ARMY TM 5-822-14AIR FORCE AFJMAN 32-1019

SOIL STABILIZATION FOR PAVEMENTS

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TM 5-822-14/AFJMAN 32-1019

REPRODUCTION AUTHORIZATION/RESTRICTIONS

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Copyrighted material included in the manual has been used with theknowledge and permission of the proprietors and is acknowledged assuch at point of use. Anyone wishing to make further use of anycopyrighted material, by itself and apart from this text, should seeknecessary permission directly from the proprietors.

Reprints or republications of this manual should include a creditsubstantially as follows: Joint Departments of the Army and AirForce, USA, TM 5-822-14/AFMAN 32-8010, Soil Stabilization forPavements, 25 October 1994.

If the reprint or republication includes copyrighted material, thecredit should also state: Anyone wishing to make further use ofcopyrighted material, by itself and apart from this text, should seeknecessary permission directly from the proprietors.

iATM 5-822-14/AFJMAN 32-1019

TECHNICAL MANUAL HEADQUARTERSNO. 5-822-14 DEPARTMENTS OF THE ARMY,AIR FORCE MANUAL AND THE AIR FORCENO. 32-1019 WASHINGTON, DC, 25 October 1994

SOIL STABILIZATION FOR PAVEMENTSParagraphPage

CHAPTER 1. INTRODUCTIONPurpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-1 1-1Scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-2 1-1References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-3 1-1Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-4 1-1Uses of Stabilization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-5 1-1

CHAPTER 2. SELECTION OF ADDITIVEFactors to be Considered. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1 2-1Use of Stabilized Soils in Forst Areas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-2 2-2Thickness Reduction for Base and Subbase Courses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-3 2-4

CHAPTER 3. DETERMINATION OF STABILIZER CONTENTStabilization with Portland Cement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1 3-1Stabilization with Lime. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2 3-3Stabilization with Lime-Fly Ash (LF) and Lime Centment-Fly Ash (LCF). . . . . . . . . . . . . . . . . . 3-3 3-5Stabilization with Bitumen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4 3-6Stabilization with Lime-Cement and Lime-Bitumen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-5 3-8Lime Treatemt of Expansive Soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-6 3-8

CHAPTER 4. DETERMINATION OF STABILIZER CONTENTConstruction with Portland Cement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1 4-1Construction with Lime. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2 4-10Construction with Lime-Fly Ash (LF) and Lime-Cement-Fly Ash (LCF). . . . . . . . . . . . . . . . . . . 4-3 4-20Construction with Bitumen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-4 4-20

CHAPTER 5. QUALITY CONTROLGeneral. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-1 5-1Cement Stabilization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-2 5-1Lime Stabilization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-3 5-1Lime-Fly Ash (LF) and Lime-Cement-Fly Ash (LCF). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-4 5-2Bituminous Stabilization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-5 5-2

APPENDIX A. REFERENCES A-1

APPENDIX B. pH TEST ON SOIL-CEMENT MIXTURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

APPENDIX C. DETERMINATION OF SULFATE IN SOILS, GRAVIMETRIC METHOD. . . . . . . . . . . . . . . C-1

APPENDIX D. pH TEST TO DETERMINE LIME REQUIREMENTS FOR LIME STABILIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-1

List of Figures

Figure 2-1. Gradation triangle for aid in selecting a commercial stabilizing agent. 2-23-1. Chart for the initial determination of lime content. 3-44-1. Transverse single-shaft mixer processing soil cement in place. Multiple passes are required.4-24-2. Multiple-transverse-shaft mixer mixing soil, cement, and water in one pass. 4-24-3. Windrow-type traveling pugmill mixing soil-cement from windrows of soil material. 4-24-4. Twin-shaft, continuous-flow central mixing plant mixing soil, cement, and water. 4-24-5. Batch-type central plant used for mixing soil-cement. 4-24-6. Rotary-drum central mixing plant. 4-24-7. Bulk portland cement being transferred pneumatically from a bulk transport truck to a job

truck. 4-34-8. Mechanical cement spreader attached to a job dump truck spreading cement in regulated

quantities. 4-34-9. Windrow-type mechanical spreader is used to place cement on the top of a slightly flattened

windrow of borrow soil material. 4-34-10. Sketch of soil-cement processing operations with windrow-type traveling pugmill. 4-54-11. Plan for processing with windrow-type traveling pugmill. 4-6

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TM 5-822-14/AFJMAN 32-1019

ii

List of Figures (cont*d)Page

Figure 4-12. Sketch of soil-cement processing operations with multiple-transverse-shaft traveling mixing machine. 4-6

4-13. Plan for processing with multiple-transverse-shaft traveling mixing machine. 4-74-14. Sketch of soil-cement processing operations with single-transverse shaft mixers. 4-84-15. In-place mixing of lime with existing base and paving material on city street. 4-114-16. Off-site mixing pads for Mississippi River levee repair project. 4-114-17. Deep stabilization after lime spreading the plow cuts 24 inches deep. 4-114-18. Root plow for scarifying to a depth of 18 inches. 4-114-19. Scarifying existing clay subgrade with lime on city street project. 4-114-20. Lime-treated gravel with lime fed by screw conveyor. 4-124-21. Lime-cement-fly ash aggregate base course. 4-124-22. Enclosed soil holds lime for adding to marginal crushed stone base material. 4-124-23. Lime slurry pressure injection (LSPI) rig treating a failed highway slope. 4-124-24. Application of lime by the bag for a small maintenance project. 4-134-25. Application of lime by a bulk pneumatic truck. 4-134-26. Bulk pneumatic truck spreading lime from bar spreader. 4-134-27. Distribution of quicklime from mechanical spreader on city street. 4-134-28. Spreading of granular quicklime. 4-154-29. Slurry mixing tank using recirculating pump for mixing hydrate and water. 4-164-30. Jet slurry mixing plant. 4-164-31. Spreading of lime slurry. 4-164-32. Recirculation pump on top of a 6,000-gallon wagon agitates slurry. 4-164-33. Grader-scarifier cutting slurry into stone base. 4-164-34. Portabatch lime slaker. 4-164-35. Watering of lime-treated clay on airport project. 4-184-36. Mixing with a disc harrow. 4-184-37. Rotary mixer. 4-184-38. Train of rotary mixers. 4-184-39. Rotary mixer on primary road project. 4-184-40. Self-propelled sheepsfoot roller. 4-194-41. Double sheepsfoot roller. 4-194-42. Pneumatic roller completes compaction of LCF base. 4-204-43. Vibrating roller completes compaction of subgrade. 4-204-44. Windrow-type pugmill travel plant. 4-214-45. Hopper-type pugmill travel plant. 4-214-46. Multiple rotary mixer. 4-214-47. A processing chamber of a multiple rotary mixer. 4-214-48. Single-shaft rotary mixer with asphalt supply tank. 4-224-49. Single-shaft rotary mixer without asphalt. 4-224-50. Mixing with motor grader. 4-224-51. Distributor applying asphalt. 4-224-52. Spreading and compacting train. 4-254-53. Stationary cold-mix plant. 4-264-54. Flow diagram of a typical cold-mix continuous plant. 4-264-55. Spreading cold mix with conventional paver. 4-264-56. Spreading cold mix with full-width cutter-trimmer modified for paving. 4-264-57. Jersey spreader. 4-274-58. Towed-type spreader. 4-27C-1. Example standard curve for spectrophotometer. C-3

