CHEMICAL ENGINEERINGTRANSACTIONS 
 

VOL. 51, 2016 

A publication of 

 
The Italian Association 

of Chemical Engineering 
Online at www.aidic.it/cet 

Guest Editors:Tichun Wang, Hongyang Zhang, Lei Tian 
Copyright © 2016, AIDIC Servizi S.r.l., 

ISBN978-88-95608-43-3; ISSN 2283-9216 

Experimental Study On Chemical Consolidation Of Expansive 
Soil Subgrade 

Xinzheng Wang*a, Jian Zhanga, Ping Heb 
aAcadedemy of Civil Engineering and Architechure, Nanyang Normal University, Nanyang 473061,China 
bAcadedemy of Art and Design, Nanyang Normal University, Nanyang 473061,China 
wxz791023@126.com 

Much attention on the use of expansive soils has been paid because of the special engineering characteristics 
and morphology and the damage effects as well. Many methods have been used to reduce the damage 
effects caused in the application of expansive soils during recent years. One of the effective methods is the 
chemical consolidation due to high cost-performance ratio. Testing specimens are subjected to physical 
properties, compaction, free swell index and swell potential, swelling pressure, and unconfined compressive 
strength tests in laboratory. The paper contrasts and analyses the relationship between the optimum water 
content, the maximum dry unit weight, the unconfined compressive strength and CBR with different ratio of 
added lime after expansive soils have been improved. The experiment confirms the optimal ratio of added lime 
and the result of the experiment is significant to similar projects. 

1. Introduction 

Expansive soil is composed of a great deal of strong hydrophilic clay minerals, such as montmorillonite and 
illite, it has much character, such as expansive construction, many cracks, strong expansive and contraction, 
intensity decadence(Liao,1984). Engineering damages happen frequently for highway construction in 
expansive soil areas, such as pavement crack, subsidence, bump, side slope collapse, and embankment 
instability. According to regulations on subgrade filler in expansive soil areas in the Specifications for Design 
of Highway Subgrade, expansive soils are forbidden to be used as subgrade filler in principle, especially for 
high-strength expansive soils. If medium-strength expansive soils or weak expansive soils have to be used 
because of limited conditions, it is necessary to test the used soil to find corresponding treatment measures in 
case those bad consequences emerge after construction(Kong, 2004; Hui, 2005; Yang, 2011). 
The common improvement method for expansive soils is chemical modification. Some materials, such as lime, 
cement, fly ash, chloride, asphalt, synthetic of curing agent and synthetic resin etc are blended with expansive 
soils for a series of physicochemical reaction, aiming to reduce swelling potential of expansive soils, enhance 
soil strength and water stability, and improve the mechanical properties as well. Considering the improvement 
effect and economic cost of the improved agent, lime-improved expansive soils are verified to be more 
economical and effective method to improve the treatment of expansive soil. The paper undertook 
experimental research on the subgrade filler of expansive soils in LuoYang-NanYang Highway construction. 
The results will serve as reference and guidance for future highway engineering and other construction work in 
expansive soil areas(Yang, 2007; Bian, 2016; Wang, 2014; Lu, 2009).  

2. Improvement mechanism of lime improved expansive soil 

As an inorganic cementing material, lime can harden in either air or water. The property of lime is determined 
by the contents of CaO and MgO. The higher the contents, the greater the activity, and the stronger the 
cementing capacity is as well. Both the physical reaction and the chemical reaction were happened during the 
process of lime treatment, the two kinds of reactions makes the soil properties change radically(Li,1992; 
Huang, 2009; Li, 2005; Lian, 2011). 
(1)Lime nitration. Quick lime is decomposed and transformed into Ca(OH)2 and heat is released at the same 
time. The reaction results are: one is Cao nitrification process reduces the expansive soil moisture content; 

                               
 
 

 

 
   

                                                  
DOI: 10.3303/CET1651027

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Please cite this article as: Wang X.Z., Zhang J., He P., 2016, Experimental study on chemical consolidation of expansive soil subgrade, 
Chemical Engineering Transactions, 51, 157-162  DOI:10.3303/CET1651027   

