laboratory studies on exapnsive lime

Laboratory Studies on Stabilization of an ExpansiveSoil by Lime Precipitation TechniqueT. Thyagaraj1; Sudhakar M. Rao2; P. Sai Suresh3; and U. Salini4

Abstract: Lime stabilization prevails to be the most widely adopted in situ stabilization method for controlling the swell-shrink potentialsof expansive soils despite construction difficulties and its ineffectiveness in certain conditions. In addition to the in situ stabilizationmethods presently practiced, it is theoretically possible to facilitate in situ precipitation of lime in soil by successive permeation of calciumchloride (CaCl2) and sodium hydroxide (NaOH) solutions into the expansive soil. In this laboratory investigation, an attempt is made to studythe precipitation of lime in soil by successive mixing of CaCl2 and NaOH solutions with the expansive soil in two different sequences.Experimental results indicated that in situ precipitation of lime in soil by sequential mixing of CaCl2 and NaOH solutions with expansivesoil developed strong lime-modification and soil-lime pozzolanic reactions. The lime-modification reactions together with the poorly de-veloped cementation products controlled the swelling potential, reduced the plasticity index, and increased the unconfined compressivestrength of the expansive clay cured for 24 h. Comparatively, both lime-modification reactions and well-developed crystalline cementationproducts (formed by lime-soil pozzolanic reactions) contributed to the marked increase in the unconfined compressive strength of the ex-pansive soil that was cured for 7–21 days. Results also show that the sequential mixing of expansive soil with CaCl2 solution followed byNaOH solution is more effective than mixing expansive soil with NaOH solution followed by CaCl2 solution. DOI: 10.1061/(ASCE)MT.1943-5533.0000483. © 2012 American Society of Civil Engineers.

CE Database subject headings: Expansive soils; Soil stabilization; Compressive strength; Swelling (material); Shrinkage; Lime;Laboratory tests.

Author keywords: Expansive soils; Soil stabilization; Compressive strength; Swelling; Shrinkage; Lime.

Introduction

Expansive soils occur in arid and semiarid regions of the world.The high swelling and shrinkage potentials of these soils cause se-vere damages to pavements, runways, and building foundations,which are founded on these soils (Chen 1988; Nelson and Miller1992). Chemical stabilization is one of the alternative solutions toovercome the undesirable swell-shrink potentials of the expansivesoils. Among the chemical stabilization methods for expansivesoils, lime stabilization is most widely adopted method for control-ling the swell-shrink potentials by chemically modifying the soilcharacteristics.

Lime stabilization of expansive soils in the field is achievedby shallow mixing of lime or by in situ deep stabilization methodsusing lime columns, lime piles, and lime slurry injection methods(Bell 1988b; Rao and Thyagaraj 2003). Physical mixing of lime

and soil is the most efficient and cost-effective method of stabiliz-ing expansive soils to shallow depths (Rao and Thyagaraj 2003).In situ stabilization methods using lime have been pioneered inSweden, Japan, and the United States, and these methods aremostly restricted to improve the engineering properties of soft clays(Tsytovich et al. 1971; Broms and Boman 1975; Holm et al. 1981;Bell 1988b; Wang 1989; Chew et al. 1993; Porbaha 1998; Rogerset al. 2000).

In situ stabilization methods using lime can be divided into threeprimary groups: lime columns, lime piles, and lime slurry injection(Glendinning and Rogers 1996). Lime columns refer to deep ver-tical columns of lime-stabilized material formed by in situ mixingof lime and soft clays. Lime column stabilization is mostly re-stricted to soft clays, because the construction of lime columnsin expansive soil deposits by in situ mixing of lime and expansivesoils is very difficult owing to the very stiff nature of these soils.Lime piles refer to holes in the ground filled with lime. Recently,Rao and Venkataswamy (2002) found that lime pile treatment ofexpansive soils could not promote soil-lime pozzolanic reactions;it only facilitated short-term lime-modification reactions. Lime piletreatment of expansive soil could not raise the soil pH levels to ≥ 12owing to the low solubility of lime and the impervious nature ofexpansive soil, which inhibited the migration of lime.

Long-term soil-lime pozzolanic reactions occur at pH values> 12 from the increase in the solubility of siliceous and aluminouscompounds in the clay minerals. These compounds react with cal-cium to form calcium silicate hydrate (CSH) and calcium aluminatehydrate (CAH) gels, which coat the soil particles and subsequentlycrystallize to bond them (Eades and Grim 1960; Diamond et al.1963; Rogers et al. 1997). Because of the imperviousness and verystiff nature of the expansive soils, the lime column and lime pilestabilization methods are either difficult to construct or ineffective

1Assistant Professor, Dept. of Civil Engineering, Indian Institute ofTechnology Madras, Chennai 600 036, India (corresponding author).E-mail: [email protected]

2Professor, Dept. of Civil Engineering, and Chairman, Center forSustainable Technologies, Indian Institute of Science, Bangalore 560 012,India.

3Former Postgraduate Student, Dept. of Civil Engineering, NationalInstitute of Technology Warangal, Warangal 506 004, India.

4Research Student, Dept. of Civil Engineering, Indian Institute ofTechnology Madras, Chennai 600 036, India.

Note. This manuscript was submitted on February 16, 2011; approvedon January 23, 2012; published online on January 25, 2012. Discussionperiod open until January 1, 2013; separate discussions must be submittedfor individual papers. This paper is part of the Journal of Materials in CivilEngineering, Vol. 24, No. 8, August 1, 2012. ©ASCE, ISSN 0899-1561/2012/8-1067–1075/$25.00.

JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / AUGUST 2012 / 1067

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http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0000483




in stabilizing these soils. Hence, a need exists for new treatmentmethods and for improvement of stabilization methods, whichcan effectively stabilize expansive soils.