List of Tables

Table 2-1. Guide for selecting a stabilizing additive. 2-32-2. Minimum unconfined compressive strength for cement, lime, lime-cement, and lime-cement-

fly ash stabilized soils. 2-42-3. Durability requirements. 2-43-1. Gradation requirements for cement stabilized base and subbase courses. 3-13-2. Cement requirements for various soils. 3-23-3. Gradation requirements for lime stabilized base and subbase courses. 3-33-4. Gradation requirements for fly ash stabilzed base and subbase courses. 3-53-5. Recommended gradations for bituminous stabilized subgrade materials. 3-73-6. Recommended gradations for bituminous stabilized base and subbase materials. 3-73-7. Emulsified asphalt requirements. 3-83-8. Swell potential of soils. 3-9

TM 5-822-14/AFJMAN 32-1019

CHAPTER 1

INTRODUCTION

1-1. Purpose. This manual establishes criteriafor improving the engineering properties of soilsused for pavement base courses, subbase courses,and subgrades by the use of additives which aremixed into the soil to effect the desired im-provement. These criteria are also applicable toroads and airfields having a stabilized surfacelayer.

1-2. Scope. This manual prescribes the appropri-ate type or types of additive to be used withdifferent soil types, procedures for determining adesign treatment level for each type of additive,and recommended construction practices for incor-porating the additive into the soil. It applies to allelements responsible for Army and Air Forcepavement and design construction.

1-3. References. Appendix A contains a list ofreferences used in this manual.

1-4. Definitions.a. Soils. Naturally occurring materials that are

used for the construction of all except the surfacelayers of pavements (i.e., concrete and asphalt) andthat are subject to classification tests (ASTM D2487) to provide a general concept of their engi-neering characteristics.

b. Additives. Manufactured commercial productsthat, when added to the soil in the proper quanti-ties, improve some engineering characteristics ofthe soil such as strength, texture, workability, andplasticity. Additives addressed in this manual arelimited to portland cement, lime, flyash, and bitu-men.

c. Stabilization. Stabilization is the process ofblending and mixing materials with a soil toimprove certain properties of the soil. The processmay include the blending of soils to achieve adesired gradation or the mixing of commerciallyavailable additives that may alter the gradation,texture or plasticity, or act as a binder for cemen-tation of the soil.

d. Mechanical stabilization. Mechanical stabili-zation is accomplished by mixing or blending soilsof two or more gradations to obtain a materialmeeting the required specification. The soil blend-ing may take place at the construction site, acentral plant, or a borrow area. The blendedmaterial is then spread and compacted to requireddensities by conventional means.

e. Additive stabilization. Additive stabilizationis achieved by the addition of proper percentagesof cement, lime, fly ash, bitumen, or combinationsof these materials to the soil. The selection of typeand determination of the percentage of additive tobe used is dependent upon the soil classificationand the degree of improvement in soil qualitydesired. Generally, smaller amounts of additivesare required when it is simply desired to modifysoil properties such as gradation, workability, andplasticity. When it is desired to improve thestrength and durability significantly, larger quan-tities of additive are used. After the additive hasbeen mixed with the soil, spreading and compac-tion are achieved by conventional means.

f. Modification. Modification refers to the stabi-lization process that results in improvement insome property of the soil but does not by designresult in a significant increase in soil strength anddurability.

1-5. Uses of Stabilization. Pavement design isbased on the premise that minimum specifiedstructural quality will be achieved for each layerof material in the pavement system. Each layermust resist shearing, avoid excessive deflectionsthat cause fatigue cracking within the layer or inoverlying layers, and prevent excessive permanentdeformation through densification. As the qualityof a soil layer is increased, the ability of that layerto distribute the load over a greater area isgenerally increased so that a reduction in therequired thickness of the soil and surface layersmay be permitted.

a. Quality improvement. The most common im-provements achieved through stabilization includebetter soil gradation, reduction of plasticity in-dex or swelling potential, and increases in durabil-ity and strength. In wet weather, stabilizationmay also be used to provide a working platformfor construction operations. These types of soilquality improvement are referred to as soil modifi-cation.

b. Thickness reduction. The strength and stiff-ness of a soil layer can be improved through theuse of additives to permit a reduction in designthickness of the stabilized material compared withan unstabilized or unbound material. Proceduresfor designing pavements that include stabilizedsoils are presented in TM 5-822-5/AFM 88-7,Chap. 3, TM 5-825-2/AFM 88-6, Chap. 2, TM

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TM 5-822-14/AFJMAN 32-1019

5-825-3/AFM 88-6, Chap. 3. The design thickness strength, stability, and durability requirementsof a base or subbase course can be reduced if the indicated in this Technical Manual for the particu-stabilized material meets the specified gradation, lar type of material.

