Stabilization of weak pavement subgrades using cement kiln dust 2

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND
ISSN 0976 – 6316(Online) Volume 4, Issue 1, January- February (2013), © IAEME
TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 4, Issue 1, January- February (2013), pp. 26-37
IJCIET
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STABILIZATION OF WEAK PAVEMENT SUBGRADES USING
CEMENT KILN DUST

Brijesh Kumar1, Nitish Puri2
1
Assistant Professor, Department of Civil Engineering, HCTM Technical Campus Kaithal
brijesh.k.thakur@gmail.com
2
Assistant Professor, Department of Civil Engineering, GCET, Greater Noida
nitishpuri.ce.89@gmail.com

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.

26


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].

27


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
Percentage By Weight
Constituents
(%)
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

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.

28


Table 2. Physical properties of materials

Materials
Index Properties
Kaolinite Clay Cement Kiln Dust
IS Classification CI SM
Specific Gravity 2.36 2.52
Liquid Limit 45
Plastic Limit 22 NP
Plasticity Index 23
OMC 18% -
MDD 1.69 g/cc -
CBR (Unsoaked) 5.88 -
CBR (Soaked) 2.36 -

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.

29


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.

30


Table3. Compaction characteristics of Kaolinite clay treated with various percentages of
cement kiln dust

MDD OMC
Description Of Sample
(g/cc) (%)

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.

1.7
Dry Density in g/cc

1.65
1.6
1.55
1.5
0 10 20 30
Moisture Content (%)

Fig 2. Moisture content vs Dry densitycurve for Kaolinite clay

1.7
Dry Density in g/cc

1.65
1.6
1.55
1.5
0 10 20 30

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

31


1.75

Dry Density in g/cc
1.7
1.65
1.6
1.55
0 10 20 30
1.8
Dry Density in

1.7
1.6
g/cc

1.5
1.4
0 20 40

1.8
Dry Density in g/cc

1.75
1.7
1.65
1.6
1.55
0 10 20 30

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

1.75
Dry Density in g/cc

1.7
1.65
1.6
1.55
0 10 20 30

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

32


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

CBR CBR
Description Of Sample
(Unsoaked) (Soaked)






10
9
8 CBR
7 (Unsoaked)
CBR values

6
5
4
3 CBR
2 (Soaked)
1
0
0 10 20 30
Percentage of CKD content (%)

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

33


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

UCS Undrained Shear
Failure Load
Description Of Sample qu Strength Cu
(kg)
(kg/cm2) (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

3.5

3
Undrained shear stregnth

2.5

2

1.5

1

0.5

0
Percentage of CKD asstabilizer (%)

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

34


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



35


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.

36


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.

37

Stabilization of weak pavement subgrades using cement kiln dust 2

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