In addition to migration of lime into the expansive soil froma lime pile/column, it is theoretically possible to facilitate in situprecipitation of lime in the expansive soil by successive permeationof calcium chloride (CaCl2) and sodium hydroxide (NaOH) solu-tions into the expansive soil. Successive permeation of CaCl2 andNaOH solutions is expected to facilitate in situ precipitation of limeaccording to the reaction

CaCl2 þ 2NaOH ⇒ CaðOHÞ2 þ 2NaCl ð1ÞThe precipitated lime is expected to modify the properties ofexpansive soil by lime-modification and soil-lime pozzolanicreactions.

In this laboratory investigation, an attempt is made to under-stand and develop criteria for in situ stabilization of expansive soilby sequential mixing of CaCl2 and NaOH solutions with expansivesoil in two different sequences. The effect of consecutive mixingof CaCl2 solution and NaOH solution in two different sequenceson the physicochemical properties, index properties, swell poten-tial, and unconfined compressive strength (UCS) of compactedexpansive soil are evaluated.

Materials and Methods

Materials

Expansive soil from the National Institute of TechnologyWarangal,Andhra Pradesh, India, was used in this investigation. The soil wasair dried and pulverized to pass through a 2-mm sieve. The soil-passing 2-mm sieve was used for conducting standard Proctorcompaction, oedometer swell potential, and UCS tests. Index prop-erties were determined on the soil fraction passing through a425-μm sieve. Commercial-grade CaCl2 and NaOH were usedfor preparing CaCl2 and NaOH solutions in this investigation.

Properties of Representative Expansive Soil

The pH of the representative soil was obtained by standard method.Soil-water suspension with a solids-to-water ratio of 1∶2:5 was usedin the determinations. Initial consumption of lime (ICL) of theexpansive soil was determined according to BS 1924 (BritishStandards Institution 1990). The ICL value of expansive soil cor-responded to 2.5%. The specific gravity (Gs) of the expansive soilspecimen was determined according to IS 2720 (Part 3) (Bureau ofIndian Standards 1980a). The grain size distribution of the expan-sive soil specimen was determined according to IS 2720 (Part 4)(Bureau of Indian Standards 1985a). Atterberg limits of the expan-sive soil specimen was determined according to IS 2720 (Part 5;Bureau of Indian Standards 1985b) and IS 2720 (Part 6; Bureauof Indian Standards 1972). The standard Proctor compaction testwas performed according to IS 2720 (Part 7; Bureau of IndianStandards 1980b). The expansive clay has a maximum dry density(MDD) of 1:45 Mg∕m3 and optimum moisture content (OMC) of25%. Table 1 shows the physicochemical properties, index proper-ties, and engineering properties of the expansive soil used in thisinvestigation.

Procedure for Precipitation of Lime

As stated, it is theoretically possible to facilitate in situ precipitationof lime in the soil by sequential permeation/mixing of CaCl2 and

NaOH solutions into the expansive soil. According to the reactionin Eq. (1), 110 g of CaCl2 reacts with 80 g of NaOH to form 74 g ofcalcium hydroxide [CaðOHÞ2]. In Eq. (1), the weights of CaCl2 andNaOH combining to form CaðOHÞ2 are in the ratio of 1:375∶1(110∕80 ¼ 1:375). Maintaining the same ratio, 10% CaCl2 solu-tion and 7.3% NaOH solution were mixed sequentially with theexpansive soil to precipitate 2.5% lime in the soil. A 10% CaCl2solution was prepared by dissolving 10 g of CaCl2 in 100 mL ofdistilled water and 7.3% NaOH solution was prepared by dissolv-ing 7.3 g of NaOH in 100 mL of distilled water. To increase theamount of lime precipitation, the expansive soil was mixed withhigher concentrations of CaCl2 and NaOH solutions.

To bring out the significance of sequence of mixing CaCl2 andNaOH solutions on the expansive soil properties, the expansivesoil was mixed with CaCl2 and NaOH in two different sequences.In the first sequence, expansive soil was mixed with CaCl2 solutionbefore mixing with NaOH solution. This paper refers to experi-ments performed with this sequence of mixing CaCl2 and NaOHsolutions with expansive soil as Series 1 experiments. In the secondsequence, NaOH solution was mixed before CaCl2 solution. Thispaper refers to experiments performed with this sequence of mix-ing NaOH and CaCl2 solutions with expansive soil as Series 2experiments.

Index Properties

Because the liquid limit of untreated expansive soil was 75%, 120 gof air-dried expansive soil passing 425 μm was mixed with 45 mLof CaCl2 solution of desired concentration (10, 20, 35, 50 or 65%)and placed in an air tight polythene bag for moisture equilibrationfor 1 h. After this equilibration time, 45 mL of NaOH solution ofdesired concentration (7.3, 14.6, 25.5, 36.4 or 47.3%) was mixedwith expansive soil and placed in desiccators for moisture equili-bration for 24 h. Index properties were determined on the moisture-equilibrated specimens to find the effect of sequential mixing ofCaCl2 and NaOH solutions on expansive soil. Index properties per-formed with this sequence of mixing CaCl2 and NaOH solutionswith expansive soil are referred to as Series 1 experiments.

In Series 2 experiments, 45 mL of NaOH solution of desiredconcentration (7.3, 14.6, 25.5, 36.4 or 47.3%) was mixed with ex-pansive soil and placed in desiccators for moisture equilibration

Table 1. Properties of Expansive Soil

Property Value

pH 8.0

Specific gravity (GS) 2.70

Liquid limit (%) 75

Plastic limit (%) 25

Plasticity index (%) 50

Shrinkage limit (%) 13

Grain size distribution: (%)

Sand 16

Silt 28

Clay 56

Unified soil classification symbol CH

Compaction characteristics:

Maximum dry density (Mg∕m3) 1.45

Optimum moisture content (%) 25

Oedometer swell potential at 6.25 kPaa (%) 4.95

Unconfined compressive strengtha (kPa) 127aSpecimen compacted at optimum moisture content to maximum drydensity.