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TM 5-822-14/AFJMAN 32-1019

CHAPTER 2

SELECTION OF ADDITIVE

2-1. Factors to be Considered. In the selectionof a stabilizer, the factors that must be consideredare the type of soil to be stabilized, the purpose forwhich the stabilized layer will be used, the type ofsoil improvement desired, the required strengthand durability of the stabilized layer, and the costand environmental conditions.

a. Soil types and additives. There may be morethan one candidate stabilizer applicable for onesoil type, however, there are some general guide-lines that make specific stabilizers more desirablebased on soil granularity, plasticity, or texture.Portland cement for example is used with a vari-ety of soil types; however, since it is imperativethat the cement be mixed intimately with thefines fraction (< .074 mm), the more plastic materi-als should be avoided. Generally, well-graded gran-ular materials that possess sufficient fines toproduce a floating aggregate matrix (homogenousmixture) and best suited for portland cement sta-bilization. Lime will react with soils of medium tohigh plasticity to produce decreased plasticity,increased workability, reduced swell, and in-creased strength. Lime is used to stabilize avariety of materials including weak subgrade soils,transforming them into a working table orsubbase; and with marginal granular base materi-als, i.e., clay-gravels, dirty gravels, to form astrong, high quality base course. Fly ash is apozzolanic material, i.e. it reacts with lime and istherefore almost always used in combination withlime in soils that have little or no plastic fines. Ithas often been found desirable to use a smallamount of portland cement with lime and fly ashfor added strength. This combination of lime-cement-flyash (LCF) has been used successfully inbase course stabilization. Asphalt or bituminousmaterials both are used for waterproofing and forstrength gain. Generally, soils suitable for asphaltstabilization are the silty sandy and granularmaterials since it is desired to thoroughly coat allthe soil particles.

b. Selection of candidate additives. The selectionof candidate/stabilizers is made using figure 2-1and table 2-1. The soil gradation triangle in figure2-1 is based upon the soil grain size characteris-tics and the triangle is divided into areas of soilswith similar grain size and therefore pulverizationcharacteristics. The selection process is continuedwith table 2-1 which indicates for each areashown in figure 2-1 candidate stabilizers and

restrictions based on grain size and/or plasticityindex (PI). Also provided in the second column oftable 2-1 is a listing of soil classification symbolsapplicable to the area determined from figure 2-1.This is an added check to insure that the properarea was selected. Thus, information on grain sizedistribution and Atterberg limits must be knownto initiate the selection process. Data required toenter figure 2-1 are: percent material passing theNo. 200 sieve and percent material passing theNo. 4 sieve but retained on the No. 200 (i.e., totalpercent material between the No. 4 and the No.200 sieves). The triangle is entered with these twovalues and the applicable area (1A, 2A, 3, etc.) isfound at their intersection. The area determinedfrom figure 2-1 is then found in the first columnof table 2-1 and the soil classification is checkedin the second column. Candidate stabilizers foreach area are indicated in third column andrestrictions for the use of each material are pre-sented in the following columns. These restrictionsare used to prevent use of stabilizing agents notapplicable for the particular soil type under consid-eration. For example, assume a soil classified as aSC, with 93 percent passing the No. 4 and 25percent passing the No. 200 with a liquid limit of20 and plastic limit of 11. Thus 68 percent of thematerial is between the No. 4 and No. 200 and theplasticity index is 9. Entering figure 2-1 with thevalues of 25 percent passing the No. 200 and 68percent between the No. 4 and No. 200, theintersection of these values is found in area 1-C.Then going to the first column of table 2-1, wefind area 1-C and verify the soil classification, SC,in the second column. From the third column allfour stabilizing materials are found to be potentialcandidates. The restrictions in the following col-umns are now examined. Bituminous stabilizationis acceptable since the PI does not exceed 10 andthe amount of material passing the No. 200 doesnot exceed 30 percent. However it should be notedthat the soil only barely qualifies under thesecriteria and bituminous stabilization probablywould not be the first choice. The restrictionsunder portland cement indicate that the PI mustbe less that the equation indicated in footnote b.Since the PI, 9, is less than that value, portlandcement would be a candidate material. The restric-tions under lime indicate that the PI not be lessthan 12 therefore lime is not a candidate materialfor stabilization, The restrictions under LCF stabi-

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TM 5-822-14/AFJMAN 32-1019

PERCENT BY WEIGHT, FINES(MATERAIL PASSING NO. 200 SIEVE)

Figure 2-1. Gradation triangle for aid in selecting a commercial stabilizing agent.

lization indicate that the PI must not exceed 25,thus LCF is also a candidate stabilizing material.At this point, the designer must make the finalselection based on other factors such as availabil-ity of material, economics, etc. Once the type ofstabilizing agent to be used is determined, samplesmust be prepared and tested in the laboratory todevelop a design mix meeting minimum engineer-ing criteria for field stabilization.

2-2. Use of stabilized soils in Frost Areas.a. Frost considerations. While bituminous, port-

land cement, lime, and LCF stabilization are themost common additives other stabilizers may beused for pavement construction in areas of frostdesign but only with approval obtained from theHQUSACE (CEMP-ET), Washington, DC 20314-1000 or the appropriate Air Force Major Com-mand.

2 - 2

b. Limitations. In frost areas, stabilized soil isonly used in one of the upper elements of apavement system if cost is justified by the reducedpavement thickness. Treatment with a lower de-gree of additive than that indicated for stabiliza-tion (i.e., soil modification) should be used in frostareas only with caution and after intensive tests,because weakly cemented material usually hasless capacity to endure repeated freezing andthawing than has firmly cemented material. Apossible exception is modification of a soil that willbe encapsulated within an impervious envelope aspart of a membrane-encapsulated-soil-layer pave-ment system. A soil that is unsuitable for encapsu-lation due to excessive moisture migration andthaw weakening may be made suitable for suchuse by moderate amounts of a stabilizing additive.Materials that are modified should also be testedto ascertain that the desired improvement is dura-

TM 5-822-14/AFJMAN 32-1019

Table 2-1. Guide for selecting a stabilizing additive.

ble through repeated freeze-thaw cycles. The im-provement should not be achieved at the expenseof making the soil more susceptible to ice segrega-tion.

c. Construction cutoff dates. Materials stabil-ized with cement, lime, or LCF should be con-structed early enough during the constructionseason to allow the development of adequatestrength before the first freezing cycle begins. Therate of strength gain is substantially lower at 50degrees Fahrenheit than at 70 or 80 degrees

