Moderate to High Plasticity Clay Soils - Portland Cement … · Comparative Performance of Portland Cement and Lime Stabilization of Moderate to High Plasticity Clay Soils by Sankar

Comparative Performance

of Portland Cement and

Lime Stabilization of

Moderate to High Plasticity

Clay Soils

by Sankar Bha t tachar ja and Javed I . Bha t ty

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Portland Cement Association5420 Old Orchard RoadSkokie, Illinois 60077-1083USAPhone: 847.966.6200 Fax: 847.966.9781www.cement.org

Cover Photo: Compressive strength testing of soil-cement specimen. (42345)

This information is copyright protected. PCA grants permission to electronically share this document with other professionalson the condition that no part of the file or document is changed

PCA R&D Serial No. 2435

Abstract: Stabilization, engineering properties, and durability characteristics of clay soils with moderate to highplasticity clay were investigated in the presence of Type I portland cement and hydrated lime. The objective wasto perform a direct comparison on the performances of portland cement and lime. The properties investigatedwere: plasticity indices, unconfined compressive strength, California bearing ratio, strength after vacuumsaturation (to evaluate freeze-thaw performance), mass loss in wet-dry test, and hydraulic conductivity andleaching. In order to make a direct comparison, both cement- and lime-stabilized soils were tested under identicalconditions. In general, for the moderate Plasticity Index (PI) soils, the performance of portland cement-stabilizedsoils was superior to lime in all the characterizations performed. For the high PI soils, performance of lime wasbetter at lower dosage levels (3%). However, once this threshold was crossed at higher dosages (6 and 9%),cement-stabilized soils exhibited superior engineering and durability properties.

Keywords: Atterberg limits, CBR, California bearing ratio, cement, compaction, compressive strength, hydratedlime, hydraulic conductivity, freeze-thaw, leachate, lime, permeability, portland cement, soil, sulfated soil, soil sta-bilization, vacuum saturation, wet-dry.

Reference: Bhattacharja, Sankar, and Bhatty, Javed, Comparative Performance of Portland Cement and Lime inStabilization of Moderate to High Plasticity Clay Soils, RD125, Portland Cement Association, Skokie, Illinois, USA,2003, 26 pages.

Comparative Performance of Portland Cement and Lime Stabilization of Moderate to High Plasticity Clay Soils � RD125

ISBN 0-89312-215-7

© 2003 Portland Cement AssociationAll rights reserved

Comparative Performance of Portland Cementand Lime Stabilization of Moderate to

High Plasticity Clay Soils

by Sankar Bhattacharja and Javed I. Bhatty*

Construction Technology Laboratories, Inc.

Research and Development Bulletin RD125

*Senior Scientist, CTL Construction Technology Laboratories, Inc., 5400 Old Orchard Road, Skokie, IL 60077, [email protected]


TABLE OF CONTENTS

Page

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Test Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Plasticity Index and Shrinkage Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Optimum Moisture Content and Maximum Dry Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Unconfined Compressive Strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

California Bearing Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Vacuum Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Wet-Dry Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Hydraulic Conductivity of Stabilized Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Plasticity Index and Shrinkage Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Optimum Moisture Content and Maximum Dry Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Unconfined Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

California Bearing Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Vacuum Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Wet/Dry Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Hydraulic Conductivity of Stabilized Soils and Leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

RD125 � Comparative Performance of Portland Cement and Lime Stabilization of Moderate to High Plasticity Clay Soils

1

INTRODUCTION

The modification of clay soils to improve their engineeringproperties is well recognized and widely practiced.Through stabilization, the plasticity of soil is reduced, itbecomes more workable, and its compressive strength andload bearing properties are improved. Such improvementsare the result of a number of chemical processes that takeplace in the presence of a stabilizer.

While both portland cement and lime are capable of pro-viding calcium, the primary ingredient necessary for stabi-lizing a clay soil, they differ in their chemical nature, modeof reaction in the presence of water, and the resulting reac-tion products. Based upon the differences involved in theseprocesses, questions can be raised about the ultimate supe-riority of one over the other. This issue has been addressedin the present investigation. In order to make this an unbi-ased comparative study, both portland cement- andhydrated lime-stabilized soils were prepared and testedunder similar conditions.

A good soil stabilizer should provide calcium ions(Ca2+) in sufficient amount so that the monovalent cations,especially Na+, adsorbed on the cleavage surfaces of clayparticles are exchanged resulting in a more workable soilwith reduced plasticity. In a high pH environment, the sol-ubility of silica and alumina is greatly enhanced, which pro-motes pozzolanic reaction to form calcium-silicate-hydrate(C-S-H) and calcium-aluminate-hydrate (C-A-H). Withportland cement, however, C-S-H and C-A-H are formedimmediately upon hydration, and a flocculation processsimilar to that observed for lime-stabilized soil takes placeto produce a soil with improved engineering properties.

Several factors such as plasticity of soil, types andamounts of stabilizers, mixing and compaction methods,curing conditions, etc., affect the performance and durabil-ity of a stabilized soil. These issues had previously beendiscussed at length by the authors in a review article enti-tled “Stabilization of Clay soils By Portland Cement orLime – A Critical Review of Literature” (Bhattacharja,Bhatty, and Todres, 2003). In the present investigation,these factors have been investigated on a laboratory scaleto provide a one-to-one comparison on the performancesof portland cement- and lime-stabilized soils.

MATERIALS

The soils used in the project were acquired from southernCalifornia and Texas. The southern California soil is desig-nated in the text as Cal soil. Two Texas soils were obtainedfrom two separate locations near Dallas and were identi-fied with the assistance of the Texas DOT. These two soilsare designated as Texas 1 and Texas 2. Both Cal and Texas1 soils were procured from locations where no sulfate-related problems were reported and the sulfate contentswere low. The Texas 2 soil was obtained from an areawhere some sulfate-related problems had been reported.However, the sulfate analysis of the soil indicated that theconcentration of soluble sulfate in the soil was less than500 mg/L.

A soil with sulfate content well over this level couldnot be found for this project. In order to achieve an ele-vated sulfate level, Cal soil was spiked with sodium sulfateto raise the sulfate level to approximately 20,000 mg/L.This soil is designated in the text as sulfated Cal. Sodiumsulfate solution was mixed with Cal soil (passing 4.75 mmsieve) such that the water content of the soil remainedabout 15%, which is 3% and 5% below the optimum mois-ture content (OMC) of Cal soil stabilized with portlandcement and lime, respectively. The sulfated soil was kept ina closed container for a minimum of two weeks prior tomixing with stabilizers.

Portland cement, hydrated lime, and Class F fly ashwere used as the stabilizing agents at various dosagelevels. The cement used was a commercially manufacturedType I portland cement. Commercially produced finelyground hydrated lime with 99% passing 75 µm sieve and97% passing 45µm sieve was used as a stabilizer. Class F flyash was used in combination with either cement or lime.

TEST METHODS

Upon procurement, each of the three soils was dried in air,broken into approximately 2 in. (50 mm) pieces, andremixed. Subsequently, the soils were pulverized in acrusher to less than 0.188 in. (4.75 mm) size for testing. Inorder to stabilize these soils, 3%, 6%, and 9% (by weight) ofType I cement and hydrated lime were used. When Class Ffly ash was used in combination with portland cement orlime, fly ash contents were 6 and 12% and the amount ofcement or lime was kept constant at 6%. In order to char-acterize stabilized specimens at different ages, they were


2

placed in two resealable plastic bags and stored in a moistroom (100% RH) at room temperature. The moist roomcuring minimizes any loss of moisture from sample,while the plastic bags prevent any transfer of moisturefrom outside.