1068 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / AUGUST 2012

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for 1 h. After 1-h equilibration time, 45 mL of CaCl2 solution ofdesired concentration (10, 20, 35, 50 or 65%) was mixed with ex-pansive soil and placed in desiccators for moisture equilibrationfor 24 h. Index properties were determined on the moisture-equilibrated specimens for finding the effect of sequential mixingof NaOH and CaCl2 solutions on expansive soil. Table 2 showsdetails of the CaCl2 and NaOH solution concentrations used andthe sequence of mixing CaCl2 and NaOH solutions with the expan-sive soil.

Table 2 also shows the calculated amount of lime precipitationin the soil and the percentage of lime precipitation by dry weight ofsoil. The amount of lime precipitation in the soil is calculated onthe basis of Eq. (1). According to the Eq. (1), 110 g of CaCl2 reactswith 80 g of NaOH to form 74 g of CaðOHÞ2. When 45 mL of 10%CaCl2 solution and 45 mL of 7.3% NaOH solution are mixed se-quentially with the expansive soil, the amount of lime precipitationin the soil may be calculated as

74110

×10100

× 45 ¼ 3:03 g ð2Þ

By knowing the dry weight of the soil, the percentage of limeprecipitated in the soil can be calculated.

Oedometer Swell Potential Tests

All of the specimens for oedometer swell tests were compactedin oedometer rings of 60-mm diameter and 20-mm height, whichneeded 57.4 g of expansive soil by dry weight (dry density ¼1:45 Mg∕m3) for 14-mm thick specimens. A total of 57.4 g of ex-pansive soil passing 2 mmwas thoroughly hand-mixed with 7.2 mLof desired concentration of CaCl2 solution (20 or 50%) and placedin an air tight polythene bag for moisture equilibration for 1 h. Afterthis equilibration time, 7.2 mL of NaOH solution of desired con-centration (14.6 or 36.4%) was mixed with expansive soil and

compacted to a dry density of 1:45 Mg∕m3 using a hand-operatedstatic press. Compacted specimens were placed in desiccators formoisture equilibration for 24 h. After this equilibration time, thecompacted soil specimens (w ¼ 25%) were placed between twooven-dried porous stones with oven-dried filter papers and wereset up in the fixed ring oedometer assembly. A nominal seating loadof 6.25 kPa was applied, and the specimens were inundated withdistilled water for swell potential determination. These oedometerswell tests are designated as Tests 1 and 2, respectively (Table 3).

Similar oedometer swell potential tests were also conductedwith expansive soil specimens remolded with 7.2 mL of NaOH sol-ution (14.6 or 36.4%) and placed in an air tight polythene bagfor moisture equilibration for 1 h. After this equilibration time,7.2 mL of CaCl2 solution of desired concentration (20 or 50%)was mixed with expansive soil and compacted to a dry density of1:45 Mg∕m3 using a hand-operated static press. Compacted spec-imens (w ¼ 25%) were placed in desiccators for moisture equili-bration for 24 h. These specimens were inundated with distilledwater at a seating load of 6.25 kPa for swell potential determina-tion. These oedometer swell tests are designated as Tests 3 and 4,respectively. Table 3 shows the details of swell potential tests.

Table 3 also shows the calculated amount of lime precipitationin the soil and the percentage of lime precipitation by dry weight ofsoil. The amount of lime precipitated when 7.2 mL of 20% CaCl2solution and 7.2 mL of 14.6% NaOH solution are mixed sequen-tially with the expansive soil may be calculated as

74110

×20100

× 7:2 ¼ 0:97 g ð3Þ

Unconfined Compressive Strength Tests

All UCS test specimens were of 38-mm diameter and 76-mmlength, which needed 125 g of expansive soil by dry weight

Table 2. Details of Liquid Limit and Plastic Limit Tests

Series designationPercentage of solution concentration

on weight basis (%)aCalculated amount oflime precipitation (g)

Calculated percentageof lime precipitation bydry weight of soil (%)

Liquidlimit (%)

Series 1: CaCl2 þ NaOH 10% CaCl2; 7.3% NaOH 3.03 2.5 60

20% CaCl2; 14.6% NaOH 6.05 5.0 58

35% CaCl2; 25.5% NaOH 10.59 8.8 55

50% CaCl2; 36.4% NaOH 15.14 12.6 43

65% CaCl2; 47.3% NaOH 19.68 16.4 43

Series 2: CaCl2 þ NaOH 7.3% NaOH; 10% CaCl2 3.03 2.5 55

14.6% NaOH; 20% CaCl2 6.05 5.0 50

25.5% NaOH; 35% CaCl2 10.59 8.8 52

36.4% NaOH; 50% CaCl2 15.14 12.6 48

47.3% NaOH; 65% CaCl2 19.68 16.4 50aVolume of solution mixed = 45 mL.

Table 3. Details of Oedometer Tests with Test Designation

Series designationTest

designationPercentage of solution concentration

on weight basisa (%)Calculated amount oflime precipitation (g)

Calculated percentageof lime precipitation bydry weight of soil (%)

Swellpotential

(%)

Series 1: CaCl2 þ NaOH Test 1 20% CaCl2, 14.6% NaOH 0.97 1.7 0.0

Test 2 50% CaCl2, 36.4% NaOH 2.42 4.2 0.0

Series 2: NaOHþ CaCl2 Test 3 14.6% NaOH, 20% CaCl2 0.97 1.7 0.0

Test 4 36.4% NaOH, 50% CaCl2 2.42 4.2 0.0aVolume of solution mixed = 10.25 mL.


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(dry density ¼ 1:45 Mg∕m3). A total of 125 g of expansive soilpassing 2 mmwas mixed with 15.6 mL of CaCl2 solution of desiredconcentration (10, 20, 35, 50 or 65%) and placed in an air tightpolythene bag for moisture equilibration for 1 h. After this equili-bration time, 15.6 mL of NaOH solution of desired concentration(7.3, 14.6, 25.5, 36.4 or 47.3%) was mixed with expansive soiland placed in desiccators for moisture equilibration for 24 h. Themoisture-equilibrated specimens were statically compacted to adry density of 1:45 Mg∕m3 using a hand-operated static press. TheUCS tests performed with this sequence of mixing CaCl2 andNaOH solutions with expansive soil are referred to as Series 1experiments.