Fahrenheit. Chemical reactions will not occurrapidly for lime-stabilized soils when the soiltemperature is less than 60 degrees Fahrenheitand is not expected to increase for one month, orcement-stabilized soils when the soil temperatureis less than 40 degrees Fahrenheit and is notexpected to increase for one month. In frost areas,it is not always sufficient to protect the mixturefrom freezing during a 7-day curing period asrequired by the applicable guide specifications,and a construction cutoff date well in advance of

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TM 5-822-14/AFJMAN 32-1019

the onset of freezing conditions (e.g. 30 days) may lime, LF, and LCF are indicated in tables 2-2be essential. and 2-3, respectively. For bituminous stabilized

2-3. Thickness Reduction for Base and SubbaseCourses. Stabilized base and subbase course mate-rials must meet certain requirements of grada-tion, strength, and durability to qualify for re-duced layer thickness design. Gradation require-ments are presented in the sections covering de-sign with each type of stabilizer. Unconfinedcompressive strength and durability requirementsfor bases and subbases treated with cement,

materials to qualify for reduced thickness, theymust meet strength requirements in TM 5-825-21AFM 88-6, Chap. 2. All stabilized materials ex-cept those treated with bitumen must meet mini-mum durability criteria to be used in pavementstructures. There are no durability criteria forbituminous stabilized materials since it is assumedthat they will be sufficiently waterproof if properlydesigned and constructed.

Table 2-2. Minimum unconfined compressive strength for cement, lime, lime-cement, and lime-cement-fly ash stabilized soils

Minimum Unconfined Compressive strength, psia

Stabilized Soil Layer Flexible pavement Rigid pavement

Base course 750 500Subbase course, select material or subgrade 250 200

a Unconfined compressive strength determined at 7 days for cement stabilization and 28 days for lime, lime fly ash, or lime-cement-flyash stabilization.

Table 2-3. Durability requirements

Type of Soil Stabilized

Granular, PI < 10Granular, PI > 210SiltClays

Maximum Allowable Weight Loss After 12 Wet-Dry orFreeze-Thaw Cycles Percent of Initial Specimen Weight

11886

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TM 5-822-14/AFJMAN 32-1019

CHAPTER 3

DETERMINATION OF STABILIZER CONTENT

3-1. Stabilization with Portland Cement. Port-land cement can be used either to modify andimprove the quality of the soil or to transform thesoil into a cemented mass with increased strengthand durability. The amount of cement used willdepend upon whether the soil is to be modified orstabilized.

a. Types of portland cement. Several differenttypes of cement have been used successfully forstabilization of soils. Type I normal portland ce-ment and Type IA air-entraining cements wereused extensively in the past and gave about thesame results. At the present time, Type II cementhas largely replaced Type I cement as greatersulfate resistance is obtained while the cost isoften the same. High early strength cement (TypeIII) has been found to give a higher strength insome soils. Type III cement has a finer particlesize and a different compound composition than dothe other cement types. Chemical and physicalproperty specifications for portland cement can befound in ASTM C 150.

b. Screening tests for organic matter and sul-fates. The presence of organic matter and/or sul-fates may have a deleterious effect on soil cement.Tests are available for detection of these materialsand should be conducted if their presence is sus-pected.

(1) Organic matter. A soil may be acid, neu-tral, or alkaline and still respond well to cementtreatment. Although certain types of organic mat-ter, such as undecomposed vegetation, may notinfluence stabilization adversely, organic com-pounds of lower molecular weight, such as nucleicacid and dextrose, act as hydration retarders andreduce strength. When such organics are presentthey inhibit the normal hardening process. A pHtest to determine the presence of organic material

is presented in appendix B. If the pH of a 10:1mixture (by weight) of soil and cement 15 minutesafter mixing is at least 12.0, it is probable thatany organics present will not interfere with nor-mal hardening.

(2) Sulfates. Although sulfate attack is knownto have an adverse effect on the quality of hard-ened portland cement concrete, less is knownabout the sulfate resistance of cement stabilizedsoils. The resistance to sulfate attack differs forcement-treated coarse-grained and fine-grainedsoils and is a function of sulfate concentrations.Sulfate-clay reactions can cause deterioration offine-grained soil-cement. On the other hand, gran-ular soil-cements do not appear susceptible tosulfate attack. In some cases the presence of smallamounts of sulfate in the soil at the time ofmixing with the cement may even be beneficial.The use of sulfate-resistant cement may not im-prove the resistance of clay-bearing soils, but maybe effective in granular soil-cements exposed toadjacent soils and/or ground water containing highsulfate concentrations. A procedure for determin-ing the percent SO4 is presented in appendix C.The use of cement for fine-grained soils containingmore than about 1 percent sulfate should beavoided.

c. Water for hydration. Potable water is nor-mally used for cement stabilization, although seawater has been found to be satisfactory.

d. Gradation requirements. Gradation require-ments for cement stabilized base and subbasecourses are indicated in table 3-1.

e. Cement content for modification of soils.(1) Improve plasticity. The amount of cement

required to improve the quality of the soil throughmodification is determined by the trial-and-errorapproach. If it is desired to reduce the PI of thesoil, successive samples of soil-cement mixtures

Table 3-1. Gradation requirements for cement stabilized base and subbase courses

Type Course Sieve Size Percent Passing

Base

Subbase

1 in. in.No. 4No. 40No. 200

1 in.No. 4No. 40No. 200

10070-10045-7010-400-20

10045-10010-500-20

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TM 5822-14 /FJMAN 32-1019

must be prepared at different treatment levels andthe PI of each mixture determined. The RefereeTest of ASTM D 423 and ASTM D 424 procedureswill be used to determine the PI of the soil-cementmixture. The minimum cement content that yieldsthe desired PI is selected, but since it was deter-mined based upon the minus 40 fraction of thematerial, this value must be adjusted to find thedesign cement content based upon total sampleweight expressed as

A = 100BC (eq 3-1)where

A = design cement content, percent totalweight of soil

B = percent passing No. 40 sieve size, ex-pressed as a decimal

C = percent cement required to obtain thedesired PI of minus 40 material, ex-pressed as a decimal

(2) Improve gradation. If the objective of modi-fication is to improve the gradation of a granularsoil through the addition of fines then particle-sizeanalysis (ASTM D 422) should be conducted onsamples at various treatment levels to determinethe minimum acceptable cement content.