Plasticity Index and Shrinkage Limit

Plasticity of as-received and stabilized soils was measuredfollowing the procedure ASTM D 4318, “Standard TestMethod for Liquid Limit, Plastic Limit, and Plasticity Indexof Soils.” The shrinkage limit was also measured followingthe procedure ASTM D 4943, “Standard Test Method forShrinkage Factors of Soils by the Wax Method,” only whenthe stabilized soil was plastic. The shrinkage limit deter-mines the dimensional stability as the moisture level in thespecimen is changed. It is defined as the percent moisturecontent (in reference to oven-dried weight) at which nofurther reduction in volume takes place as the specimenloses moisture. Ideally, the shrinkage limit should behigher than the optimum moisture content. This conditionensures that absorption of further moisture (as determinedby the difference between shrinkage limit and optimummoisture) beyond the optimum moisture content (OMC)by a compacted soil will not cause any swelling, or that, aloss of moisture will not cause any shrinkage.

Optimum Moisture Content andMaximum Dry Density

Optimum moisture content (OMC) at maximum dry den-sity (MDD) was determined for each of the as-receivedsoils without any stabilizers. As this may differ from that ofthe soil containing a stabilizer, the OMC was determinedseparately with each of the stabilizers at 6% dosage level.This was considered applicable to the remaining two stabi-lizer dosages (3% and 9%). While small variations in thestabilizer content may alter the OMC marginally, consider-ing the intrinsic errors involved in preparation and testing,the OMC values obtained at the 6% level were used for 3%and 9% dosage levels. OMC at MDD was determined forsoils compacted using standard compactive effort (Proctortest) as per ASTM D 698, “Test Method for LaboratoryCompaction Characteristics of Soil Using Standard Effort[12,400 ft-lb/ft3 (600 kN-m/m3)]”. Molds with 4 in.(102 mm) internal diameter were used for compaction.

In the case of hydrated lime, the soil samples were “mel-lowed” for 24 hours prior to compaction. When portlandcement was used as stabilizer, the soil was compactedimmediately after mixing with cement and water. Basedupon the practice in the industry, this compaction schedulewas selected for the present investigation.

Unconfined Compressive Strength

The effect on stabilization by the varying dosages of port-land cement and lime on the unconfined compressivestrength (UCS) of Cal and Texas 1 and 2 soils were investi-gated. Three dosages of portland cement and lime wereseparately mixed with the soils at OMC (as determined inthe previous section) and the mixtures were compactedusing standard compactive effort. Upon demolding, thecompacted specimens were stored in the manner describedabove and tested for UCS at various ages.

As mentioned above, portland cement-stabilized soilsamples were compacted immediately after mixing andthose stabilized with lime were compacted 24 hours aftermixing. The samples were tested for UCS at 3, 7, 28, and91 days following the procedure ASTM D 2166, “StandardTest Method for Unconfined Compressive Strength ofCohesive Soil.”

In order to make a comparison between the immediateand delayed compaction with portland cement, Cal soilwas also compacted 24 hours after mixing with cement.UCS of sulfated Cal soil stabilized with both cement andlime was also determined. In addition, sulfated Cal soilwas stabilized with portland cement and lime in combina-tion with 6% Class F fly ash. Fly ash was added to deter-mine what effect, if any, fly ash had in reducing expansionin the sulfated Cal soil.

California Bearing Ratio

California bearing ratio (CBR), both unsoaked and soaked,of all three soils and those stabilized with portland cementand lime was measured following ASTM D 1883,“Standard Test Method for CBR (California Bearing Ratio)of Laboratory-Compacted Soils.” The soils were com-pacted using standard compactive effort at OMC. Portlandcement-stabilized soils were compacted immediately aftermixing, while lime-stabilized soils were delayed 24 hoursbefore compaction. Two stabilizer dosages, 6% and 9%,were used for all three soils and tested at 91 days. Duringthis period, the compacted specimens in CBR molds wereplaced in double resealable plastic bags and stored in amoist room at room temperature.

Sulfated Cal soil was also tested for unsoaked andsoaked CBR. Any subsequent volume expansion was mon-itored while the CBR molds with the specimens weresoaked in water. The sulfated Cal soil samples were stabi-lized with either 6% portland cement or lime and com-pacted at OMC using the standard compactive effort. Theamounts of mix water used were the same as those of thecorresponding stabilizer for the Cal soil. Samples werestored under identical conditions as described above, andCBR of the stabilized sulfated soil was measured at 91days.


3

Vacuum Saturation

The vacuum saturation test was performed based uponASTM C 593, “Standard Specification for Fly Ash andOther Pozzolans for Use with Lime.” This test provides amethod by which to evaluate freeze-thaw durability whenfly ash or other pozzolans are used with lime. The test wascarried out to evaluate the relative performance of cement-and lime-stabilized soils.

Soil samples were compacted at OMC using standardcompactive effort and stored in conditions described ear-lier. The samples were tested at 7 and 91 days. At the endof the curing period, the soil specimens were placed in achamber (as described in the test procedure) and slowlyevacuated over 45 minutes to reach a pressure of 24 in.(610 mm) of Hg. In order to de-air, the specimens were leftat this pressure for 30 minutes. Upon de-airing, water wasintroduced into the chamber, the vacuum was released,and the entire sample was soaked for one hour.Subsequently, the unconfined compressive strength (UCS)was measured (ASTM D 2166) after draining the surfacewater for approximately 2 minutes.

Wet-Dry Test

The wet-dry test was performed on all three soils stabilizedseparately with portland cement and lime. Following com-paction at OMC using standard compactive effort, the sta-bilized soil samples were stored in double resealable plasticbags in a moist room (100% RH) at room temperature. Thewet-dry test was performed at different ages, 7 and 91 daysafter mixing with the stabilizers. The test procedure usedwas a slight modification of ASTM D 559, “Standard TestMethod for Wetting and Drying Compacted Soil-CementMixtures.” In order to make a direct comparison with thelime-stabilized soils, the application of wire scratch brush,as prescribed in the standard test method, was not made inthis test. Specimens stabilized with either portland cementor lime were prepared from soils passing a 0.188 in.(4.75 mm) sieve and tested in exactly the same manner.

With time, many of the specimens started losing sig-nificant weight making the dimension measurementsunreliable. Also, many of the samples failed prior to the12 wet-dry cycles prescribed in the test procedure.

Hydraulic Conductivity of Stabilized Soils

Hydraulic conductivities were measured for all three soilsstabilized separately with different amounts of cement andlime. The soil specimens used for hydraulic conductivitymeasurements were compacted at OMC using the stan-dard compactive effort. While the specimens were in thecompaction mold, a 2.875 in. (73 mm) diameter specimenwas cored out for measurement. A steel sleeve with a2.875 in. (73 mm) internal diameter and sharpened edgewas used for coring. The specimens were placed in tworesealable plastic bags and stored in a moist room at roomtemperature for 35 days. The dimensions of these speci-mens were approximately 4.5 in. (110 mm) long and 2.875in. (73 mm ) in diameter. On the 35th day, measurementsfor hydraulic conductivity were started. The test procedurefollowed was ASTM D 5084, “Standard Test Method forMeasurement of Hydraulic Conductivity of SaturatedPorous Materials Using a Flexible Wall Permeameter.” Thespecimens were saturated using backpressure and thefalling head and rising tailwater method was used tomeasure the hydraulic conductivity.

