4, quartz; 5, calcite (CaCO3).

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of soil. This may be due to the absorption of excess water

by RHA (Ali et al. 1992). The relatively lower specific

gravity of RHA compared to clay soil (Ali et al. 1992) and

PSC may be attributed to the replacement of soil by this

material which results in decrease in MDD. Both RHA and

PSC reduce the dry density. The dry density reduces

because of change in particle size and specific gravity of

the soil, RHA and Portland cement (Rahman 1987). The

decrease in dry density leads to low compactive energy,

and the cost of compaction becomes economical for soils

compacted at low compactive energy (Basha et al. 2005,

Muntohar 2006).

5.3 Unconfined compression tests

The effectiveness of stabilisation method for a given

material is most popularly evaluated by the UCS test

(Lambe 1958, Katti et al. 1966, Swaminathan 1976,

Rahman 1987). The strength of stabilised material

increases with increase in PSC as shown in Figure 9.

The optimum mix is the mix having highest UCS values

for the given condition and which is found to be 82.5%

Soil þ 7.5%PSC þ 10%RHA. For clay soil, the UCS

value is 193 kN/m2 and this value increased to 458 kN/m2

for 5% increase in RHA and 2.5% increase in PSC which

is about 57.8% higher. Also, the strength increases from

193 to 835 kN/m2 for 10% increase in RHA and 7.5%

increase in PSC in the mix which is 76.8% higher. The

strength of treated soil is greater than untreated soil.

Generally, the result shows that the strength of the mix is

increased up to 10% of RHA for different mixtures of PSC.

For different curing periods, the strength of the stabilised

soil increases with increase in curing periods as shown in

Figure 10. The UCS value of the stabilised mix increases

from 458 to 582 kN/m2 for the 7-day curing period for

2.5% of PSC and 2.5%RHA which is 21.3% increase.

Typically, for 82.5%Soil þ 7.5%PSC þ 10%RHA mix,

the UCS value increases from 835 to 1190 kN/m2, 1330

and 1623 kN/m2 for 7, 14 and 30 days of curing periods,

respectively. The increase in strength in percent for this

mix is 29.83%, 37.2% and 48.55% for 7, 14 and 30 days of

curing periods, respectively. The increase in compressive

strength is due to frictional resistance from RHA and

cohesion from the expansive soil (Hossain 2011, Sabat and

Nanda 2011). The stress–strain curve for UCS tests for the

optimum mix at different curing periods is shown in

Figure 11. The failure strain is about 3.5% for 0 curing day

and 5% for 7, 14 and 30 curing days for the optimum mix.

5.4 CBR tests

The CBR test is a simple strength test that compares the

bearing capacity of a material with that of a well-graded

crushed stone (thus, a high quality crushed stone material

Figure 8. Variation of OMC with RHA for stabilized soil withPSC.

Figure 9. Variation of compressive strength with RHA forstabilized soil with PSC.

Figure 10. Variation of compressive strength with curing daysfor stabilized soil with PSC and RHA.

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should have a CBR @ 100%) (AASHTO 2000). The CBR

tests were carried out on stabilised soil for different mix

proportions on unsoaked and soaked conditions. The

unsoaked CBR value increases from 8.27% to 15.8% with

increase in RHA up to 10% and PSC up to 7.5%. At 10%

RHA, the soakedCBR value increases with increase in PSC

from 2.5%, 5% and 7.5% to 9.35%, 12.6% and 14.8%,

respectively as shown in Figure 12. The curing effect was

studied for 7, 14 and 30 days. Four days soaking in water

were carried out for 90%Soil þ 10%RHA mixture sample

and 82.5%Soil þ 7.5%PSC þ 10%RHA mixture sample

after 7, 14 and 30 days of curing. The result of CBR test

shows that the CBR value increases from 14.8% to 19.59%

for the curing periods 7–30 dayswhich is 24.5% increase as

shown in Figure 13. The increase in CBR value shows that

the stabilised material quality is good enough for subgrade

material. The increase in CBR is due to the cementing

property of PSC and the pozzolanic property of RHA.

