Stabilization of weak pavement subgrades using cement kiln dust 2

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),

ISSN 0976 – 6316(Online) Volume 4, Issue 1, January- February (2013), © IAEME

26

STABILIZATION OF WEAK PAVEMENT SUBGRADES USING

CEMENT KILN DUST

Brijesh Kumar1, Nitish Puri

2

1Assistant Professor, Department of Civil Engineering, HCTM Technical Campus Kaithal

[email protected] 2Assistant Professor, Department of Civil Engineering, GCET, Greater Noida

[email protected]

ABSTRACT

Clays are notoriously well known for giving rise to swelling problems and difficulties in

construction due to excessive settlement and limited strength. Hence, such types of soils need to

be stabilized before construction for improving their engineering properties. In soil stabilization,

cement is commonly used as a stabilizing agent, to simultaneously increase the strength and

stiffness of the originally weak, soft material. However cement is relatively expensive and

potentially harmful to the environment when admixed with soils. The need for alternative

stabilizing agents which could reduce the use of cement is therefore apparent. The objective of

the present study is to investigate shear strength characteristics as well as mechanical strength of

Kaolinite clay soil treated with 5, 10, 15, 20 and 25 % by weight of cement kiln dust. This has

been done to make the soil suitable to build pavements over it. Standard Proctor tests have been

conducted to determine optimum moisture content and maximum dry density of Kaolinite clay

and Kaolinite clay stabilized with 5, 10, 15, 20 and 25 % of CKD passing 425 micron IS sieve. It

has been observed that with increase in the percentage of cement kiln dust, OMC decreases and

MDD increases. The decrease in OMC with increase in cement kiln dust content may be

attributed to the addition of material which is classified as silty sand to the parent material. The

presence of cement kiln dust having higher specific gravity may be the cause for increase in

density. A series of unconfined compressive strength tests have been conducted to determine the

strength characteristics of Kaolinite clay treated with various percentages of cement kiln dust. It

has been observed that up to 20 % mixing of admixture, unconfined compressive strength (qu)

and undrained shear strength (cu) increase significantly then decrease with further increase in

percentage of stabilizer. It may be attributed to the addition of non-plastic silty material having

free lime content. However, when the same samples were tested for mechanical strength by

performing CBR tests, it has been observed that the CBR values increases with increase in

percentage of CKD. It may also be attributed to the addition of non-plastic silty material having

free lime content. Overall, it has been observed that the cement kiln dust effectively increases

strength and hence make clays suitable for building pavements over it.

INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND

TECHNOLOGY (IJCIET)

ISSN 0976 – 6308 (Print)

ISSN 0976 – 6316(Online)

Volume 4, Issue 1, January- February (2013), pp. 26-37

© IAEME: www.iaeme.com/ijciet.asp

Journal Impact Factor (2012): 3.1861 (Calculated by GISI)

www.jifactor.com

IJCIET

© IAEME



27

Keywords: Stabilization, Cement kiln dust (CKD), Maximum dry density (MDD), Optimum

moisture content (OMC), Stabilization, Unconfined compressive strength (qu) and Undrained

shear strength (Cu).

1. INTRODUCTION

Weak foundation soil conditions can result in inadequate support and reduce structural

life. Soil properties can be improved through the addition of chemical or cementatious additives

i.e stabilization [1]. Soil stabilization refers to the procedure in which a soil, a cementing

material, or other chemical material is added to a parent soil to improve one or more of its

properties. One may achieve stabilization by mechanically mixing the natural soil and stabilizing

material together so as to achieve a homogenous mixture or by adding stabilizing material to an

undisturbed soil deposit and obtaining interaction by letting it permeate through soil voids. These

chemical additives range from waste products to manufactured material which includes Portland

cement, Fly ash, chemical stabilizers and cement kiln dust. These additives can be used with

variety of soils to improve their native engineering properties. The effectiveness of these

additives depends on the soil treated and the amount of additive used. The high strength obtained

from cement and lime may not always be required, however, and there is justification for seeking

cheaper additives which may be used to alter soil properties.

Invariably, any one of two methods is used to accomplish soil stabilization – mechanical and

additive. The effectiveness of a stabilization process can be gauged by the uniformity in blending

the many materials. Usually, the preferred way of mixing is in a stationary or traveling plant.