157



second is the formation of Ca(OH)2 volume increased nearly doubled. Both the results help agglomerate and 
strengthen expansive soils. The relative equation is: 

22
)(OHCaOHCaO                                                                                                                            (1) 

(2)Cation exchange. Under the influence of soil water, quick lime is decomposed rapidly and transformed into 
Ca(OH)2 and a little Mg(OH)2, following the further dissociation of Ca2+ and Mg2+. Ca2+ and Mg2+are 
exchanged with Na+, K+ and H+ on the surface of soil particles, entailing thinned diffusion layer of the double-
layer soil colloid. Also, the infiltrated swelling volume is lowered, the bonding force between soil particles is 
enhanced, and the soil mass strength is improved as well. Therefore, the subsequent fast agglomerations of 
soil particles help improve preliminary soil mass strength. This reaction can be expressed in the following 
formula: 

      NaOnHOHSiAlCaCaOnHOHSiAlNa
221042

22

221042
)(0)(0              (2) 

(3)Carbonation. The generated Ca(OH)2 and Mg(OH)2 in the soil can further react to CO2 to form rough solid 
CaCO3 and MgCO3 solid particles, with high strength and water stability. Soil cementation by CaCO3 
reinforces the soil mass to form lime-stabilized soil; the strength of the lime soil is gradually strengthened. 
Relative reaction can be expressed as: 

OHCaCOCOOHCa
2322

)( 
                                                                  (3) 

(4)Gelling reaction. After the cation exchange, lime reacts to SiO2 and Al2O3 in the soil mass to form 
complicated composite including calcium metasilicate and calcium aluminate. In this process, strong 
cementation happens. The content of clayey minerals with water-swelling property is reduced, resulting in an 
appreciable improvement of post-stage strength and durability of the limestone soil(Wang, 2009; Wang, 2014). 

3. Test materials and methods 

3.1 Test materials 
The expansive soil for test use was extracted from a worksite in LuoYang-NanYang Highway. The 
middle expansive soil presented the colour of mostly brown-yellow and slight brown-red, grey-green and grey-
white. The smooth and hard fracture surface with dense structure was formed due to lack of water, and 
underwent tests for its mineral components as follows: montmorillonite19.3%, illite 38.5%, chlorite7.7%, 
quartz12 %, kaolin 6.2%, hydromica5.5 %, feldspar5.8 %, and calcite 5 %. The quick lime for the test was 
extracted from NanYang city (the content of CaO and MgO in the lime is higher than 70%). 

3.2 Test methods 
Chapter 2 The laboratory test was undertaken according to the Test Methods of Soils for Highway Engineering 
(JTJ051—2004). The lime-doped rate, namely the ratio between the quality of quick lime and that of the dry 
soil, is an important factor that influences the improvement effect. During the laboratory test, certain quality of 
quick lime was weighed pro rata for decomposition and subsequent blending with dry soil. An analytical test 
was undertaken for the mixture’s physical property, including mineral component, liquid limit, plastic limit, and 
particle size. There were also respective tests for the samples without lime and for the lime-compaction 
samples on the shrink–swell capacity in different ages and the mechanical properties, such as swelling force, 
free swelling ratio and loaded swelling ratio, compaction test, shrinkage test, CBR test, and unconfined 
compressive strength test. Five lime-doped rates were adopted in the test, namely 2%, 4%, 6%, 8% and 10%. 
Through the above tests, various indices were obtained before and after the expansive soil are improved at 
different lime-doped rates. Corresponding test data was analyzed, aiming at the optimum improvement effect. 