In Series 2 experiments, 15.6 mL of NaOH solution of desiredconcentration (7.3, 14.6, 25.5, 36.4 or 47.3%) was mixed with ex-pansive soil and placed in a desiccator for moisture equilibrationfor 1 h. After 1 h equilibration time, 15.6 mL of CaCl2 solutionof desired concentration (10, 20, 35, 50 or 65%) was mixed withexpansive soil and placed in a desiccator for moisture equilibrationfor 24 h. The moisture-equilibrated specimens were statically com-pacted to a dry density of 1:45 Mg∕m3 using a hand-operated staticpress. The UCS tests performed with this sequence of mixingNaOH and CaCl2 solutions with expansive soil are referred to asSeries 2 experiments. Both series of UCS tests were conducted at astrain rate of 0:8%∕min. Table 4 shows the details of the specimensprepared by mixing expansive soil with CaCl2 and NaOH solutionsin two different sequences. Table 4 also shows the calculatedamount of lime precipitation in the soil and the percentage of limeprecipitation by dry weight of soil. Calculation of the amount oflime precipitation in the soil and the percentage of lime precipita-tion is discussed in the “Index Properties” section.

Few additional specimens were prepared to study the effectof curing on the UCS of the expansive soil. The compacted spec-imens were also cured for 7 and 21 days in a dessicator. At the end

of 7 and 21 days curing period, the UCS was determined to bringout the effect of sequential mixing of CaCl2 and NaOH solutions intwo different sequences (Series 1 and 2).

Results and Discussions

Index Properties

Fig. 1 shows the variations in liquid limit and soil pH with the cal-culated percentage of lime precipitation on sequential mixing ofexpansive soil with CaCl2 and NaOH solutions in two different se-quences. The liquid limit decreased as the calculated percentage oflime precipitation increased up to 12.6 and 5% in Series 1 and 2specimens, respectively, and further lime precipitation did not alterthe liquid limit significantly (Fig. 1). At a lime precipitation per-centage of 12.6 and 5% in Series 1 and 2 specimens, the liquid limitnotably reduced from 75% to 43 and 50%, respectively.

The variations in plasticity index and soil pH with the calculatedpercentage of lime precipitation on sequential mixing of expansivesoil with CaCl2 and NaOH solutions in two different sequencesare shown in Fig. 2. The plasticity index of Series 1 and 2 spec-imens at a lime precipitation percentage of 12.6 and 5% decreasedfrom 50% to 8 and 17%, respectively (Fig. 2). Figs. 1 and 2 alsoshow that the pH of expansive soil increased to 12 at an approx-imately 5% calculated percentage of lime precipitation for bothSeries 1 and 2 specimens, which is conducive for the pozzolanicreactions to occur.

The Atterberg limits of the Series 1 and 2 specimens were de-termined after a 24-h curing period. Although the pH of these soils(12) is conducive for pozzolanic reactions to occur, the curingperiod (24 h) is insufficient; earlier studies indicate that curingperiods > 7 days (at room temperature) facilitate a substantial

Table 4. Details of Unconfined Compressive Tests

SeriesPercentage of solution concentration

on weight basisa (%)Calculated amount oflime precipitation (g)

Calculated percentage oflime precipitation by dry

weight of soil (%)

Unconfinedcompressivestrength (kPa)

Series 1: CaCl2 þ NaOH 10% CaCl2, 7.3% NaOH 1.05 0.8 241

20% CaCl2, 14.6% NaOH 2.10 1.7 505

35% CaCl2, 25.5% NaOH 3.67 2.9 552

50% CaCl2, 36.4% NaOH 5.25 4.2 841

65% CaCl2, 47.3% NaOH 6.82 5.5 664

Series 2: NaOHþ CaCl2 7.3% NaOH, 10% CaCl2 1.05 0.8 166

14.6% NaOH, 20% CaCl2 2.10 1.7 169

25.5% NaOH, 35% CaCl2 3.67 2.9 272

36.4% NaOH, 50% CaCl2 5.25 4.2 164

47.3% NaOH, 65% CaCl2 6.82 5.5 494aVolume of solution mixed = 15.6 mL.

Table 5. pH and Pore Salinity Values of Series 1 and 2 Unconfined Compressive Test Specimens

SeriesPercentage of solution concentration

on weight basis (%)

pH Pore salinity (mg∕L)

1 day 7 days 14 days 21 days 1 day 7 days 14 days 21 days

Series 1: CaCl2 þ NaOH 20% CaCl2, 14.6% NaOH 10.73 10.76 10.83 10.76 763 821 833 859

35% CaCl2, 25.5% NaOH 11.47 — 11.46 11.42 1,224 — 1,244 1,686

50% CaCl2, 36.4% NaOH 11.73 11.76 11.82 11.78 1,558 1,583 1,878 2,173

Series 2: NaOHþ CaCl2 14.6% NaOH, 20% CaCl2 11.00 10.99 11.00 10.74 788 1,051 1,058 1,096

25.5% NaOH, 35% CaCl2 11.57 11.60 11.65 11.37 1,109 1,795 1,865 1,897

36.4% NaOH, 50% CaCl2 11.63 11.62 11.65 11.63 1,301 1,795 1,865 2,071


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degree of pozzolanic reactions (Prakash et al. 1989; Bell 1988a).The significant reduction in liquid limit and plasticity index of ex-pansive soil on sequential mixing of CaCl2 and NaOH solutionswith expansive soil is primarily attributed to strong short-termlime-modification reactions involving replacement of native mono-valent exchangeable cations by divalent calcium ions (source ofcalcium is added CaCl2 solution). The addition of CaCl2 and NaOHsolutions would also increase the pore water salinity, which in turnwould act to suppress the diffuse ion layer and liquid limit values(Yong and Warkentin 1975; Mitchell 1993; Sridharan et al. 1986).