Measurements were performed for a period of 60 daysor more. In some cases of low permeability samples, a dif-ferential pressure between two ends of specimen was usedto promote flow and shorten testing time. However, thehydraulic gradient used in the measurement was alwaysbelow the limits prescribed in the test method D 5084.Periodically, a sample of effluent liquid was collected andanalyzed for pH and concentrations of calcium, sodium,and potassium ions. The concentrations of these ions in theinfluent water were also measured to compare with thosein the leachate. The cumulative volume of the effluent wasalso monitored during the entire testing period.

RESULTS AND DISCUSSION

The classification and grain size analysis of the as-receivedsoils are presented in Table 1. Table 2 provides informationon Atterberg and shrinkage limits, optimum moisturecontent (OMC), and maximum dry density (MDD). TheOMC and MDD of the soil samples were determinedusing standard compactive effort and are shown in

Gradation (% passing specific sieve size)

AASHTO No. 4 No. 10 No. 40 No. 100 No. 200Soil ID Textural classification soil group (4.75 mm) (2.00 mm) (425 µm) (150 µm) (75 µm)

Cal Sandy clay A-7-6 100 90 89 80 65

Texas 1 Clay A-7-6 100 94 93 91 88

Texas 2 Clay A-7-6 100 97 96 92 86

Table 1. Classification and Grain Size Analysis of As-Received Soils


4

Figure 1. Table 3 includes information on UCS and CBR ofthe as-received soils.

Plasticity Index and Shrinkage Limit

The Plasticity Index of the as-received Cal soil was 25. Inthe presence of 3% portland cement or lime this soilbecame nonplastic at 1 day. Texas 1 soil having a PI of 42,however, remained plastic at 1 day after addition of 3%cement or lime. The change in PI of Texas 1 soil with stabi-lizer dosage and time is shown in Table 4. The valuesshown in Table 4 are samples that remained plastic; 3%cement and lime up to 91 days and 6% cement at 1 day. Atall other dosage levels the Texas 1 soil became nonplastic at28 and 91 days. It is evident that for this highly plastic soil,the addition of 3% stabilizer is not enough to make it non-plastic. However, at higher dosages and prolonged curing,the soil becomes nonplastic in the presence of either stabi-lizer. A substantial increase in shrinkage limit is also evi-dent in the stabilized specimens.

Texas 2 soil had a PI of 37, and 3% lime was adequateto make it nonplastic. The PIs and shrinkage limits forTexas 2 soil stabilized with portland cement are shown inTable 5. At 28 and 91 days, the portland cement-stabilizedsoils were nonplastic and are not included in the table.

The behavior of sulfated Cal soil stabilized with port-land cement and lime differs slightly from the as-receivedCal soil stabilized with the same ingredients. Only 6% and9% stabilizer were used in stabilizing the sulfated Cal soil;their PIs and shrinkage limits are given in Table 6. Cal soilwas nonplastic in the presence of lime or portland cementat 1 day. However, the lime treated sulfated Cal soilremained plastic at 1 day even with 9% lime.

Atterberg limits

Soil ID Liquid limit Plastic limit Plasticity index Shrinkage limit OMC (%) MDD (pcf)

Cal 43 18 25 25 17 100.1

Texas 1 63 21 42 18 25 88.4

Texas 2 61 24 37 20 23 88.1

Table 2. Atterberg and Shrinkage Limits, Optimum Moisture Content (OMC) and Maximum Dry Density (MDD)of the As-Received Soils

110

106

102

98

94

90

100

96

92

88

84

80

100

96

92

88

84

80

10 2015 25 3530

15 2520 30 4035

15 2520 30 4035

Control6% Cement6% Lime



Moisture content, percent dry weight



Texas 1 soil

Cal soil

Texas 2 soil

Dry

de

nsi

ty,

lbs/

cu f

tD

ry d

en

sity

, lb

s/cu

ft

Dry

de

nsi

ty,

lbs/

cu f

t

Soil Strength Unsoaked SoakedID (psi) CBR (%) CBR (%)

Cal 60 8 5

Texas 1 54 12 4

Texas 2 57 10 4

Table 3. Unconfined Compressive Strength and CBRof As-Received Soils

Figure 1. Moisture-density relationship of the as-receivedand stabilized soils.

RD

125 � C

omparative Perform

ance of Portland Cem

ent and Lime Stabilization of M

oderate to High Plasticity C

lay Soils

5

Stabilizer 9%dosage 3% stabilizer 6% stabilizer stabilizer

Specimenage (day) 1 day 7 days 28 days 91 days 1 day 7 days 1 day

LL PL PI SL LL PL PI SL LL PL PI SL LL PL PI SL LL PL PI SL — —

Cement 53 37 16 27 49 37 12 31 49 40 9 32 50 41 9 29 47 40 7 30 NP NP

Lime 48 38 10 35 54 43 11 34 53 44 9 35 54 48 6 36 — NP NP NP NP NP

Table 4. Liquid Limit (LL), Plastic Limit (PL), Plasticity Indices (PI) and Shrinkage Limits (SL) of Stabilized Texas 1 Soil*

Stabilizerdosage 6% stabilizer 9% stabilizer

Specimenage 1 day 7 days 1 day

LL PL PI SL LL PL PI SL —

Cement 48 38 10 33 47 36 11 31 NP

Lime NP

Table 5. Atterberg and Shrinkage Limits of Cement-Stabilized Texas 2 Soil*

Stabilized sulfated Cal Soil

Dosage 1 day 7 days

Sulfated Cal soil Stabilizer (%) LL PL PI SL

LL PL PI SL Cement6

NP NP9

43 16 27 20 Lime6 48 30 18 33 NP

9 51 30 21 30 NP

Table 6. Atterberg and Shrinkage Limits of Sulfated Cal Soil Stabilized with Various Dosages of PortlandCement and Lime

* The stabilized soils turned nonplastic at all other dosages and ages, and are excluded from the table.

* The stabilized soils turned nonplastic at all other dosages and ages, and are excluded from the table.


6

The Atterberg limits of the sulfated Cal soil (given inTable 6) are approximately the same as those of the as-received soil. However, in the presence of 6 and 9% lime, itremained plastic after 1 day. Whereas, with the samedosages of cement, it was nonplastic. This observation maybe attributed to the consumption of calcium released fromlime to form calcium sulfate hydrates. In such a case, cal-cium was not readily available for soil stabilization. A sim-ilar situation may also be applicable to the calcium releasedfrom the hydration of portland cement. As hydration ofcement helps soil to agglomerate and the original Cal soilis a sandy clay, sulfated Cal soil may have became non-plastic in the presence of cement. This behavior may alsohave influenced the strength of the stabilized sulfated soil,which is discussed later.

Optimum Moisture Content andMaximum Dry Density

The moisture-density plots for the three soils stabilizedwith 6% cement or lime are shown in Figure 1. In all threecases, portland cement-stabilized soils exhibited highermaximum dry density than that achieved with lime addi-tion. The OMC and MDD values are also shown in Table 7.

These values were determined at standard compactiveeffort. The average difference between the shrinkage limitand OMC for Texas 1 soil stabilized with either lime orportland cement is 4%. This suggests that, at 3% dosagelevel, the Texas 1 soil stabilized with either cement or limewill have similar dimensional stability. In the case of Texas2 soil with 3% cement, the difference between averageshrinkage limit and OMC is 9%, indicating a higher dimen-sional stability compared to Texas 1 at the same stabilizerdosage level. At all other ages and dosage levels, the soilswere nonplastic. The OMC values used in compacting thesulfated Cal with portland cement and lime were respec-tively the same as those determined for Cal soil at 6%dosage level.