Table 1: Comparison results of particle size before and after improving expansive soils 

particle size 
/mm 

lime ratio /% 
0 2 4 6 8 10 

＞0.25 0 6.3 11.2 17.4 17.2 18.7 
0.25~0.075 2.1 12.3 15.7 18.3 18.9 18.2 

0.075~0.005 35.5 65.2 61.9 56.5 56.6 45.6 
＜0.005 62.4 16.2 11.2 7.8 7.3 10.7 

 

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4. Test results and analysis 

4.1 Particle grading 
Table 1 shows the comparison results of particle size before and after improving expansive soils, and the 
change degree of particle grading of the improved expansive soils can be seen from the table. The 
improvement changes particle grading greatly, and the overall trend is: the fine particle content (especially the 
content of clay particle) drops significantly from 62.4% to 7.3%～16.2%; the fly ash particle content increases 
from 35.5％ to 45.6％～65.2％; the coarsening sand particle gains its content prominently. The more the lime is 
incorporated, the higher the coarsening degree. 

4.2 Compaction characteristics 
In order to control the quality of subgrade filler, we must master the compaction characteristics of the filler. 
The necessary and sufficient condition for control on the quality of subgrade filler is to obtain the maximum dry 
density and optimal water content of the filler in advance through compaction tests. Figure 1 shows the 
relationship curves of the compaction characteristics and the ratio of added lime. As can be seen, after the 
lime is incorporated, with the increase of the lime rate, the optimal water rate increases from 17.5% to 19.2%, 
while the maximum dry density decreases from 1.78g.cm-3 to 1.656 g.cm-3.  
 

17

17.2

17.4

17.6

17.8

18

18.2

18.4

18.6

18.8

19

19.2

19.4

-2 0 2 4 6 8 10 12

lime rate/%

o
p
t
i
m
u
m
 
w
a
t
e
r
 
r
a
t
e
/
%

1.6

1.62

1.64

1.66

1.68

1.7

1.72

1.74

1.76

1.78

1.8

m
a
x
i
m
u
m
 
d
r
y
 
d
e
n
s
i
t
y
/
g
.
c
m
-
3

optimum water rate/%

maximum dry density/g.cm-3

 

Figure 1: The relationship curves of the 

compaction characteristics and the ratio of added 

lime  

 

5
10
15
20
25
30
35
40
45
50
55
60

-2 0 2 4 6 8 10 12

lime rate/%

l
i
q
u
i
d
/
p
l
a
s
t
i
c
 
l
i
m
i
t
/
%

5

10

15

20

25

30

p
l
a
s
t
i
c
i
t
y
 
i
n
d
e
x

liquid limit/%

plastic limit/%

plasticity index

 
 

Figure 2: The relationship curves for the liquid limit 

test and the plastic limit test 

4.3 Change of liquid limit and plastic limit 
Figure 2 shows the relationship curves for the liquid limit test and the plastic limit test. As can be seen, the 
plasticity index of the lime soil decreases from 28.8 to 8.2 as the ratio of added lime increases. The reason is 
that the plastic limit increases as the ratio of added lime increases. The shrink–swell capacity for the lime-
doped expansive soils is realized primarily by reducing soil plasticity. When a certain amount of lime is added 
to the expansive soils, the plasticity index drops significantly, the hydrophilic weakens significantly, and the 
soil structure changes as well. Thus, the shrink–swell capacity weakens. 

Table 2: The results for expansion and shrinkage test 

lime 
ratio /% 

instar/d 

expansion test shrinkage test 
non-pressure 

expansive rate 
/% 

50KPa expansive 
rate /% 

expansive 
force /Kpa 

shrinking 
limit /% 

shrinking ratio 
/% 

0  36 9.3 284 16.2 3.1 
6 
6 

7 0.5 0 9.6 5.2 1.9 
28 0.2 0 0.7 4.3 1.07 

 

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4.4 Change of swelling shrinkage of expansive soil after added lime 
In order to research on the influence of lime mixture on the shrink–swell capacity, the paper undertook 
expansion test and shrinkage test for the expansive soil with no lime and with 6% lime, respectively. The 
results are shown in Table 2. As can be seen, when there is no lime added, the non-pressure expansive rate 
is 36%, the expansive rate under 50kPa is 9.3%, the expansive force is 284kPa, and the shrinkage ratio is 
3.1%. The above ratios all drop significantly after 6% lime is incorporated. Therefore, addition of lime to the 
expansive soil can significantly reduce its expansibility, and can effectively lower shrinking deformation after 
construction. 
Table 2 also shows that all the tested indices for the soil with 6% lime after 28 days conservation are smaller 
than that after 7 days conservation. This means that with the conservation instar increases, the effect for lime 
in reducing expansibility and lowering shrinking deformation increases. Thus, attention should be paid to instar 
conservation during construction so as to reach optimal construction effects. 