Oedometer Swell Potential

Fig. 3 compares the time-swell plots of Test 1 specimen and Test 2specimen with untreated soil specimen. Fig. 4 compares the time-swell plots of Test 3 specimen and Test 4 specimen with untreatedsoil specimen. The Test 1, Test 2, Test 3, and Test 4 specimens donot swell (swell potential ¼ 0%); in comparison, the untreated soilexhibits swell potential of 4.95%. The oedometer swell potentialsof the Test 1 to Test 4 specimens were determined after 24 h ofcuring period. The significant reduction in the oedometer swell po-tential of expansive soil specimens on sequential mixing of CaCl2

and NaOH solutions is again primarily attributed to strong short-term lime-modification reactions and an increase in pore watersalinity. As subsequently discussed, the reductions in plasticity in-dex and odeometer swell potentials are also likely to be contributedby poorly formed cementation products that appear during earlystages of curing.

Unconfined Compressive Strength

Fig. 5 shows the variation of UCS with the calculated percentage oflime precipitation on sequential mixing of expansive soil withCaCl2 and NaOH solutions in two different sequences. The UCSincreased as the calculated percentage of lime precipitation in-creased up to 4.2%, and further lime precipitation slightly reducedthe UCS of Series 1 specimen. Interestingly, the compressivestrength of Series 2 specimen is nearly constant up to 4.2% limeprecipitation and thereafter increases to 494 kPa at 5.5% lime pre-cipitation. Fig. 5 also shows that the pH of the Series 1 and 2 spec-imens increases to 10.73–11.00 at 1.7% lime precipitation andreaches a maximum (11.63–11.73) at 4.2% lime precipitation.At these pH levels, alumina and silica dissolve from clay latticeand combine with calcium ions to form CSH and CAH, which ce-ment the clay particles together, leading to an increase in strength(Eades and Grim 1960; Wang et al. 1963; Diamond et al. 1963;Rajasekaran and Narasimha Rao 1998; Boardman et al. 2001).The Series 1 and 2 specimens shown in Fig. 5 were cured for

7

8

9

10

11

12

13

14

40

50

60

70

80

0 5 10 15 20

pH

Liq

uid

lim

it (

%)

Lime precipitation (%)

Series 1:LLSeries 2: LLSeries 1: pHSeries 2: pH

Fig. 1.Variations of liquid limit and soil pH with calculated percentageof lime precipitation on sequential mixing of expansive soil withcalcium chloride (CaCl2) and sodium hydroxide (NaOH) solutionsin two different sequences (Series 1 and 2)

7

8

9

10

11

12

13

14

0

20

40

60

0 5 10 15 20

pH

Plas

ticity

inde

x (%

)


Series 1: PISeries 2: PISeries 1: pHSeries 2: pH

Fig. 2. Variations of plasticity index and soil pH with calculatedpercentage of lime precipitation on sequential mixing of expansivesoil with calcium chloride (CaCl2) and sodium hydroxide (NaOH)solutions in two different sequences (Series 1 and 2)

0

1

2

3

4

5

6

0.1 1 10 100 1000 10000

Swel

l (%

)

Time (min)

Untreated

Test 1

Test 2

Fig. 3. Time-swell plots of untreated, Test 1, and Test 2 specimens

0

1

2

3

4

5

6

0.1 1 10 100 1000 10000

Swel

l (%

)

Time (min)

UntreatedTest 3Test 4

Fig. 4. Time-swell plots of untreated, Test 3, and Test 4 specimens


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24 h. According to Bell (1988a), the compressive strength devel-oped at early stages of curing is contributed by poorly formedcementation products.

At any given lime precipitation content, Series 1 specimensare characterized with higher UCS than Series 2 specimens. Forexample, at lime precipitation of 1.7%, the UCS of Series 1 speci-men is 505 kPa, whereas the UCS of Series 2 specimen is 169 kPa.The UCS test results also indicate that mixing CaCl2 and NaOHsolutions sequentially with expansive soils (Series 1 specimens)is preferred over mixing NaOH and CaCl2 solutions (Series 2specimens).

Effect of Curing Period on Unconfined CompressiveStrength

The effect of curing period on the UCS developed by the com-pacted expansive soil specimens subjected to lime precipitation isdiscussed in this section. As mentioned previously, theoretically,1.7% of lime is precipitated by mixing expansive soil sequentiallywith 20% CaCl2 and 14.6% NaOH solutions. Similarly, 4.2% oflime is precipitated by mixing expansive soil sequentially with50% CaCl2 and 36.4% NaOH solutions. Because the ICL for theexpansive soil is 2.5%, calculated lime precipitation contents of1.7% (less than ICL) and 4.2% (greater than ICL) are chosen.

Fig. 6 shows the variation in UCS with curing period for com-pacted expansive soil specimens subjected to 1.7% lime precipita-tion. Fig. 7 shows the variation in UCS strength with curing periodfor compacted expansive soil specimens subjected to 4.2% limeprecipitation. The 1.7% lime-precipitated Series 1 specimensdeveloped compressive strength of 430 and 509 kPa after 1 and21 days of curing period, respectively (Fig. 6). Comparatively,the 1.7% lime-precipitated Series 2 specimens developed com-pressive strength of 169 and 268 kPa after 1 and 21 days ofcuring period, respectively (Fig. 6). The data in Fig. 7 show that4.2% lime-precipitated Series 1 specimens developed compressivestrength of 841 and 1,188 kPa, whereas Series 2 specimens devel-oped compressive strength of 164 and 656 kPa after 1 and 21 daysof curing period, respectively. The trends of the results in Figs. 6and 7 indicate that lime-precipitated specimens gain anywhere from18–41 and 58–300% increase in compressive strength on increas-ing the curing period from 1 to 21 days for Series 1 and 2 spec-imens, respectively. The results bring out the role of crystallizationof cementation products in strength gain.