Unconfined Compressive Strength

For all soil-cement combinations, the unconfined compres-sive strength increased at all ages with cement dosages.The strength gain was very pronounced with the Cal soils(PI of 25) when compacted immediately after mixing ascompared to delayed compaction (see Table 8 andFigure 2). It is evident from Table 8 that Texas 1 soil with aPI of 42 also shows a similar trend. The results indicate that

Soil Cal Texas 1 Texas 2

OMC of as-received soil 17% 25% 23%

Cement Lime Cement Lime Cement Lime

Stabilized OMC MDD OMC MDD OMC MDD OMC MDD OMC MDD OMC MDDSoil (6% (%) (pcf) (%) (pcf) (%) (pcf) (%) (pcf) (%) (pcf) (%) (pcf)stabilizer) 18 104.8 20 101.0 26 92.7 31 89.0 23 93.4 23 87.5

Table 7. Optimum Moisture Content at Maximum Dry Density of Three Soils Stabilized with 6% Cement andLime and Compacted with Standard Compactive Effort (ASTM D 698)

Cement 3% 6% 9%

Compaction Immediate 24-hr delay Immediate 24-hr delay Immediate 24-hr delay

Cal soil

Age 1 day 140 psi 50 psi 240 psi 55 psi 385 psi 45 psi

7 175 40 425 80 590 80

28 220 85 440 125 770 115

91 290 55 500 140 1090 150

Texas 1 soil

Age 7 days 90 psi 55 psi 190 psi 60 psi 250 psi 70 psi

91 110 35 280 70 360 75

Table 8. Unconfined Compressive Strength (psi) of Cal and Texas 1 Soils Stabilized with Portland Cement andCompacted at OMC Immediately and 24-Hour Delay After Mixing


7

compaction of cement-stabilized soil immediately aftermixing significantly increases the strength. A similar obser-vation was also made by Christensen [1969] in his investi-gation on the modification of clay soils by cement.

The achievement of stronger material with immediatecompaction can be attributed to the physicochemical phe-nomenon resulting from the hydration of portland cement.Within a short time after mixing portland cement with soil,

the mixture becomes granular due to agglomeration,which primarily results from the hydration of the cementgrains and helps form a network. If the compaction isdelayed, the network is broken during compaction, lead-ing to a weaker mass. However, compaction prior to suchgranulation is more efficient and provides a stable networkwith superior engineering properties. The granular natureof soil particles also makes the compaction inefficient. Thedifference between the UCS of samples compacted imme-diately and those compacted 24-hour after mixingincreases with age and dosage. This is because the UCS ofdelayed compaction specimens remains approximatelyinvariant with respect to dosage of cement and age. Thissuggests that the bonds that were broken during delayedcompaction were never re-established during the timeperiod of 91 days of testing. In all remaining tests, portlandcement-stabilized soils were compacted immediately aftermixing and lime-stabilized soils were compacted 24 hoursafter mixing.

For comparison, the performances of all three soils sta-bilized separately with portland cement and lime andcompacted at OMC using standard compactive effort areshown in Table 9. These results are also shown in Figure 3.The data clearly indicates the superiority of portlandcement addition for Cal soil with moderate plasticity. Forthe high plasticity Texas 1 and 2 soils, the addition of 3%lime provides only a marginally better strength than 3%cement addition. Again, that trend changes drastically at6% and 9% dosages, where portland cement-stabilized

Dosage 3% 6% 9%

Stabilizer Cement Lime Cement Lime Cement Lime

Cal soil

Age 1 day 140 psi 45 psi 240 psi 75 psi 385 psi 55 psi

7 175 95 425 120 590 95

28 220 150 440 175 770 190

91 290 230 500 260 1090 515

Texas 1 soil


7 90 115 190 110 250 90

28 110 150 240 200 330 170

91 110 150 280 320 360 320

Texas 2 soil


7 110 95 200 75 300 100

28 110 120 280 135 320 130

91 110 135 310 180 365 190

Table 9. Unconfined Compressive Strength of Three Soils Stabilized with Three Dosages of Portland Cementand Lime and Compacted at Respective OMC

1200

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071 26 91

Age after stabilization, days

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pres

sive

Stre

ngth

, psi

3%–IC3%–DC

6%–IC6%–DC

9%–IC9%–DC

Figure 2. Unconfined compressive strengths of Cal soil sta-bilized with 3%, 6%, and 9% cement.


8

specimens exhibit significantly better UCS values. Thissuggests that for clay soils with high plasticity, portlandcement is about equivalent to lime at low dosages (3%).However, at higher dosages of 6% to 9%, cement additionproduces a much stronger stabilized product.

It is also noticeable that the cement-stabilized soilsexhibit higher initial UCS values than those stabilized withlime. Cement-stabilized soils (with an exception to Texas

1 and 2 at 3% dosage) also have a higher strength at91 days. However, the rate of increase in UCS between1 and 91 days for lime-stabilized soil suggests that thestrength gain of lime-stabilized soils is very much depend-ent on the pozzolanic reactions.

UCS values of sulfated Cal soils stabilized with port-land cement and lime with and without the combinationwith 6% Class F fly ash are shown in Tables 10 and 10a. It

1400

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00 20 40 60 80 100

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6% Cement6% Lime6% Cement + 6% FA6% Lime + 6% FA6% Cement + 12% FA6% Lime + 12% FA

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00 20 40 60 80 100


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Texas 2 soil

9% Cement9% Lime6% Cement6% Lime3% Cement3% Lime

Figure 3. Unconfined compressive strengths of soils stabilized with various dosages of portland cement and lime. (Note theexpanded ordinate for the stabilized Cal soil.)


9

appears that cement-stabilized sulfated Cal soils areweaker than Cal soil stabilized with the same amount ofcement. Lime-stabilized sulfated Cal soil, on the otherhand, exhibits a slight increase in UCS at 7 days comparedto Cal soil containing the same amount of lime. However,there is no clear difference in behavior for lime-stabilizedsulfated Cal soil at 91 days. The cement-stabilized sulfatedCal soils are obviously stronger than lime-stabilized soil, asobserved earlier for unadulterated Cal soil. In order tomake a comparison, strengths of sulfated Cal soils are alsoshown in Figure 3.

When Class F fly ash is added to cement or lime at twodosages, 6 and 12% by dry mass of soil, for portlandcement, the UCS values remained approximately invariant

with and without the addition of fly ash. For lime, the UCSvalues with and without fly ash are similar althoughslightly higher values are apparent in the presence of flyash. The lime-fly ash combination may have promptedpozzolanic reactions.

It is seen that with identical additions of lime orcement, Cal soil (PI = 25) produces higher strength at allages and additions than both the Texas 1 and 2 soils withPIs of 42 and 37, respectively. Furthermore, within eachsoil, the addition of cement produces higher strengths thanlime. With the three types of soils examined in the presentinvestigation, the cement addition to soils with immediatecompaction produced equal or stronger soils relative tolime stabilization, with strength improvement evidentfrom the early age.

California Bearing Ratio

The CBR values for both unsoaked and soaked stabilizedspecimens were measured at 91 days. The results for allthree soils are given in Table 11 and the typical penetrationvs. stress plots are shown in Figure 4 for two of the soils.

The portland cement-stabilized Cal soils show signifi-cantly higher CBR values than the lime-stabilized Cal soilsat both 6 and 9% dosages. In fact, the soaked CBR valuesare even higher than the unsoaked values for the cement-stabilized Cal soil. On the other hand, the unsoaked andsoaked values for the lime-stabilized Cal soils are almostunchanged.