5.5 Durability tests

Durability tests were conducted in accordance with ASTM

D559 for 90%Soil þ 10%RHA sample mixture and 82.5%

Soil þ 7.5%PSC þ 10%RHA sample mixture. The 90%

Soil þ 10%RHA mix demolished after the 5th cycles due

to lack of any binder. However, 82.5%Soil þ 7.5%

PSC þ 10%RHA sample survived for 12 wet–dry cycles

due to the PSC binder and the UCS test was carried out to

determine the strength of the material. The result of

durability (Ri ¼ soaked UCS/unsoaked UCS) for soil

stabilised with PSC shows that Ri ¼ 0.91. Overall, the soil

stabilised with 7.5%PSC showed better durability than

untreated clay soil.

5.6 Cyclic test results

The variations of deviator stress with axial strain of

optimum mix (82.5%Soil þ 7.5%PSC þ 10%RHA)

sample have been plotted for different frequencies and

different strain amplitudes up to 300 cycles. Typical

diagrams for strain amplitude of 0.4% at 0.2 Hz is shown

in Figure 14. The deviatoric stress decreases with increase

in the number of cycles. The variations of excess pore

pressure with time of the optimum mix (82.5%

Soil þ 7.5%PSC þ 10%RHA) sample have been plotted

for different frequencies and different strain amplitudes up

to 300 cycles. Typical diagrams for strain amplitude of

0.4% at 0.2Hz is shown in Figure 15. The excess pore

water pressure developed slowly and finally it reaches to

70% for 300 cycles. The variations of deviatoric stress

with mean normal effective stress of optimum mix (82.5%

Soil þ 7.5%PSC þ 10%RHA) sample have been plotted

for different frequencies and different strain amplitudes up

to 300 cycles. Typical diagrams for strain amplitude of

0.4% at 0.2 and 1Hz are shown in Figures 16 and 17. The

mean effective stress is greater on the extension side and

Figure 11. Typical stress strain diagram for optimum mix atdifferent curing periods.

Figure 12. Variation of soaked CBR with PSC for stabilizedsoil.

Figure 13. Variation of soaked CBR with curing days forstabilized soil with RHA and PSC.

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the compression side for 0.2 and 1 Hz frequency,

respectively.

The variations of shear modulus with numbers of

cycles of the optimum mix (82.5%Soil þ 7.5%

PSC þ 10%RHA) sample have been plotted for different

frequencies and different strain amplitudes. Typical

diagrams for strain amplitude of 0.4%, 0.6%, 0.8% and

1% at 0.2 and 1Hz are shown in Figures 18 and 19,

respectively. The shear modulus decreases with increase in

strain amplitude. The shear modulus gradually decreases

up to 100 cycles and continually with decreasing slope up

to 300 cycles. The shear modulus decreases from 11,505 to

5870 kPa, 10,742 to 5088 kPa, 9255 to 3472 kPa and 9173

to 3155 kPa with increase in number of cycle at strain

amplitudes of 0.4%, 0.6%, 0.8% and 1%, respectively at

0.2 Hz frequency and it decreases from 14,565 to

3770 kPa, 7598 to 2252 kPa and 6492 to 1549 kPa with

increase in number of cycles at strain amplitudes of 0.4%,

0.8% and 1%, respectively, at 1Hz frequency.

Figure 14. Variation of deviatoric stress with axial strain foroptimum mix (0.2Hz).

Figure 15. Variation of excess pore water pressure with time foroptimum mix (0.2Hz).

Figure 16. Variation of deviatoric stress with mean normaleffective stress for optimum mix (0.2Hz).

Figure 17. Variation of deviatoric stress with mean normaleffective stress for optimum mix (1Hz).

Figure 18. Variation of shear modulus with number of cyclesfor optimum mix (0.2Hz).

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The variations of damping ratio with number of cycles

of the optimummix (82.5%Soil þ 7.5%PSC þ 10%RHA)

sample have been plotted for different frequencies and

different strain amplitudes. Typical diagrams for strain

amplitude of 0.4%, 0.6%, 0.8% and 1% at 0.2 and 1Hz are

shown in Figures 20 and 21, respectively. The damping

ratio increases with increase in strain amplitude from 0.4%

to 1%. The damping ratio decreases from 12.7% to 9.1%,

14.75% to 11%, 17.8% to 13% and 19.5% to 14.9% with

increase in the number of cycles at strain amplitudes of

0.4%, 0.6%, 0.8% and 1%, respectively, at a frequency of

0.2Hz. In the same way, at a frequency of 1Hz the

damping ratio decreases from 19.8% to 16.54%, 21% to

17.5% and 24% to 19.6% with increase in number of cycle

at strain amplitudes of 0.4%, 0.8% and 1%, respectively.