(3) Reduce swell potential. Small amounts ofportland cements may reduce swell potential ofsome swelling soils. However, portland cementgenerally is not as effective as lime and may beconsidered too expensive for this application. Thedetermination of cement content to reduce theswell potential of fine-g-rained plastic soils can beaccomplished by molding several samples at vari-ous cement contents and soaking the specimensalong with untreated specimens for 4 days. Thelowest cement content that eliminates the swellpotential or reduces the swell characteristics to theminimum is the design cement content. Proceduresfor measuring swell characteristics of soils arefound in MIL-STD-621A, Method 101. The cementcontent determined to accomplish soil modificationshould be checked to see whether it provides anunconfined compressive strength great enough toqualify for a reduced thickness design in accord-ance with criteria established for soil stabilization.

(4) Frost areas. Cement-modified soil may alsobe used in frost areas, but in addition to theprocedures for mixture design described in (1) and(2) above, cured specimens should be subjected tothe 12 freeze-thaw cycles prescribed by ASTM D560 (but omitting wire-brushing) or other applica-ble freeze-thaw procedures. This should be followedby determination of frost design soil classificationby means of standard laboratory freezing tests. Ifcement-modified soil is used as subgrade, its frost-susceptibility, determined after freeze-thaw cy-

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cling, should be used as the basis of the pavementthickness design if the reduced subgrade designmethod is applied.

f. Cement content for stabilized soil. The follow-ing procedure is recommended for determining thedesign cement content for cement-stabilized soils.

(1) Step 1. Determine the classification andgradation of the untreated soil following proce-dures in ASTM D 422 and D 2487, respectively.

(2) Step 2. Using the soil classification selectan estimated cement content for moisture-densitytests from table 3-2.

Table 3-2. Cement requirements for various soils

Soil Classification

Initial EstimatedCement Content

percent dry weight

GW, SWGP, GW-GC, GW-GM, SW-SC, SW-SM

GC, GM, GP-GC, GP-GM, GM-GC, SC,SM, SP-SC, SP-SM, SM-SC, SP

CL. ML, MH 9

CH 11

(3) Step 3. Using the estimated cement con-tent, conduct moisture-density tests to determinethe maximum dry density and optimum watercontent of the soil-cement mixture. The procedurecontained in ASTM D 558 will be used to preparethe soil-cement mixture and to make the necessarycalculations; however, the procedures outlined inMIL-STD 621, Method 100 (CE 55 effort), orASTM D 1557 will be used to conduct the moisturedensity test.

(4) Step 4. Prepare triplicate samples of thesoil-cement mixture for unconfined compressionand durability tests at the cement content selectedin step 2 and at cement contents 2 percent aboveand 2 percent below that determined in step 2.The samples should be prepared at the density andwater content to be expected in field construction.For example, if the design density is 95 percent ofthe laboratory maximum density, the samplesshould also be prepared at 95 percent. The samplesshould be prepared in accordance with ASTM D1632 except that when more than 35 percent of thematerial is retained on the No. 4 sieve, a 4-inch-diameter by &inch-high mold should be used toprepare the specimens. Cure the specimens for 7days in a humid room before testing. Test threespecimens using the unconfined compression testin accordance with ASTM D 1633, and subjectthree specimens to durability tests, either wet-dry(ASTM D 559) or freeze-thaw (ASTM D 560) testsas appropriate. The frost susceptibility of the

TM 5-822-14/AFJMAN 32-1019

treated material should also be determined as indi-cated in appropriate pavement design manuals.

(5) Step 5. Compare the results of the uncon-fined compressive strength and durability testswith the requirements shown in tables 2-2 and2-3. The lowest cement content which meets therequired unconfined compressive strength require-ment and demonstrates the required durability isthe design cement content. If the mixture shouldmeet the durability requirements but not thestrength requirements, the mixture is consideredto be a modified soil. If the results of the speci-mens tested do not meet both the strength anddurability requirements, then a higher cementcontent may be selected and steps 1 through 4above repeated.

3-2. Stabilization with lime. In general, alllime treated finegrained soils exhibit decreasedplasticity, improved workability and reduced vol-ume change characteristics. However, not all soilsexhibit improved strength characteristics. Itshould be emphasized that the properties of soil-lime mixtures are dependent on many variables.Soil type, lime type, lime percentage and curingconditions (time, temperature, moisture) are themost important.

a. Types of lime. Various forms of lime havebeen successfully used as soil stabilizing agents formany years. However, the most commonly usedproducts are hydrated high-calcium lime, monohy-drated dolomitic lime, calcitic quicklime, and dolo-mitic quicklime. Hydrated lime is used most oftenbecause it is much less caustic than quicklime,however, the use of quicklime for soil stabilizationhas increased in recent years mainly with slurry-type applications. The design lime contents deter-mined from the criteria presented herein are forhydrated lime. If quicklime is used the design limecontents determined herein for hydrated limeshould be reduced by 25 percent. Specifications forquicklime and hydrated lime may be found inASTM C 977.

b. Gradation requirements. Gradation require-ments for lime stabilized base and subbase coursesare presented in table 3-3.

c. Lime content for lime-modified soils. Theamount of lime required to improve the quality ofa soil is determined through the same trial-and-error process used for cement-modified soils.

d. Lime content for lime-stabilized soils. Thefollowing procedures are recommended for deter-mining the lime content of lime stabilized soils.

(1) Step 1. The preferred method for determin-ing an initial design lime content is the pH test.In this method several lime-soil slurries are pre-

Table 3-3. Gradation requirements for lime stabilized baseand subbase courses

Type Course Sieve Size Percent Passing

Base

Subbase

1 in. in.No. 4No. 40No. 200

1 in.No. 4No. 40No. 200

10070-10045-7010-400-20

10045-10010-500-20

pared at different lime treatment levels such as 2,4, 6, and 8 percent lime and the pH of each slurryis determined. The lowest lime content at which apH of about 12.4 (the pH of free lime) is obtainedis the initial design lime content. Procedures forconducting the pH test are indicated in appendixD. An alternate method of determining an initialdesign lime content is by the use of figure 3-1.Specific values required to use figure 3-1 are thePI and the percent of material passing the No. 40sieve.