The cement-stabilized Cal and Texas 1 soils showed anincrease in the soaked CBR value, while that of all lime-sta-bilized soils (with an exception of Texas 1 soil with 9%lime) and only one cement-stabilized Texas 2 was reduced.This increase in soaked CBR values may be attributed to a

Dosage 6% 9%

Stabilizer Cement Lime Cement Lime

Age 7 days 305 psi 145 psi 455 psi 170 psi

91 435 300 540 390

Table 10. UCS of Sulfated Cal Soil Stabilized withCement and Lime

Stabilizer Cement + Fly Ash Lime + Fly Ash

Dosage, % 6 + 6 6 + 12 6 + 6 6 + 12

Age 7 days 360 psi 325 psi 205 psi 185 psi

91 400 390 400 370

Table 10a. UCS of Sulfated Cal Soil Stabilized withCement and Lime in Combination with Two Dosagesof Class F Fly Ash

Stabilizer Unsoaked Soaked Soaked Moisture atSoil ID dosage (%) Stabilizer CBR (%) CBR (%) moisture (%) compaction (%)

6Cement 240 370 19 18

CalLime 130 130 28 20

9Cement 290 460 23 18

Lime 150 140 26 20

6Cement 190 200 24 26

Texas 1Lime 140 120 28 31

9Cement 190 260 23 26

Lime 140 160 25 31

6Cement 130 100 23 23

Texas 2Lime 110 100 30 23

9Cement 220 190 23 23

Lime 160 160 27 23

Table 11. California Bearing Ratio (CBR) at 91 Days for Soils Stabilized with Portland Cement and Lime


10

renewed hydration of the core of the relatively largercement grains, which may take more than 91 days. Anincrease in cement content from 6% to 9% resulted in sig-nificant increase in CBR values of Cal and Texas 2 soils.However, the increase with lime content is small in allcases. The invariance in the unsoaked CBR values with thestabilizer content in Texas 1 soil may stem from its highplasticity.

The moisture contents (column six in Table 11) meas-ured after performing soaked CBR show lower waterabsorption by cement-stabilized soils. A comparisonbetween the moisture contents of the soaked samples andthe OMC of the compacted specimens suggests thatcement-stabilized soils, in most cases, did not absorbwater. On the other hand, lime-stabilized Cal and Texas2 soils absorbed as much as 8% and 7% additional water,

Unsoaked: Cal – 6% cementUnsoaked: Cal – 6% limeSoaked: Cal – 6% cementSoaked: Cal – 6% lime

0.080.0 0.16 0.24Penetration, in. x 10-1

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Unsoaked: Cal – 9% cementUnsoaked: Cal – 9% limeSoaked: Cal – 9% cementSoaked: Cal – 9% lime

Unsoaked: Texas 2 – 6% cementUnsoaked: Texas 2 – 6% limeSoaked: Texas 2 – 6% cementSoaked: Texas 2 – 6% lime

0.080.0 0.16 0.24Penetration, in. x 10-1

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Unsoaked: Texas 2 – 9% cementUnsoaked: Texas 2 – 9% limeSoaked: Texas 2 – 9% cementSoaked: Texas 2 – 9% lime

0.080 0.16 0.24Penetration, in. x 10-1

7500

6000

4500

3000

1500

0

Stre

ss, p

si

Figure 4. Penetration vs. stress plots from the measurements of California Bearing Ratio of Cal and Texas 2 soils stabilizedwith 6 and 9% portland cement and lime.


11

respectively. The loss of water from stabilized Texas 1 spec-imens may be due to high initial moisture content. Thismay be a reason for the superior performance observed forthe cement-stabilized soils in wet-dry and vacuum satura-tion tests (discussed in the forthcoming sections).

It is apparent from Figure 4 that unsoaked cement-sta-bilized Cal soil specimens do not deform until the load ishigh enough; a behavior generally observed for mortarand concrete. However, soaked specimens and lime-stabi-lized Cal soils exhibit behavior that is typical for untreatedsoils (see Figure 4 for stabilized Texas 2 soils). The profilesof the stress as a function of penetration for the Texas 1 soilstabilized with portland cement and lime are similar tothat of the stabilized Texas 2 soils. Even for the two highlyplastic soils, Texas 1 and Texas 2, cement stabilization, ingeneral, has resulted in higher CBR values (both unsoakedand soaked) than those stabilized with lime. This behaviorwas, however, much more pronounced for Cal soil.Consequently, it is apparent that cement-stabilized soils aremechanically stronger and can sustain higher bearingloads than lime-stabilized soils.

It is noticeable that an increase of about 150% insoaked CBR values compared to unsoaked for cement-sta-bilized Cal soil is not present in the case of the two highlyplastic Texas soils. The unsoaked CBR values for all thelime-stabilized soils presented in Table 11 range between110 and 160%. On the other hand, for Cal with a PI of 25,cement-stabilized soils have unsoaked CBR values of 240%and 290%, and those for Texas 1 and 2 range between 130%and 220%. This suggests that cement stabilization signifi-cantly improves the bearing ratio of moderate PI soil. Forhigh PI soils, cement-stabilized soils also have higher bear-ing ratios than the lime-stabilized ones. The dosage of limeused in stabilization appears to have little influence on theCBR results for all three soils used.

The CBR values for sulfated Cal soil stabilized with 6%portland cement and lime are given in Table 12. Thesevalues are comparable to those observed for Cal soil, aspresented in Table 11. Following the measurements ofsoaked CBR, the stabilized sulfated Cal specimens, whilein the molds, were resoaked in water for 4 weeks withoutremoving the surcharge (weighing 10 lbs [4.5 kg]). Duringthis period, calipers were used to monitor any change insample volume. No increase in sample height wasobserved for the cement-stabilized soil. However, an

increase of 0.35% in height was registered in the caliper forthe lime-stabilized sulfated Cal soil. The moisture contentof these specimens was measured at the end of soakingand is reported in column 4 of Table 12.

The amount of water absorbed during this extendedsoaking period appears to be slightly higher for the sul-fated Cal Soil stabilized with portland cement. The reversewas true for all other soils (shown in Table 11) after96 hours of soaking. However, as observed earlier, thesoaked CBR value for cement-stabilized soil is higher thanthe unsoaked CBR value, and those for the lime-stabilizedsoil remained virtually unchanged. It is anticipated that thereduced water content of lime-stabilized sulfated Cal soilstems from the loss of free water due to conversion tohydrates that are responsible for causing expansion.

Vacuum Saturation

The unconfined compressive strength (UCS) values for Calsoil stabilized with portland cement and lime are given inTable 13 and illustrated in Figure 5. It is obvious that a sig-nificant loss of unconfined compressive strength was expe-rienced by most of the samples in the vacuum saturationtest. The unconfined compressive strength of Cal soil sta-bilized with portland cement was significantly higher thanthose of the lime-stabilized soils before vacuum saturation(see Figure 5 and column 4 of Table 13). A similar trend isalso apparent in the UCS measured following the vacuumsaturation test.