The variations of degradation index with number of

cycles of optimum mix (82.5%Soil þ 7.5%PSC þ 10%

RHA) sample have been plotted for different strain

amplitudes at a frequency of 0.2 and 1Hz and are shown in

Figures 22 and 23. Idriss et al. (1978) reported that the

degradation index, d, can be determined from the ratio of

Figure 19. Variation of shear modulus with number of cyclesfor optimum mix (1Hz).

Figure 21. Variation of damping ratio with number of cycles foroptimum mix (1Hz).

Figure 20. Variation of damping ratio with number of cycles foroptimum mix (0.2Hz).

Figure 22. Variation of degradation index with number ofcycles for optimum mix (0.2Hz).

Figure 23. Variation of degradation index with number ofcycles for optimum mix (1Hz).

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secant modulus in the Nth cycle to secant modulus in the

first cycle.

The degradation index decreases at a fast rate for first

25–50 cycles and then it is almost constant or the decrease

is negligible. The degradation index decreases from 1% to

0.51%, 1% to 0.47%, 1% to 0.37% and 1% to 0.34% with

increase in the number of cycle at strain amplitudes of

0.4%, 0.6%, 0.8% and 1%, respectively, at a frequency of

0.2Hz. In the same way, the degradation index decreases

from 1% to 0.26%, 1% to 0.25% and 1% to 0.24% with

increase in the number of cycles at strain amplitudes of

0.4%, 0.8% and 1%, respectively, at a frequency of 1Hz.

The percentage decrease in degradation index is about

33% and 7.7% for strain amplitude varying from 0.4% to

1% at a frequency of 0.2 and 1Hz, respectively.

6. Conclusions

Based on the study, the following conclusions are drawn:

(1) The clay soil collected from new Banda, Uttar

Pradesh, India has been stabilised with RHA and

PSC. The percentage of soil, PSC and RHA that

gives the optimum mix is 82.5%, 7.5% and 10%,

respectively. The MDD decreases with increase in

PSC and RHA. However, the OMC increases with

increase in PSC and RHA in soil mixture. As a

general rule, the higher the compressive strength,

the better the quality of the stabilised material. The

compressive strength increases from 193 to

835 kN/m2 for the optimum mix and the percen-

tage increase is about 76.8%. For the optimum

mix, the increase in strength is about 29.83%,

37.2% and 48.55% for 7, 14 and 30 days of curing,

respectively. The failure strain is about 3.5%, for 0

curing day and 5% for 7, 14 and 30 curing days for

the optimum mix.

(2) The soaked CBR test results show that the CBR

value increases with increase in PSC and RHA for

the mix. About 91.75% increase in soaked CBR is

recorded for the optimum mix from virgin soil

which has 1.22% of CBR. After 12 wet–dry

cycles, the optimum mix survived and the

durability of the material is 0.91 to that of

unsoaked strength of the optimum mix.

(3) Strain-controlled cyclic triaxial tests have been

conducted to study the variation of degradation

index, d, shear modulus, G and damping ratio,

D of the optimum mix of soil with number of

cycles for different strain amplitudes of 0.4%,

0.6%, 0.8% and 1% and effective confining

pressure of 100 kPa at a frequency of 0.2 and

1Hz. The shear modulus decreases with increase

in the number of cycles and the damping ratio also

decreases with increase in the number of cycles.

The degradation index decreases at a fast rate for

first 25–50 cycles and then it is almost constant or

the decrease is negligible. The percentage

decrease in degradation index is about 33% for

strain amplitude varying from 0.4% to 1% at

0.2Hz frequency.

(4) Based on dry density, strength, durability and CBR

values, the stabilised subgrade material is suitable

for subgrade of flexible pavement.

Note

1. Email: argaw97@gmail.com

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