However other methods like scarifies, plows, disks, graders, and rotary mixers, are also largely

practiced. The method of soil stabilization is decided by the amount of stabilization required and

the prevailing conditions. Care must be taken to ensure that an accurate soil description and

classification is procured in order to select the correct materials and procedures. Mechanical

Stabilization is done by mixing soils of two or more gradations to result in a material of the

required specifics. This mixing of the soil can take place at the construction site, at a central

plant, or at a borrow area. The blended material is then spread and compacted to required

densities. In additive method, an additive is any manufactured or commercial product that can be

used to improve the quality of the soil, when added in accurate quantities. Portland cement, lime,

lime-cement-fly ash and bitumen, alone or in combination, are commonly used additives to

stabilize soils. The selection and quantity of additive used depends entirely on the type of soil and

the degree of improvement required.

In this study, cement kiln dust (CKD) was used as an additive to improve the texture, compaction

properties and strength of kaolinite clay. Current study is based on the fact that when the

additives containing free calcium hydroxide are mixed with the soil, the calcium causes the clay

particles to flocculate into a more sand like structure reducing the plasticity of soil. Soil

stabilization includes the effects of modification with a significant additional strength gain. Since

the soil stabilization mechanism of fine grained soil requires calcium (in the form of lime) as the

major stabilizing agent, hence we can use CKD which contains high free lime for stabilization of

clay soil.

2. NEED FOR PRESENT STUDY

The shear strength is, without doubt, the most important engineering property of soil.

Also bearing capacity criteria or shear strength failure criteria must be satisfied for satisfactory

performance of foundations. Hence the most important design input parameter needed for

geotechnical design is soil’s shear strength [6].



28

There are three different type of failure mechanism, based on the pattern of shearing zones, have

been identified as general shear failure, local shear failure and punching shear failure. In clays,

punching shear failure is of great importance. It occurs in soils possessing the stress-strain

characteristics of a very plastic soil.

Typical features of this mode are:

a) Poorly defined shear planes

b) Soil zones beyond the loaded area being little affected.

c) Significant penetration of a wedge shaped soil zone beneath the foundation, accompanied

by vertical shear beneath the edges of the foundation.

d) Ultimate load cannot be clearly recognized.

Hence proper investigations regarding strength of soil must be done to ensure long serviceability

of pavements. The present work aims to understand the strength characteristics of kaolinite

treated with cement kiln dust. The globally growing demand of cement results in towering

collection of CKD from cement plants. The disposal of this fine dust is very difficult and poses a

serious environmental threat [7]. Our study also focuses on the reduction of the huge stock piles

of this material. A better understanding of these properties will enhance the usage of this material

in geotechnical engineering and highway engineering works.

3. MATERIALS USED

3.1 Kaolinite clay Clay mineral used in the experiments was collected from Starke & Co. Pvt. Ltd., 17

Najafgarh Road, Near Zakhira Chowk, New Delhi-110015. It was classified as CI (clay of

intermediate compressibility) as per specifications of IS: 1498 (1970) [2]. The chemical and

physical properties are reported in Table 1 and Table 2 respectively.

Table 1. Chemical properties of kaolinite clay

3.2 Cement kiln dust It was collected from Jaypee cement plant, Solan, Himachal Pradesh. It was classified as

SM as per specifications of IS: 1498 (1970) [2]. The physical properties are reported in Table 1.

Constituents Percentage By Weight

(%)

Al2O3 30.3

Fe2O3 1.5

TiO2 1.0

SiO2 56.2

CaO 0.56

MgO 0.90

Na2O + K2O 1.0

LOI 8.5



29

Table 2. Physical properties of materials

4. SAMPLE PREPARATION

The whole process of sample preparation is divided into three parts, 1)

Composition of samples, 2) Mechanical Mixing and 3) Static compaction.

4.1 Composition of specimens Specimens of Kaolinite clay and Kaolinite clay treated with 5, 10, 15, 20 and

25 % of cement kiln dust passing 425 micron IS sieve were prepared at maximum dry

density and optimum moisture content as per specifications of IS: 2720 (Part 7) (1974)

[3].

4.2 Mechanical mixing Oven dry soil was dry mixed with various percentages of oven dried cement

kiln dust (CKD). Sufficient quantity of water was then added to bring the moisture

content to the desired level. The mixture was then manually mixed thoroughly with a

spatula.

4.3 Static compaction Cylindrical specimens were compacted by static compaction in 3.9 cm

diameter split mould to the required height of 8.5 cm. The inner surface of the split

mould was smeared with oil to reduce friction during the extraction of sample. The

wet homogenous mixture was placed inside the split mould using spoon with

continuous tapping with spatula and leveled. The whole assembly was statically

compacted in loading frame to the desired density.