Vacuum saturation itself is a severe test, and removingthe water during evacuation step and then forcing waterinto the specimen to saturate it can do significant damage.The UCS measured after vacuum saturation with water isinfluenced significantly by the pore structure and themechanical strength (tensile and compressive strengths) ofthe sample. Pore walls may collapse during rapid removaland subsequent infiltration of water. Therefore, how allthese parameters individually affect the results is not dis-cernable. Both cement- and lime-stabilized soils aredynamic, as the microstructural changes continue throughthe testing period of 7 and 91 days. Consequently, the com-bination of the strength and pore structure at 7-day isexpected to be different from that at 91-day. This combina-tion may have resulted in significant strength loss at 7-daysbut not at 91-days. However, the following inferences can

Stabilizer Unsoaked Soaked Soaked moisture Swelling after 4 weeks(6%) CBR (%) CBR (%) content (%) of soaking (%)

Cement 230 280 28 0

Lime 160 150 22 0.35

Table 12. California Bearing Ratio (CBR) at 91 Days for Sulfated Cal Soil Stabilized with Portland Cement andLime


12

be drawn from the post vacuum saturation UCS data givenin Table 13: (i) portland cement-stabilized Cal soils exhibitsignificantly higher UCS than the lime-stabilized Cal soiland (ii) cement-stabilized soils show both dosage- andtime-dependent improvement in the UCS, while lime-sta-bilized soils mostly show a time-dependent increase andonly a limited influence from the dosage.

The minimal influence of lime content especially atearly ages, and to some extent at later ages, stems from thefact that these engineering properties depend on themechanical strength of the material. The formation of cal-

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0 21 42 63 84

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0 21 42 63 84

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Age after stabilization, days6% CB6% CA9% CB9% CA

6% LB6% LA9% LB9% LA

6% CB6% CA9% CB9% CA


Cal soil

Texas 1 soil

6% CB6% CA9% CB9% CA


400

300

200

100

0

0 21 42 63 84

Com

pres

sive

str

engt

h, p

si


Texas 2 soil

Figure 5. Compressive strength of stabilized soils beforeand after vacuum saturation. (Note the expanded ordinatefor Cal soil).

• CB and LA = before vacuum saturation• CA and LA = after vacuum saturation• Broken lines connect post vacuum saturation strength

data

UCS before vacuum UCS after vacuumStabilizer Age (day) Dosage (%) saturation (psi) saturation (psi)

76 425 125

Cement9 590 200

916 500 325

9 1090 525

76 120 50

Lime9 95 60

916 260 175

9 515 190

Table 13. Unconfined Compressive Strength of Stabilized Cal Soil Before and After Vacuum Saturation


13

cium silicate hydrate (C-S-H) and calcium aluminatehydrate (C-A-H) in both cement and lime-stabilized soilcontributes to strength development. In the case of port-land cement, these hydrates are produced from bothhydration and pozzolanic reactions, and may continue toform for a long time. However, in the case of lime, thesehydrates are formed from pozzolanic reaction alone. Asthis reaction is a relatively slower process compared tohydration of cement, the dependence on dosage is notapparent at early ages. Furthermore, often this dependenceis not very pronounced at later ages because pozzolanicreaction is a through solution process (presence of freewater is needed for this reaction) and the low solubility ofcalcium hydroxide (approximately 1.2 g per liter) controlsthe amount of calcium available in the pore solution.

The UCS values for Texas 1 and Texas 2 soils are givenin Table 14 and also plotted in Figure 5. Although thesesoils have a high PI, the data presented show a trend simi-lar to that discussed above for the Cal soil. The post satu-ration UCS values achieved for all three lime-stabilizedsoils are very similar. While, those for cement-stabilizedsoils relate to the soil plasticity, the strongest being thecement-stabilized Cal soil. Even with these highly plasticsoils, the post saturation UCS values for portland cement-stabilized soils are in most cases superior to those for lime-stabilized soils. This suggests that regardless of the soilplasticity range used in this investigation, the strength ofthe cement-stabilized soils after vacuum saturation isclearly superior to those of the lime-stabilized soils.

Consequently, portland cement-stabilized soils areexpected to be more durable than lime-stabilized soils infreeze-thaw conditions.

Wet-Dry Test

The durability of soil upon repeated wetting and dryingprimarily depends on the pore structure and tensilestrength of the material. Other parameters, such as inter-particle friction and cohesion may also influence the mate-rial loss in this testing. Similar to vacuum saturation test, aswater moves in and out of pore network of the specimenduring wetting and dying, the pore walls experience capil-lary pressure and may collapse. As a result, in the presentinvestigation, stabilized soils suffered from small to signif-icant material loss during the wet-dry testing, and in manycases, disintegrated prior to completion of 12 cycles, asspecified in the test procedure.

The performance of stabilized Cal soil compacted atOMC using standard compactive effort is shown in Figure6. All Cal soil specimens stabilized with either cement orlime lasted 12 cycles of wetting and drying. The dataclearly indicates that portland cement-stabilized soilexhibits superior performance to that compacted withhydrated lime.

Stabilized Texas 1 soil performed poorly as comparedto stabilized Cal soil, and all of its specimens failed prior toreaching the 12th cycle. This inferior performance is

Age Dosage UCS before vacuum UCS after vacuumSoil Stabilizer (day) (%) saturation (psi) saturation (psi)

76 190 70

Cement9 250 110

916 275 125

Texas 19 360 200

76 110 60

Lime9 90 50

916 320 200

9 348 205

76 200 100

Cement9 300 140

916 310 175

Texas 29 365 280

76 75 50

Lime9 100 55

916 180 140

9 190 180

Table 14. Unconfined Compressive Strength of Stabilized Texas 1 and Texas 2 Soils Before and After VacuumSaturation


14

observed with both the stabilizers as shown in Table 15.Comparing with Cal soil, it is apparent that the high PIsoil suffers more severely in the wetting and drying situa-tions. From the data shown in Table 15 it is evident thatincreasing the stabilizer dosage minimizes the degrada-tion, and this is more applicable to portland cement than

lime. By increasing the dosage from 6% to 9%, the numberof cycles to reach failure increased by seven for cement ascompared to two to three for lime. While at the 6% levelboth the stabilizers exhibit similar performances, at the 9%level, superiority of portland cement over lime addition isdiscernable.

45

35

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5

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Number of wet-dry cycles

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6% Cement – 91 days6% Lime – 91 days

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-50 3 6 9 12


Sam

ple

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ght l

oss,

%


Figure 6. Weight loss in wet-dry durability testing of Cal soil stabilized with 6 and 9% portland cement and lime.


15

The data presented for Texas 2 soil stabilized withportland cement and lime show a similar performance asdescribed for Texas 1 soil. This most likely stems from thesimilarity in plasticity of these two soils. It is noticeable inTable 15 that there is little difference in performancebetween 7 and 91 days, regardless of the stabilizer used.This suggests that for high PI soil, contribution of the sta-bilizer dosage is more significant than age. However, theunconfined compressive strength, before and after vacuumsaturation (discussed earlier), improved with time. Thismay be due to the physical parameters that dominate theperformance in these tests. In the compressive strengthtest, specimens are under compressive load, althoughduring vacuum saturation, pore walls of the specimensexperience some tensile force. In the wet-dry test, tensileforce is applied exclusively on the pore walls as watermoves in and out of the pore network.

Both Texas soils, stabilized with 9% cement, distinctlyperformed better than the corresponding lime-stabilizedsoils. As mentioned above, a similar trend was also

observed in the case of Cal soil. The observation of rela-tively better performance for portland cement than limesuggests that although both supply Ca2+ ions, the ingredi-ent necessary for stabilization, the physicochemicalprocesses involved are not entirely similar, and the wet-drydurability is, more than likely, dictated by this difference.

Hydraulic Conductivity of Stabilized Soilsand Leaching

The hydraulic conductivity measurements were performedon three soils stabilized separately with equal dosages ofcement and lime. During the measurements, effluent liquidwas collected periodically for chemical analysis. All threesoils were analyzed for pH and water-soluble calcium,sodium, potassium, and sulfate ions. These data are shownin Table 16. The concentrations of these ions present in theinfluent water are also included in the table. These soilswere compacted at OMC and the measurements startedwhen the specimens were 35 days old.