Figs. 6 and 7 also show the variation in soil pH withcuring period which increased to 10.73–11.00 on mixing

20%CaCl2 and 14:6%NaOH solutions and 11.62–11.82 on mix-ing 50%CaCl2 and 36:4%NaOH solutions. It is known that long-term pozzolanic reactions are favored at soil pH ≥ 12 (Eades andGrim 1960; Diamond et al. 1963; Rogers et al. 1997). The soil pHvalues of the sequentially mixed specimens are< 12 (Figs. 6 and 7;Table 5). To examine the possible contribution of pozzolanic reac-tions to soil strength, the compressive strengths of lime pile–treatedspecimens (data from Thyagaraj 2001; Table 7) are compared withthis study (Figs. 6 and 7). Thyagaraj (2001) had observed that thelime pile technique led to minor increase in pH (from 8 to 8.4) thatwas not conducive for promotion of pozzolanic reactions and there-fore did not alter the compressive strength. Sequential mixing of thesoil, however, led to 239–835 and 29–417% (1–21 days cured) in-creases in compressive strengths for Series 1 and 2 specimens, re-spectively. The much larger strengths developed by the sequentiallymixed specimens indicate that in addition to modification reactions,pozzolanic reactions have also occurred. However, the inability ofthe technique to mobilize pH values ≥ 12 could have restrained thecomplete realization of the pozzolanic reactions that would haveled to even larger strengths. According to Boardman et al. (2001),initiation of dissolution of silica and alumina in clay lattice occursat pH of approximately 9–10, which explains the occurrence

7.0

7.5

8.0

8.5

9.0

9.5

10.0

10.5

11.0

11.5

12.0

0

200

400

600

800

1000

0 2 4 6

pH

Unc

onfi

ned

com

pres

sive

str

engt

h (k

Pa)


Series 1: UCSSeries 2: UCSSeries 1: pHSeries 2: pH

Fig. 5. Variations of unconfined compressive strength and soil pH withcalculated percentage of lime precipitation on sequential mixing ofexpansive soil with calcium chloride (CaCl2) and sodium hydroxide(NaOH) solutions in two different sequences (Series 1 and 2)

10.1

10.3

10.5

10.7

10.9

11.1

0

100

200

300

400

500

600

0 5 10 15 20 25

pH

Unc

onfi

ned

com

pres

sive

str

engt

h (k

Pa)

Curing period (days)


Fig. 6. Variations of unconfined compressive strength and soil pH withcuring period for compacted expansive soil mixed with 20% calciumchloride (CaCl2) solution and 14.6% sodium hydroxide (NaOH)solution in two different sequences (1.7% lime precipitation)

11.0

11.2

11.4

11.6

11.8

0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25

pH

Unc

onfi

ned

com

pres

sive

str

engt

h (k

Pa)

Curing period (days)


Fig. 7. Variations of unconfined compressive strength and soil pH withcuring period for compacted expansive soil mixed with 50% calciumchloride (CaCl2) solution and 36.4% sodium hydroxide (NaOH)solution in two different sequences (4.2% lime precipitation)


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of pozzolanic reactions in the sequentially treated specimens.Figs. 6 and 7 also show that UCS of Series 1 specimens is higherin comparison with Series 2 specimens at all the curing periods.

Comparison of Lime Precipitation Technique withOther Techniques

Table 6 shows a comparison of the index properties of expansivesoil specimens directly mixed with lime and subjected to limeprecipitation. Data in Table 6 show that both methods are equallyeffective in reducing the liquid limit and plasticity index of theexpansive soil.

Table 7 shows a comparison of the properties of expansive soilspecimens treated with lime pile technique (Thyagaraj 2001) andlime precipitation technique. Thyagaraj (2001) reported that thelime pile treatment increased the soil pH and pore salinity to8.40 and 517 mg∕L from untreated values of 8.00 and 244 mg∕L,respectively (Table 7). The swell potential of lime pile–treatedspecimen reduced to 0.4% from 2.1%, whereas the lime precipita-tion technique reduced the swell potential to 0% from untreatedvalue of 4.95%. The pH of lime pile–treated soil (8.4) was notconducive for the pozzolanic reactions to occur, and as a result,the compressive strength of lime pile–treated specimens was unaf-fected (Table 7). Comparatively, the lime precipitation techniqueincreased the soil pH to 11.62–11.76 (7 days, cured), which is pre-sumably conducive for pozzolanic reactions to occur. Therefore,the UCS of lime precipitation technique–treated specimens in-creased to 619–895 kPa (7 days, cured) from an untreated valueof 127 kPa (Table 7). The greater efficiency of lime precipitation

technique in improving the compressive strength of the expansivesoil shows its superiority over the lime pile technique.

Table 7 also shows a comparison of the properties of expan-sive soil specimens treated with lime slurry technique (Rao andThyagaraj 2003) and lime precipitation technique. Both techniquescould raise the pH of soil (11.62–11.95, Table 7) to levels thatare conducive for the pozzolanic reactions to occur (Boardmanet al. 2001). The swell potential of lime slurry–treated specimenreduced to 0% from an untreated value of 1.4%, whereas the limeprecipitation technique reduced the swell potential to 0% from anuntreated value of 4.95%. The UCS of 10 days, cured lime slurry–treated specimens increased to 113 from 77 kPa. Comparatively,the lime precipitation technique increased the UCS of 7 days, curedspecimens to 619–895 from 127 kPa (untreated value). This showsthat both methods could promote the soil-lime pozzolanic reac-tions. However, the higher strengths exhibited by the lime precipi-tation technique–treated specimens are attributed to flocculation ofclay particles owing to lime precipitation in addition to pozzolanicreactions.