(2) Step 2. Using the initial design lime con-tent conduct moisture-density tests to determinethe maximum dry density and optimum watercontent of the soil lime mixture. The procedurescontained in ASTM D 3551 will be used to preparethe soil-lime mixture. The moisture density testwill be conducted following procedures inMIL-STD 621 Method 100 (CE 55 effort) or ASTMD 1557.

(3) Step 3. Prepare triplicate samples of thesoil lime mixture for unconfined compression anddurability tests at the initial design lime contentand at lime contents 2 and 4 percent above designif based on the preferred method or 2 percentabove at 2 percent below design if based on thealternate method. The mixture should he preparedas indicated in ASTM D 3551. If less than 35percent of the soil is retained on the No. 4 sieve,the sample should be approximately 2 inches indiameter and 4 inches high. If more than 35percent is retained on the No. 4 sieve, samplesshould be 4 inches in diameter and 8 incheshigh. The samples should be prepared at thedensity and water content expected in field con-struction. For example, if the design density is95 percent of the laboratory maximum density,the sample should be prepared at 95 percentdensity. Specimens should be cured in a sealedcontainer to prevent moisture loss and lime car-bonation. Sealed metal cans, plastic bags, and soforth are satisfactory. The preferred method ofcuring is 73 degrees F for 28 days. Accelerated

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TM 5-822-14/AFJMAN 32-1019

Figure 3-1. Chart for the initial determination of lime content.

curing at 120 degrees F for 48 hours has also beenfound to give satisfactory results; however, checktests at 73 degrees for 28 days should also beconducted. Research has indicated that if acceler-ated curing temperatures are too high, the pozzola-nic compounds formed during laboratory curingcould differ substantially from those that woulddevelop in the field.

(4) Step 4. Test three specimens using theunconfined compression test. If frost design is aconsideration, test three specimens to 12 cycles offreeze-thaw durability tests (ASTM D 560) exceptwire brushing is omitted. The frost susceptibilityof the treated material should be determined asindicated in appropriate design manuals.

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(5) Step 5. Compare the results of the uncon-fined compressive strength and durability testswith the requirements shown in tables 2-2 and2-3. The lowest lime content which meets theunconfined compressive strength requirement anddemonstrates the required durability is the designlime content. The treated material also must meetfrost susceptibility requirements as indicated inthe appropriate pavement design manuals. If themixture should meet the durability requirementsbut not the strength requirements, it is consideredto be a modified soil. If results of the specimenstested do not meet both the strength and durabil-ity requirements, a higher lime content may beselected and steps 1 through 5 repeated.

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3-3. Stabilization with Lime-Fly Ash (LF) andLime-Cement-Fly Ash (LCF). Stabilization ofcoarse-grained soils having little or no tines canoften be accomplished by the use of LF or LCFcombinations. Fly ash, also termed coal ash, is amineral residual from the combustion of pulver-ized coal. It contains silicon and aluminum com-pounds that, when mixed with lime and water,forms a hardened cementitious mass capable ofobtaining high compressive strengths. Lime andfly ash in combination can often be used success-fully in stabilizing granular materials since the flyash provides an agent, with which the lime canreact. Thus LF or LCF stabilization is often appro-priate for base and subbase course materials.

a. Types of fly ash. Fly ash is classified accord-ing to the type of coal from which the ash wasderived. Class C fly ash is derived from theburning of lignite or subbituminous coal and isoften referred to as high lime ash because itcontains a high percentage of lime. Class C fly ashis self-reactive or cementitious in the presence ofwater, in addition to being pozzolanic. Class F flyash is derived from the burning of anthracite orbituminous coal and is sometimes referred to aslow lime ash. It requires the addition of lime toform a pozzolanic reaction.

b. Evaluation of fly-ash. To be acceptable qualityfly ash used for stabilization must meet the re-quirements indicated in ASTM C 593.

c. Gradation requirements. Gradation require-ments for LF and LCF stabilized base and subbasecourse are indicated in table 3-4.

Table 3-4. Gradation requirements for fly ashstabilized base and subbase courses

Type Course

Base

Subbase

Sieve Size Percent Passing

2 in. 100 in. 70-1003/8 in. 50-80No. 4 35-70No. 8 25-55No. 16 10-45No. 200 0-15

1 in. 100No. 4 45-100No. 40 10-50No. 200 0-15

(1) Step 1. The first step is to determine theoptimum fines content that will give the maxi-mum density. This is done by conducting a seriesof moisture-density tests using different percent-ages of fly ash and determining the mix level thatyields maximum density. The initial fly ash con-tent should be about 10 percent based on dryweight of the mix. It is recommended that mate-rial larger than in. be removed and the testconducted on the minus in. fraction. Tests arerun at increasing increments of fly ash, e.g. 2percent, up to a total of about 20 percent. Moisturedensity tests should be conducted following proce-dures indicated in MIL-STD 621, Method 100 (CE55 effort) and ASTM D 1557. The design fly ashcontent is then selected at 2 percent above thatyielding maximum density. An alternate methodis to estimate optimum water content and conductsingle point compaction tests at fly ash contents of10-20 percent, make a plot of dry density versusfly ash content and determine the fly ash contentthat yields maximum density. The design fly ashcontent is 2 percent above this value. A moisturedensity test is then conducted to determine theoptimum water content and maximum dry density.

d. Selection of lime-fly ash content for LF and (2) Step 2. Determine the ratio of lime to flyLCF mixtures. Design with LF is somewhat differ- ash that will yield highest strength and durability.ent from stabilization with lime or cement. For a Using the design fly ash content and the optimumgiven combination of materials (aggregate, fly ash, water content determined in step 1, prepare tripli-and lime), a number of factors can be varied in the cate specimens at three different lime-fly ashmix design process such as percentage of lime-fly ratios following procedures indicated in MIL-STDash, the moisture content, and the ratio of lime to 621 Method 100 (less effort) or ASTM D 1557. Usefly ash. It is generally recognized that engineering LF ratios of 1:3, 1:4, and 1:5. If desired about 1

characteristics such as strength and durability aredirectly related to the quality of the matrix mate-rial. The matrix material is that part consisting offly ash, lime, and minus No. 4 aggregate fines.Basically, higher strength and improved durabilityare achievable when the matrix material is able tofloat the coarse aggregate particles. In effect,the fine size particles overfill the void spacesbetween the coarse aggregate particles. For eachcoarse aggregate material, there is a quantity ofmatrix required to effectively fill the availablevoid spaces and to float the coarse aggregateparticles. The quantity of matrix required formaximum dry density of the total mixture isreferred to as the optimum fines content. In LFmixtures it is recommended that the quantity ofmatrix be approximately 2 percent above theoptimum fines content. At the recommended finescontent, the strength development is also influ-enced by the ratio of lime to fly ash. Adjustment ofthe lime-fly ash ratio will yield different values ofstrength and durability properties.