Testing Stabilizer Percent weight loss at End of the cycleSoil Stabilizer age (day) dosage (%) the end of failing cycle when sample failed

76 52 3

Cement9 55 10

916 45 4

Texas 19 53 11

76 58 4

Lime9 46 7

916 34 3

9 33 5

76 36 2

Cement9 53 10

916 40 3

Texas 29 51 12

76 57 6

Lime9 53 10

916 49 5

9 55 10

Table 15. Performance of Portland Cement and Lime-Stabilized Texas 1 and Texas 2 Soils in Wet-Dry Test

Concentration (mg/L)

Soil Na+ K+ Ca2+ Mg2+ So42– pH

Cal 280 2 40 20 115 8.0

Texas 1 20 1 210 10 170 7.5

Texas 2 10 3 320 10 470 7.9

Influent 10 1 30 — — 6.5

Table 16. Concentration of Water-Soluble Ions from the Three as-Received Soils and the Influent Water Usedfor Hydraulic Conductivity Measurements


16

The hydraulic conductivity plots for the stabilized Calsoils, shown in Figure 7, clearly indicate that the perme-ability of cement-stabilized Cal soils is one to two orders ofmagnitude lower than those of the lime-stabilized Calsoils. Over a particular length of time, due to lower per-meability, the effluent volume from the cement-stabilizedCal soil is significantly less than that from the lime-stabi-lized Cal soil. The closeness in hydraulic conductivityvalues at both cement dosages suggests that the tortuosityor the pore connectivity developed in the stabilized systemis similar. The hydraulic conductivity values for the lime-stabilized Cal soil are different initially, but became similarduring the test. After about forty days, the pozzolanic reac-tion in the 6% lime-stabilized sample may have been ade-quate enough to make the permeability similar to thatachieved with 9% lime.

Stocker [1975] reported that only 0.5% Ca(OH)2 is suf-ficient to produce a unit layer of reaction product and elim-inate swelling. Subsequently, the process becomesdiffusion dependent, as Ca2+ ions have to diffuse throughthe reaction product. As the solubility of calcium hydrox-ide, either formed due to the hydration of portland cementor supplied by the hydrated lime, is low (1.2 g per liter ofwater), Stocker’s observation suggests that by increasingthe stabilizer dosage, the gain in the long-term propertiesmay not be significantly different. Figure 7 shows that atlater ages, the hydraulic conductivities are similar at bothdosage levels. In Cal soil, a sandy clay, the cementing

action from portland cement hydration resulted in signifi-cant reduction in the hydraulic conductivity compared tothose achieved by lime addition.

The hydraulic conductivity results of Texas 1 soil sta-bilized with 3%, 6%, and 9% cement or lime are shown inFigure 8. The behavior observed here is different from thatobserved for the stabilized Cal soil. At the 3% dosage level,the hydraulic conductivities of the cement- or lime-stabi-lized soils are of the same magnitude and relatively high,although cement-stabilized soil is slightly less permeable.At the 6% level, both the cement- and lime-stabilized soilsstart with a similar permeability, and a time-dependentreduction in permeability is exhibited by the lime-stabi-lized soil. At the 9% level, on the other hand, the cement-stabilized soil has a significantly lower permeability. Thisbehavior indicates that at higher cement content, Texas 1soil performs similarly or better than the same dosage oflime. For a highly plastic clay, a higher amount of calciumis necessary for stabilization. It is also known that theamount of Ca(OH)2 generated from hydration of portlandcement is typically 31% of the weight of cement. As aresult, 3% or 6% cement may not have been adequate toreduce the permeability. However, with an increasedcement content, that requirement is satisfied. Furthermore,an additional benefit was provided by the network forma-tion due to the hydration of the cement particles.

The hydraulic conductivity results, shown in Figure 9,for stabilized Texas 2 soil indicate some similarities to those

1E-05

1E-06

1E-07

1E-08

1E-09

1E-10

1E-11

Hyd

raul

ic c

ondu

ctiv

ity, c

m/s

0 20 40 60 80 100

Cal–6% cement

Cal–6% lime

Cal–9% cement

Cal–9% lime

Leaching time, days

Figure 7. Change in hydraulic conductivity with time for Cal soil stabilized with 6% and 9% portland cement and lime.


17

Texas 1–3% cement

Texas 1–6% cement

Texas 1–9% cement

Texas 1–3% lime

Texas 1–6% lime

Texas 1–9% lime

1E-03

1E-04

1E-05

1E-06

1E-07

1E-08

Hyd

raul

ic c

ondu

ctiv

ity, c

m/s

0 20 40 60 80 100

Leaching time, days

Figure 8. Change in hydraulic conductivity with time for Texas 1 soil stabilized with 3%, 6%, and 9% portland cement and lime.

Texas 2–3% cement

Texas 2–6% cement

Texas 2–9% cement

Texas 2–3% lime

Texas 2–6% lime

Texas 2–9% lime

1E-04

1E-05

1E-06

1E-07

1E-08

Hyd

raul

ic c

ondu

ctiv

ity, c

m/s

0 20 40 60 80 100

Leaching tme, days

Figure 9. Change in hydraulic conductivity with time for Texas 2 soil stabilized with 3%, 6%, and 9% portland cement and lime.


18

observed for the stabilized Texas 1 soil. The hydraulic con-ductivities of the soil stabilized with either 3% portlandcement or lime is of the same order of magnitude, and at6% addition, lime-stabilized soil is less permeable thancement-stabilized soil. This behavior changes at a higherdosage level, and at the 9% level, the hydraulic conductiv-ity values are essentially the same for both portlandcement and lime.

The changes in the concentrations of Ca2+ ions in theeffluent during the course of experiments are shown inFigures 10, 11, and 12 for the three soils. The concentrationof Ca2+ ions in the effluent liquid from all lime-stabilizedsoils remained higher than that from cement-stabilizedsoils throughout the testing period. Furthermore, at ahigher lime dosage, the Ca2+ ion concentration in the efflu-ent is elevated and the level is maintained over a longerperiod. On the other hand, the Ca+ ion concentration in the

effluent from cement-stabilized soils does not show muchof a dose dependency. Consequently, the cumulative lossof calcium from the lime-stabilized soils will be higher dueto higher permeability.

The concentration of Na+ and K+ ions in all cases, withthe exception of Cal soil, remained approximately 50 mg/Lor less throughout the testing period. The higher Na+ ionconcentration in leachates from stabilized Cal soil (shownFigure 10) may be attributed to higher Na+ ion concentra-tion (approximately 300 mg/L) in the as-received soil. ThepH of the leachates collected from the stabilized soilsduring testing was approximately 12 in all cases, and noparticular trend with testing time was observed. Thehigher calcium concentration in leachate, particularly fromthe lime-stabilized soils suggests that due to low solubility,a portion of the hydrated lime used for stabilizationremains unreacted and washes out with the effluent liquid.

Ca2+ Cal–6% cement

Ca2+ Cal–9% cement

Na+ Cal–6% cement

Na+ Cal–9% cement

Ca2+ Cal–6% lime

Ca2+ Cal–9% lime

Na+ Cal–6% lime

Na+ Cal–9% lime

1000

800

600

200

400

0

Con

cent

ratio

n of

ions

leac

hate

, ppm

0 20 40 60 80 100

Leaching time, days

Figure 10. Concentration of calcium and sodium ions in leachates collected during measurements from Cal soil stabilizedwith 6% and 9% portland cement and lime.