Practical Significance

Sequential mixing of CaCl2 and NaOH solutions with expansivesoil resulted in precipitation of lime. The precipitated lime couldpromote strong lime-modification reactions and strong soil-limepozzolanic reactions. The lime-modification reactions togetherwith the poorly developed cementation products controlled the

Table 6. Comparison of Index Properties of Expansive Soil Specimens Directly Mixed with Lime and Subjected to Lime Precipitation

Calculated percentage oflime precipitation (%)

Percentage of solutionconcentrationa (%)

Series 1: CaCl2 þ NaOH Series 2: NaOHþ CaCl2 Directly mixed with lime

wL (%) wP (%) IP (%) wL (%) wP (%) IP (%) Lime (%) wL (%) wP (%) IP (%)

2.5 10% CaCl2, 7.3% NaOH 60 32 28 55 33 22 2 63 36 27

5.0 20% CaCl2, 14.6% NaOH 58 36 22 50 33 17 4 57 37 20

8.8 35% CaCl2, 25.5% NaOH 55 35 20 52 34 18 6 52 37 15

12.6 50% CaCl2, 36.4% NaOH 43 35 8 48 31 17 8 50 37 13

16.4 65% CaCl2, 47.3% NaOH 43 32 11 50 32 18 10 48 37 11

Note: wL = liquid limit; wP = plastic limit; IP = plasticity index.aVolume of solution mixed = 45 mL.

Table 7. Comparison of Properties of Expansive Soil Specimens Treated with Lime Pile, Lime Slurry, and Lime Precipitation Techniques

Source Treatment

Percentageof lime(%)

Radialdistance/series

Curingperiod(days) pH

Pore salinity(mg∕L) wL (%) wP (%) IP (%)

Swellpotentiala

(%)

Unconfinedcompressivestrength(kPa)a

Thyagaraj

(2001)

Lime pile

treated

5.5 1.5d 10 8.40 (8.00) 517 (244) 93 (95) 26 (24) 67 (71) 0.4 (2.1) 68 (68)

Rao and

Thyagaraj

(2003)

Lime slurry

treated

6 1.5d 10 11.95 (8.00) 1,436 (244) 86 (95) 44 (24) 42 (71) 0.0 (1.4) 113 (77)

This

investigation

Untreated – – – 8.00 340 75b 25b 50b 4.95c 127

Lime

precipitation

treated

4.2 Series 1:

CaCl2 þ NaOH

1 11.73 1,558 58b 36b 22b 0.0c 841

7 11.76 1,583 – – – – 895

Series 2:

NaOHþ CaCl2

1 11.63 1,301 50b 33b 17b 0.0c 164

7 11.62 1,795 – – – – 619

Note: Values in the parenthesis are of untreated specimen; d = diameter of hole for lime pile or lime slurry injection.aSwell potential and unconfined compressive strength of untreated specimens were determined at moisture content and dry densities similar to those of treatedspecimens.bAtterberg limits were determined with 5% lime precipitation.cSwell potentials were determined with 3.4% lime precipitation.


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swelling potential, reduced the plasticity index, and increased theUCS of the expansive clay as the specimens were cured for 24 h.Comparatively, both lime-modification and well-developed crystal-line cementation products contributed to the marked increase inthe UCS strength of the expansive soil that was cured for periodsof 7–21 days. However, further investigation is needed for exam-ining the efficacy of lime precipitation technique in stabilizing thein situ expansive soils by sequential permeation of CaCl2 andNaOH solutions into the in situ soil, either through ponding orboreholes.

The amount of lime precipitation in the soil should be greaterthan the ICL value, because the amount of lime precipitation inexcess of the ICL value is used in the cementation process only.The ICL values for most of the expansive soils range from 3–8%.The amount of lime precipitation can be increased either by increas-ing the concentration of CaCl2 and NaOH solutions used for per-meation or by increasing the volume of CaCl2 and NaOH solutions.

This method of stabilization may prove to be advantageous overthe other techniques in the following conditions:• Stabilization of expansive soils below the existing structures

on which lime piles construction is not possible because ofthe existing structures. In such a situation, boreholes have tobe made along the periphery of existing structures with requiredspacing. These boreholes have to be filled with coarse sand, andCaCl2 and NaOH solutions are sequentially permeated for the insitu precipitation of lime below the existing structures. Thismethod of stabilization will be far superior to the lime pile tech-nique owing to the very high solubility and diffusion rates ofCaCl2 and NaOH solutions in water in contrast to the solubilityand diffusion rates of lime.

• In stiff to very stiff expansive soils, it is very difficult to formlime columns in situ. In such a situation, in situ lime precipita-tion through boreholes may prove to be the most effective andviable method of stabilization.

• This technique will have an added advantage in a site contami-nated with NaOH solution. In such a case, CaCl2 solution aloneneeds to be permeated through the contaminated soils for in situprecipitation of lime and, thus, stabilization of the contami-nated soil.

Conclusions

The efficacy of lime precipitation technique in stabilizing an expan-sive soil is examined through laboratory investigation. Precipitationof lime is achieved by sequential mixing of expansive soil withCaCl2 and NaOH solutions in two different sequences. The follow-ing conclusions are drawn from this investigation:1. Sequential mixing of CaCl2 þ NaOH or NaOHþ CaCl2 solu-

tions with expansive soil led to drastic reduction in the liquidlimit and plasticity index of expansive soil. The considerablereduction in the liquid limit and plasticity index of the expan-sive soil is primarily attributed to strong short-term lime-modification reactions occurring between precipitated limeand the soil.

2. The swell potential of the expansive soil specimens reducedto 0% from untreated value of 4.95% as a consequence of thestrong lime-modification reactions and poorly developed ce-mentation products formed during early stages of curing inthe treated soil.

3. The UCS increased as the percentage of lime precipitation in-creased in both sequences of mixing expansive soil with CaCl2and NaOH solutions. The lime-modification reactions togetherwith the poorly developed cementation products increased

the UCS of the expansive soil specimens cured for 24 h.The marked increase in UCS exhibited by 7–21 days’ curedexpansive soil specimens is apparently a consequence of lime-modification reactions and well-developed crystalline cemen-tation products formed in the treated specimens.

4. Atterberg limits and UCS results show that the sequential mix-ing of expansive soil with CaCl2 solution followed by NaOHsolution is more effective than mixing expansive soil withNaOH solution followed by CaCl2 solution.

References

Bell, F. G. (1988a). “Stabilisation and treatment of clay soils with lime.Part 1: Basic principles.” Ground Eng., 21(1), 10–15.