The sample was kept under static load for not less than 20 minutes in order to account

for any subsequent increase in height of sample due to swelling. All the specimens

were kept in polythene bags for maturing for three days.

Index Properties Materials

Kaolinite Clay Cement Kiln Dust

IS Classification CI SM

Specific Gravity 2.36 2.52

Liquid Limit 45

N P Plastic Limit 22

Plasticity Index 23

OMC 18% -

MDD 1.69 g/cc -

CBR (Unsoaked) 5.88 -

CBR (Soaked) 2.36 -



30

Fig. 1 Samples kept for maturing

5. ANALYSIS OF TEST RESULTS & DISCUSSION

The objective of the present study is to investigate strength characteristics of

Kaolinite clay soil treated with 5, 10, 15, 20 and 25 % by weight of cement kiln dust.

This has been done to make the soil suitable to build pavements over it. In order to

assess improvement in strength, unconfined compressive strength (qu), failure load

and undrained shear strength (cu) have been evaluated [8]. The results of these tests

have been analyzed under the following headings:

5.1 Moisture-density relationship Standard Proctor tests have been conducted to determine optimum moisture

content (OMC) and maximum dry density (MDD) of Kaolinite clay stabilized with

various percentages of cement kiln dust as per specifications of IS: 2720 (Part 7)

(1974) [3] and the results are tabulated in Table 3. For Kaolinite clay OMC and MDD

have been observed as 18 % and 1.69 g/cc respectively. For Kaolinite clay stabilized

with Cement kiln dust OMC varies from 19 to 16.5 % and MDD varies from 1.682 to

1.736 g/cc. It has been observed that with increase in the percentage of cement kiln

dust OMC decrease and MDD increases upto 20 % CKD content as an additive. But

beyond that, the value of MDD decreases and value of OMC increases. The decrease

in OMC with increase in cement kiln dust content upto 20 % may be attributed to the

addition of material which is classified as silty sand to the parent material. The

presence of cement kiln dust having higher specific gravity may be the cause for

increase in density.



31

Table3. Compaction characteristics of Kaolinite clay treated with various percentages of

cement kiln dust

Description Of Sample MDD

(g/cc)

OMC

(%)

Kaolinite + 5% CKD 1.682 19

Kaolinite + 10% CKD 1.692 18.7


Kaolinite + 20% CKD 1.768 15


Fig 2 to Fig 7 shows comparison of MDD and OMC for clay stabilized with various

percentages of cement kiln dust.

Fig 2. Moisture content vs Dry densitycurve for Kaolinite clay

Fig 3. Moisture content vs Dry density curve for Kaolinite clay + 5% CKD

1.5

1.55

1.6

1.65

1.7

0 10 20 30

Dry

Den

sity

in

g/c

c

Moisture Content (%)

1.5

1.55

1.6

1.65

1.7

0 10 20 30Dry

Den

sity

in g

/cc




32



Fig 6. Moisture content vs Dry density curve for Kaolinite clay +20 % CKD

Fig 7. Moisture content vs Dry density curve for Kaolinite clay +25 % CKD

1.55

1.6

1.65

1.7

1.75

0 10 20 30Dry

Den

sity

in

g/c

c


1.4

1.5

1.6

1.7

1.8

0 20 40

Dry

Den

sity

in

g/c

c


1.55

1.6

1.65

1.7

1.75

1.8

0 10 20 30

Dry

Den

sity

in

g/c

c


1.55

1.6

1.65

1.7

1.75

0 10 20 30Dry

Den

sity

in g

/cc




33

5.2 California bearing ratio

California bearing ratio (CBR) tests were conducted to determine mechanical

strength of kaolinite clay treated with cement kiln dust in soaked as well as unsoaked

condition as per specifications of IS: 2720 (Part 16) (1987)[5]. It has been observed that

value of CBR in both conditions increases with increase in CKD content as additive. In

unsoaked condition CBR varies from 6.78 to 9.21 and in soaked condition it varies from

2.84 to 3.147. CKD Values for all samples are reported in Table 4 and represented in

Figure 8.

Table 4. CBR values of kaolinite samples stabilized with CKD

Description Of Sample CBR

(Unsoaked)

CBR

(Soaked)






Fig. 8 Variation of CBR values with percentage of CKD content

0123456789

10

0 10 20 30

CB

R v

alues

Percentage of CKD content (%)

CBR

(Unsoaked)

CBR

(Soaked)



34

5.3 Strength Characteristics

A series of unconfined compressive strength tests were conducted to determine the

strength characteristics of Kaolinite clay treated with various percentages of cement kiln

dust as per specifications of IS: 2720 (Part 10) (1973) [4] and the results are tabulated in

Table 5. It has been observed that unconfined compressive strength (qu) and undrained

shear strength (cu) increase with increase in percentage of CKD upto 20 %. Further

increase in percentage of CKD as stabilizer leads to decreased values of qu and cu. This

can be attributed to the addition of non-plastic silty material having free lime content.