19

Texas 1–3% cement

Texas 1–6% cement

Texas 1–9% cement

Texas 1–3% lime

Texas 1–6% lime

Texas 1–9% lime

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800

600

400

200

0

Con

cent

ratio

n of

ions

in le

acha

te, p

pm

0 20 40 60 80 100

Leaching time, days

Figure 11. Concentration of calcium ions in leachates collected during measurements from Texas 1 soil stabilized with 3%,6%, and 9% portland cement and lime.

Texas 2–3% cement

Texas 2–6% cement

Texas 2–9% cement

Texas 2–3% lime

Texas 2–6% lime

Texas 2–9% lime

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800

600

400

200

0

Con

cent

ratio

n of

ions

in le

acha

te, p

pm

0 20 40 60 80 100

Leaching time, days

Figure 12. Concentration of various calcium ions in leachates collected during measurements from Texas 2 soil stabilizedwith 3%, 6%, and 9% portland cement and lime.


20

CONCLUSIONS

This investigation was performed to evaluate the per-formance of portland cement and hydrated lime in stabi-lization and in improving engineering properties ofseveral soils. Three soils with PI values ranging from 25 to42, obtained from California and Texas, were used. Inorder to make a one-to-one comparison between the per-formances of portland cement and hydrated lime as stabi-lizer, the dosages and testing methods were kept the same.Several characteristics, including engineering propertiesand long-term durability, were investigated. The follow-ing general conclusions can be drawn based upon theinvestigation performed.

1. Both portland cement and hydrated lime are effectivestabilizers for moderate to high plasticity clay soils.For the moderate PI soil (PI=25), portland cement per-forms better than lime even at dosages as low as 3%.For the high PI soils (PI 37 and 42), the performanceimproved significantly when the cement dosage wasincreased to 6% or more. At this dosage level, the per-formance of lime-stabilized soils, in general, was infe-rior to the cement-stabilized soil.

2. The maximum dry density of all three soils stabilizedwith portland cement attained higher maximum drydensity than the lime-stabilized soils. Optimum mois-ture content (OMC) for the three stabilized soilsincreased from 0% to 3% except for the lime stabilizedTexas 1 soil which increased 6%.

3. The unconfined compressive strength (UCS) of mod-erate PI soil stabilized with cement is almost alwayshigher than that of lime-stabilized soil. For high PI soil,lime stabilization produces a stronger product at 3%dosage level. However, at 6% and 9% dosages,cement-stabilized soils have generally higher UCS. Inorder to achieve high UCS, portland cement-stabilizedsoils should be compacted immediately after mixing.Delaying compaction by a day, which is practiced forlime stabilization, considerably reduces the UCS ofportland cement-stabilized soils.

4. Strength of cement-stabilized soil is generally higherthan lime-stabilized soil at all ages. Lime-stabilizedsoil starts weaker but gains strength with time. Theincrease in UCS of lime-stabilized soil is moredependent on time rather than dosage. The improve-ment in performance with higher dosage of cement isclearly noticeable. This suggests the dependence ofpozzolanic reaction for strength gain in the lime-sta-bilized soils.

5. California Bearing Ratios (CBR) measured for all threesoils stabilized with 6% and 9% cement or lime, clearlyindicate that cement-stabilized soils have superiorload bearing capacity. Even for the high PI soils,cement stabilization produced a stronger material.

6. The vacuum saturation test relates to the performancein freeze-thaw conditions. Over the soil PI range of 25to 42, soils stabilized with 6% and 9% cement had sig-nificantly higher strength than lime-stabilized soilsafter the vacuum saturation test, although significantloss of strength was encountered for both the stabiliz-ers, which is expected.

7. The physicochemical nature of cement-stabilized soils,particularly the moderate PI soil, results in better wet-dry durability. For high PI soils, cement-stabilizedsoils performed very similarly to those stabilized withlime at lower dosage level. However, at higher dosagelevel, the performance of cement-stabilized high PIsoils is, in general, superior.

8. Hydraulic conductivities of cement-stabilized moder-ate PI soils are significantly lower than lime-stabilizedones at all dosage levels. For high PI soils at a higherdosage (above 6%) level, permeability of cement-sta-bilized soils is generally lower than the lime-stabi-lized soils. At lower dosage levels (3% to 6%),hydraulic conductivity of cement-stabilized high PIsoils is about the same as lime-stabilized soils.

9. The concentration of calcium ions in leachates fromlime-stabilized soils is generally higher (as much as 2to 3 times at 9% dosage level) than those from cement-stabilized soils. Depending on the permeability, thecumulative loss of calcium from lime-stabilized soil ishigher, although the availability of calcium content ismore than that in soil stabilized with an equal dosageof cement.

10. An artificial increase of sulfate level of Cal soil appar-ently made the soil more plastic. This resulted in lossof UCS compared to the same stabilizer dosages usedfor the unsulfated Cal soil. Such spiking with sodiumsulfate solution may not produce a sulfated soil simi-lar to that found in the field. However, sulfate-relatedexpansion was measured for lime-stabilized sulfatedCal soil, and the corresponding cement-stabilized sul-fated soil did not register such an activity.

ACKNOWLEDGEMENTS

The research reported in this paper (PCA R&D SerialNo. 2435) was conducted by Construction TechnologyLaboratories, Inc., with the sponsorship of PortlandCement Association (PCA Project Index No. 94-15). Thecontents of this paper reflect the views of the authors, whoare responsible for the facts and accuracy of the data pre-sented. The contents do not necessarily reflect the views ofthe Portland Cement Association.


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REFERENCES

Bhattacharja, S., Bhatty, J.I., and Todres, H.A., Stabilization ofClay soils by Portland Cement or Lime – A Critical Review ofLiterature, Research and Development Serial No. 2066,Portland Cement Association, Skokie, Illinois, 2003.

Christensen, A.P., Cement Modification of Clay Soils, RD002,Portland Cement Association, Skokie, Illinois, 1969.

Stocker, P.T., “Diffusion and Diffuse Cementation in Limeand Cement-stabilized Clayey Soils – Chemical Aspects.”Australian Road Research, Vol. 5, No. 9, pp. 6-47, VermontSouth, Victoria, Australia, 1975.

Performance of Concrete Specimens in the PCA Outdoor Test Facility � RD124

RD125

This publication is intended SOLELY for use by PROFES-SIONAL PERSONNEL who are competent to evaluate thesignificance and limitations of the information providedherein, and who will accept total responsibility for theapplication of this information. The Portland CementAssociation DISCLAIMS any and all RESPONSIBILITYand LIABILITY for the accuracy of and the application ofthe information contained in this publication to the fullextent permitted by the law.

5420 Old Orchard RoadSkokie, Illinois 60077-1083 USA

847.966.6200Fax: 847.966.9781Internet: www.cement.org

An organization of cement companies to improveand extend the uses of portland cement and con-crete through market development, engineering, RD125

This publication is intended SOLELY for use by PROFES-SIONAL PERSONNEL who are competent to evaluate thesignificance and limitations of the information providedherein, and who will accept total responsibility for theapplication of this information. The Portland CementAssociation DISCLAIMS any and all RESPONSIBILITYand LIABILITY for the accuracy of and the application ofthe information contained in this publication to the fullextent permitted by the law.

5420 Old Orchard RoadSkokie, Illinois 60077-1083 USA

847.966.6200Fax: 847.966.9781Internet: www.cement.org

An organization of cement companies to improveand extend the uses of portland cement and con-crete through market development, engineering,research, education, and public affairs work.

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