Bell, F. G. (1988b). “Stabilisation and treatment of clay soils with lime.Part 2: Some applications.” Ground Eng., 21(2), 22–30.

Boardman, D. I., Glendinning, S., and Rogers, C. D. F. (2001).“Development of stabilisation and solidification in lime-clay mixes.”Geotechnique, 50(6), 533–543.

British Standards Institution (BSI). (1990). “Method of test for stabilizedsoils.” BS 1924, Milton Keynes, U.K.

Broms, B. B., and Boman, P. (1975). “Lime-stabilized columns.” Proc., 5thAsian Regional Conf. on Soil Mechanics and Foundation Engineering,Vol. 1, INSDOC Regional Centre, Bangalore, India, 227–234.

Bureau of Indian Standards. (1972). “Methods of test for soils: Determi-nation of shrinkage factors (first revision).” IS 2720 (Part 6), New Delhi,India.

Bureau of Indian Standards. (1980a). “Methods of test for soils: Determi-nation of specific gravity. Section 1: Fine grained soils (First revision).”IS 2720 (Part 3), New Delhi, India.

Bureau of Indian Standards. (1980b). “Methods of test for soils: Determi-nation of water content-dry density relation using light compaction(second revision).” IS 2720 (Part 7), New Delhi, India.

Bureau of Indian Standards. (1985a). “Methods of test for soils: Grain sizeanalysis (second revision).” IS 2720 (Part 4), New Delhi, India.

Bureau of Indian Standards. (1985b). “Methods of test for soils: Determi-nation of liquid limit and plastic limit (second revision).” IS 2720,(Part 5), New Delhi, India.

Chen, F. H. (1988). Foundations on expansive soils, Elsevier, New York.Chew, H. H., Talkeda, T., Ichikawa, K., and Hosoi, T. (1993). “Chemico

lime pile soil improvement used for soft clay ground.” Proc., 11thSouth East Asian Geotechnical Conf., Singapore, 319–324.

Diamond, S., White, J. L., and Dolch, W. L. (1963). “Transformation ofclay mineral by calcium hydroxide attack.” Proc., 12th National Conf.on Clays and Clay Minerals, E. Ingerson and W. K. Brakely, eds.,Clay Mineral Society, Chantilly, VA, 359–379.

Eades, J. L., and Grim, R. E. (1960). “The reaction of hydrated lime withpure clay minerals in soil stabilization.” Highw. Res. Board, Bull., 262,51–63.

Glendinning, S., and Rogers, C. P. F. (1996). “Deep stabilisation usinglime.” Proc., Seminar on Lime Stabilization, Loughborough Univ.,Thomas Telford, London, 127–136.

Holm, G., Bredenberg, H., and Broms, B. B. (1981). “Lime columns asfoundation for light structures.” Proc. 10th Int. Conf., Soil Mechanicsand Foundation Eng., Vol. 3, A. A. Balkema, Rotterdam, 687–694.

Mitchell, J. K. (1993). Fundamentals of soil behavior, 2nd Ed., Wiley,New York.

Nelson, J. D., and Miller, D. J. (1992). Expansive soils: Problems and prac-tice in foundation and pavement engineering, Wiley, New York.

Porbaha, A. (1998). “State-of-the-art in deep mixing technology: Part I.Basic concepts and overview.” Ground Improv., 2(2), 81–92.

Prakash, K., Sridharan, A., and Rao, S. M. (1989). “Lime addition and cur-ing effects on the index and compaction characteristics of a montmo-rillonitic soil.” Geotech. Eng., 20(1), 39–47.

Rajasekaran, G., and Narasimha Rao, S. (1998). “X-ray diffraction and mi-crostructural studies of lime-marine clay reaction products.” Geotech.Eng., 29(1), 1–27.

Rao, S. M., and Thyagaraj, T. (2003). “Lime slurry stabilization of anexpansive soil.” Geotech. Eng., 156(3), 139–146.


J. Mater. Civ. Eng., 2012, 24(8): 1067-1075

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from

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rary

.org

by

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10/1

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yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

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ghts

res

erve

d.

http://dx.doi.org/10.1680/geot.2001.51.6.533

Rao, S. M., and Venkataswamy, B. (2002). “Lime pile treatment of blackcotton soils.” Ground Improv., 6(2), 85–93.

Rogers, C. D. F., Glendinning, S., and Holt, C. C. (2000). “Slope stabili-zation using lime piles: A case study.” Ground Improv., 4(4), 165–176.

Rogers, C. D. F., Glendinning, S., and Roff, T. E. J. (1997). “Lime modi-fication of clay soils for construction expediency.” Geotech. Eng.,125(4), 242–249.

Sridharan, A., Rao, S. M., and Murthy, N. S. (1986). “Compressibilitybehaviour of homoionised bentonites.” Geotechnique, 36(4), 551–564.

Thyagaraj, T. (2001). “Laboratory studies on in-situ chemical stabilizationof black cotton soil.” M.Sc. (Engg.) dissertation, Indian Institute ofScience, Bangalore, India.

Tsytovich, N. A., Abelev, M. Yu., and Takhirov, I. G. (1971). “Compactingsaturated loess by means of lime piles.” Proc., 4th Int. Conf. on SoilMechanics and Foundation Engineering, Akademiai Kiado, Budapest,837–842.

Wang, W. T. (1989). “Experimentation of improving soft clay with limecolumn.” Proc., Int. Conf. on Engineering Problems on Regional Soils,International Academic Publishers, Beijing, 477–480.

Wang, J. W. H., Mateos, M., and Davidson, D. T. (1963). “Comparativeeffects of hydraulic, calcitic and dolomitic limes and cement in soilstabilization.” Highw. Res. Board, Bull., 59, 42–54.

Yong, R. N., and Warkentin, B. P. (1975). Soil properties and behaviour,Elsevier, New York.


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http://dx.doi.org/10.1680/geot.1986.36.4.551

laboratory studies on exapnsive lime

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