Fig.9 shows comparison of cu for Kaolinite clay stabilized with various percentages of

cement kiln dust.

Table 5. Strength characteristics of Kaolinite clay treated with various percentages of

cement kiln dust

Fig. 9 Undrained shear strength Vs. Percentage of CKD as stabilizer

0

0.5

1

1.5

2

2.5

3

3.5

Undra

ined

shea

r st

regnth

Percentage of CKD asstabilizer (%)

Description Of Sample Failure Load

(kg)

UCS

qu

(kg/cm2)

Undrained Shear

Strength Cu

(kg/cm2)

Kaolinite 23.85 1.691 0.845

Kaolinite + 5% CKD 74.1 5.254 2.627

Kaolinite + 10% CKD 74.7 5.517 2.758

Kaolinite + 15% CKD 75.3 5.636 2.818

Kaolinite + 20% CKD 77.26 5.782 2.891

Kaolinite + 25% CKD 78 5.684 2.842



35

The failure patterns of kaolinite clay samples treated with various percentage of CKD

content are shown in Fig. 10 to 15.

Fig. 10 Failure pattern of axially loaded sample of Kaolinite

Fig. 11 Failure pattern of axially loaded sample of Kaolinite + 5% CKD





36

Fig. 13 Failure pattern of axially loaded sample of Kaolinite +20 % CKD


6. CONCLUSIONS

The study demonstrates the influence of cement kiln dust on the strength

characteristics of Kaolinite clay. The following conclusions have been drawn based on the

laboratory investigations carried out in this study:

1. It has been observed that with increase in the percentage of cement kiln dust OMC

decrease and MDD increases. The decrease in OMC with increase in cement kiln dust

content may be attributed to the addition of material which is classified as silty sand

to the parent material. The presence of cement kiln dust having higher specific gravity

may be the cause for increase in density.

2. Strength analysis of the kaolinite clay and Kaolinite clay stabilized with various

percentages of cement kiln dust indicates that up to 20 % mixing of admixture qu and

cu increases then decreases. It can be attributed to the addition of non-plastic silty

material having free lime content. However, it has been observed that mechanical

strength evaluated from CBR test increases with increase in CKD content.

The study shows that treatment of soil with cement kiln dust is an effective method of

stabilization of problematic soils.

To summarize, use of this industrial wastes is a beneficial proposition which is economical

and environment friendly as well. Results of this study can be used in construction of

pavements over CKD stabilized clay beds.



37

REFERENCES

[1] Ho Meei-Hoan, Tarmizi Ahmad, Chan Chee-Ming and Bakar Ismail (2011),

“Leachability and Strength of kaolin Stabilized With Cement and Rubber”,

International Journal of Sustainable Construction Engineering & Technology, Vol.2,

Issue1.

[2] IS: 1498 (1970),”Indian Standard Methods of Test for Soils: Classification and

Identification of Soil for General Engineering Purposes”, Bureau of Indian Standards.

[3] IS: 2720 (Part 7) (1974), “Indian Standard Methods of Test for Soils: Determination

of Moisture Content-Dry Density Relation using Light Compaction”, Bureau of

Indian Standards.

[4] IS: 2720 (Part 10) (1973), “Determination of Unconfined Compressive Strength”,

Bureau of Indian Standards.

[5] IS: 2720 (Part 16) (1987), “Indian Standard Methods of Test for Soils: Laboratory

determination of CBR”, Bureau of Indian Standards.

[6] Ranjan, Gopal and Rao, A.S.R. (2000), “Basic and Applied Soil Mechanics”, New

Age International (P) Ltd., New Delhi.

[7] Robert L. Parsons, Elizabeth Knee Bone, Justin P. Milburn (2004), “Use o Cement

Kiln Dust For Sub-Grade Stabilization”.

[8] Singh, Alam and Chowdhary, G.R. (1994), “Soil Engineering in Theory and

Practice”, Geotechnical Testing and Instrumentation, Vol. 2, CBS Publishers and

Distributors, Delhi.

Documents

Stabilization of weak pavement subgrades using cement kiln dust 2