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percent of portland cement may be added at thistime.

(3) Step 3. Test three specimens using theunconfined compression test. If frost design is aconsideration, subject three specimens to 12 cyclesof freeze-thaw durability tests (ASTM D 560) ex-cept wire brushing is omitted. The frost suscepti-bility of the treated material shall also be deter-mined as indicated in appropriate design manual.

(4) Compare the results of the unconfinedcompressive strength and durability tests with therequirements shown in tables 2-2 and 2-3. Thelowest LF ratio content, i.e., ratio with the lowestlime content which meets the required unconfinedcompressive strength requirement and demon-strates the required durability, is the design LFcontent. The treated material must also meet frostsusceptibility requirements as indicated in theappropriate pavement design manuals. If the mix-ture should meet the durability requirements butnot the strength requirements, it is considered tobe a modified soil. If the results of the specimenstested do not meet both the strength and durabil-ity requirements, a different LF content may beselected or additional portland cement used andsteps 2 through 4 repeated.

e. Selection of cement content for LCF mixtures.Portland cement may also be used in combinationwith LF for improved strength and durability. If itis desired to incorporate cement into the mixture,the same procedures indicated for LF designshould be followed except that, beginning at step2, the cement shall be included. Generally, about 1to 2 percent cement is used. Cement may be usedin place of or in addition to lime however, the totaltines content should be maintained. Strength anddurability tests must be conducted on samples atvarious LCF ratios to determine the combinationthat gives best results.

3-4. Stabilization with Bitumen. Stabilizationof soils and aggregates with asphalt differs greatlyfrom cement and lime stabilization. The basicmechanism involved in asphalt stabilization offine-grained soils is a waterproofing phenomenon.Soil particles or soil agglomerates are coated withasphalt that prevents or slows the penetration ofwater which could normally result in a decrease insoil strength. In addition, asphalt stabilization canimprove durability characteristics by making thesoil resistant to the detrimental effects of watersuch as volume. In noncohesive materials, such assands and gravel, crushed gravel, and crushedstone, two basic mechanisms are active: water-proofing and adhesion. The asphalt coating on thecohesionless materials provides a membrane which

prevents or hinders the penetration of water andthereby reduces the tendency of the material tolose strength in the presence of water. The secondmechanism has been identified as adhesion. Theaggregate particles adhere to the asphalt and theasphalt acts as a binder or cement. The cementingeffect thus increases shear strength by increasingcohesion. Criteria for design of bituminous stabi-lized soils and aggregates are based almost en-tirely on stability and gradation requirements.Freeze-thaw and wet-dry durability tests are notapplicable for asphalt stabilized mixtures.

a. Types of bituminous stabilized soils.(1) Sand bitumen. A mixture of sand and

bitumen in which the sand particles are cementedtogether to provide a material of increased stabil-ity.

(2) Gravel or crushed aggregate bitumen. Amixture of bitumen and a well-graded gravel orcrushed aggregate that, after compaction, providesa highly stable waterproof mass of subbase or basecourse quality.

(3) Bitumen lime. A mixture of soil, lime, andbitumen that, after compaction, may exhibit thecharacteristics of any of the bitumen-treated mate-rials indicated above. Lime is used with materialthat have a high PI, i.e. above 10.

b. Types of bitumen. Bituminous stabilization isgenerally accomplished using asphalt cement, cut-back asphalt, or asphalt emulsions. The type ofbitumen to be used depends upon the type of soilto be stabilized, method of construction, andweather conditions. In frost areas, the use of tar asa binder should be avoided because of its high-temperature susceptibility. Asphalts are affectedto a lesser extent by temperature changes, but agrade of asphalt suitable to the prevailing climateshould be selected. As a general rule, the mostsatisfactory results are obtained when the mostviscous liquid asphalt that can be readily mixedinto the soil is used. For higher quality mixes inwhich a central plant is used, viscosity-gradeasphalt cements should be used. Much bituminousstabilization is performed in place with the bitu-men being applied directly on the soil or soil-aggregate system and the mixing and compactionoperations being conducted immediately thereaf-ter. For this type of construction, liquid asphalts,i.e., cutbacks and emulsions, are used. Emulsionsare preferred over cutbacks because of energyconstraints and pollution control efforts. The spe-cific type and grade of bitumen will depend on thecharacteristics of the aggregate, the type of con-struction equipment, and climatic conditions. Gen-erally, the following types of bituminous materialswill be used for the soil gradation indicated:

3 - 6

(1) Open-graded aggregate.(a) Rapid- and medium-curing liquid as-

phalts RC-250, RC-800, and MC-3000.(b) Medium-setting asphalt emulsion MS-2

and CMS-2.(2) Well-graded aggregate with little or no

material passing the No. 200 sieve.(a) Rapid and medium-curing liquid as-

phalts RC-250, RC-800, MC-250, and MC-800.(b) Slow-curing liquid asphalts SC-250 and

SC-800.(c) Medium-setting and slow-setting asphalt

emulsions MS-2, CMS-2, SS-1, and CSS-1.(3) Aggregate with a considerable percentage

of fine aggregate and material passing the No. 200sieve.

TM 5-822-14/AFJMAN 32-1019

(a) Medium-curing liquid asphalt MC-250and MC-800.

(b) Slow-curing liquid asphalts SC-250 andSC-800.