4.5 The CBR test before and after lime is incorporated 
Figure 3 shows the relationship curve between the CBR value of the improvement soil and different ratio of 
added lime. As can be seen, the CBR value is low when there is no lime; as the ratio of added lime increases, 
the CBR value increases prominently until to the peak where the lime rate is 8% and begins to drop again. 
 

0

20

40

60

80

100

120

0 2 4 6 8 10 12

lime rate/%

C
B
R

 

Figure 3: The relationship curve between the CBR value of the improvement soil and different ratio of added 

lime  

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 2 4 6 8 10 12

lime rate/%

u
n
c
o
n
f
i
n
e
d
 
c
o
m
p
r
e
s
s
i
v
e
 
s
t
r
e
n
g
t
h

/
M
p
a

7d

28d

 

Figure 4: The relationship curves between unconfined compressive strength and different ratio of added lime 

at the instar of 7d and 28d 

4.6 Unconfined compressive strength test 

It is simple, feasible and easy to operate to determine the optimal ratio of added lime by the unconfined 
compressive strength test. Figure 4 shows the relationship curves between unconfined compressive strength 
and different ratio of added lime at the instar of 7d and 28d. The optimal lime-doped rates at 7d and 28d are 
found to be the lime-doped rates at curve peaks. 
As can be seen, when the ratio of added lime increases, the unconfined compressive strength for the lime-
doped saturated soil first increases and then decreases. This is because Ca2+in the lime replaces lower-
valence cation in the expansive soil (Na+ in the surface of clay particles, for example). The remaining Ca2+may 

160



be absorbed, which causes the total quality of ion to increase. When lime is incorporated into the soil, soil 
structure changes due to flocculation of clay particles. Therefore, as clay content is decreased due to the 
increase of lime rate, the shrink–swell degree drops correspondingly and the lime soil strength is increased. 
However, the excessive lime that is left after the compaction process blocks combination of soil particles, thus 
leading to the decrease of lime soil strength. 

5. Conclusion 

To add lime to expansive soils is to lower soil expansibility and to improve soil strength. As ratio of added lime 
increases, various indices decreases in varying degrees, including clay particle content, maximum dry density, 
plasticity index, swelling rate. This proves the feasibility of the method of lime-improved expansive soils. 
However, the improvement effect of expansive soils may decrease in turn when lime rate increases too much. 
For example, in the CBR test and the unconfined compressive strength test, with the increase of lime rate, 
both the CBR value and the unconfined compressive strength first increases and then decreases. So, there is 
optimal ratio of added lime in the improvement of expansive soils (Wang, 2005).. 
The improvement of expansive soils can result in reduction of large amount of disused soil in construction 
areas, of occupied area of land, and of the increasing engineering cost due to borrow fill. In areas with large 
distribution of expansive soils, local materials can be used for laboratory fitting test according to the free 
swelling rate and the swelling potential. After the improvement effect of mechanical properties is determined 
for different fitting rates, the optimal fitting rate will be chosen to meet the engineering demand. On the 
premise that strength and other design requirements are guaranteed, the lime amount should be reduced 
properly, aiming at shortening construction periods, lowering construction cost, and reducing engineering 
damages as well(Zhou,2012).. 

Acknowledgments  

The authors are grateful to the anonymous referees for their valuable remarks and helpful suggestions, which 
have significantly improved the paper. This research is supported by the national natural 
science foundation of China (Grant No: 41402267); Natural Science Basic Research projects of the Education 
Department of Henan Province (Grant No: 15B560008).the Youth Projects of NanYang Normal University 
(Grant No: QN2010008, QN2014018) 

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