(c) Slow-setting asphalt emulsions SS-1,SS-01h, CSS-1, and CSS-lh.The simplest type of bituminous stabilization isthe application of liquid asphalt to the surface ofan unbound aggregate road. For this type ofoperation, the slow- and medium-curing liquidasphalts SC-70, SC-250, MC-70, and MC-250 areused.

c. Soil gradation. The recommended soil grada-tions for subgrade materials and base or subbasecourse materials are shown in tables 3-5 and 3-6,respectively.

Table 3-5. Recommended gradations for bituminousstabilized subgrade materials

Sieve Size Percent Passing

3 in. 100No. 4 50-100No. 30 38-100No. 200 2-30

Table 3-6. Recommended gradations for bituminous-stabilized base and subbase materials

Sieve Size

1-in.l-in.-in.M-in.3/8-in.No. 4No. 8No. 16No. 30No. 50No. 100No. 200

1 in. 1-in. -in. -in.Maximum Maximum Maximum Maximum

100 - - -8 4 9 100 - -76 9 83 9 100 -66 9 73 9 82 9 10059 9 64 9 72 9 83 945 9 48 9 54 9 62 935 9 36 9 41 9 47 927 9 28 9 32 9 36 920 9 21 9 24 9 28 914 7 16 7 17 7 20 79 5 11 5 12 5 14 55 2 5 2 5 2 5 2

d. Mix design. Guidance for the design ofbituminous-stabilized base and subbase courses iscontained in TM 5-822-8/AFM 88-6, Chap. 9. Forsubgrade stabilization, the following equation maybe used for estimating the preliminary quantity ofcutback asphalt to be selected:

p = 0.02(a) + 0.07(b) + 0.15(c) + 0.20(d) X 100 (eq 3-2)(100 - S)

wherep = percent cutback asphalt by weight of dry

aggregatea = percent of mineral aggregate retained on

No. 50 sieveb = percent of mineral aggregate passing No.

50 sieve and retained on No. 100 sieve

c = percent of mineral aggregate passing No.100 and retained on No. 200 sieve

d = percent of mineral aggregate passing No.200

S = percent solventThe preliminary quantity of emulsified asphalt tobe used in stabilizing subgrades can be determinedfrom table 3-7. The final design content of cutbackor emulsified asphalt should be selected basedupon the results of the Marshal Stability testprocedure (MIL-STD 620A). The minimum Mar-shall Stability recommended for subgrades is 500pounds. If a soil does not show increased stabilitywhen reasonable amounts of bituminous materialsare added, the gradation of the soil should be

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Table 3-7. Emulsified asphalt requirements

Percent PassingNo. 200 Sieve

Pounds of Emulsified Asphalt per 100 pound of Dry Aggregate at Percent Passing No. 10 Sieve

TM 5-822-14/AFJMAN 32-1019

Table 3-8. Swell potential of soils

Liquid Limit Plasticity Index Potential Swell

>6050-603525-35

TM 5-822-14/AFJMAN 32-1019

CHAPTER 4

CONSTRUCTION PROCEDURES

4-1. Construction with Portland Cement.a. General construction steps. In soil-cement con-

struction the objective is to thoroughly mix apulverized soil material and cement in correctproportions with sufficient moisture to permitmaximum compaction. Construction methods aresimple and follow a definite procedure:

(1) Initial preparation(a) Shape the area to crown and grade.(b) If necessary, scarify, pulverize, and pre-

wet the soil.(c) Reshape to crown and grade.

(2) Processing(a) Spread portland cement and mix.(b) Apply water and mix.(c) Compact.(d) Finish.(e) Cure.

b. Mixing equipment. Soil, cement, and watercan be mixed in place using traveling mixingmachines or mixed in a central mixing plant. Thetypes of mixing equipment are

(1) Traveling mixing machines.(a) Flat-transverse-shaft type:

1 Single-shaft mixer (fig 4-1).2 Multiple-shaft mixer (fig 4-2).

(b) Windrow-type pugmill (fig 4-3).(2) Central mixing plants.

(a) Continuous-flow-type pugmill (fig 4-4).(b) Batch-type pugmill (fig 4-5).(c) Rotary-drum mixers (fig 4-6).

Whatever type of mixing equipment is used, thegeneral principles and objectives are the same.Some soil materials cannot be sufficiently pulver-ized and mixed in central mixing plants because oftheir high silt and clay content and plasticity.Almost all types of soil materials, from granular tofine grained, can be adequately pulverized andmixed with transverse-shaft mixers. The exceptionis material containing large amounts of highlyplastic clays. These clays may require more mix-ing effort to obtain pulverization. Revolving-bladecentral mixing plants and traveling pugmills canbe used for nonplastic to slightly plastic granularsoils. For coarse, nonplastic granular materials, arotary-drum mixer can provide a suitable mix;however, if the material includes a small amountof slightly plastic fines, mixing may not be ade-quate.

c. Equipment for handling and spreading ce-ment. There are a number of methods of handling

cement. On mixed-in-place construction using trav-eling mixing machines, bulk cement is spread onthe area to be processed in required amounts bymechanical bulk cement spreaders (fig 4-7). Bagcement is sometimes used on small jobs. Cementspreaders for mixed-in-place construction are oftwo general types: those that spread cement overthe soil material in a blanket (fig 4-8) and thosethat deposit cement on top of a partially flattenedor slightly trenched windrow of soil material (fig4-9). Cement meters on continuous-flow centralmixing plants are of three types: the belt withstrikeoff, screw, or vane. Cement for batch-type-pugmill mixers and rotary drum-mixers is batch-weighed.

d. Construction. Construction with soil cementinvolves two steps-preparation and processing.Variations in these steps, dictated by the type ofmixing equipment used, are discussed in thischapter. Regardless of the equipment and methodsused, it is essential to have an adequately com-pacted, thorough mixture of pulverized soil mate-rial and other proper amounts of cement andmoisture. The completed soil-cement must be ade-quately cured.

(1) Preparation. Before construction starts,crown and grade should be checked and any finegrading should be completed. Since there is littledisplacement of material during processing, gradeat the start of construction will determine finalgrade to a major extent. If borrow material is to beused, the subgrade should be compacted andshaped to proper crown and grade before theborrow is placed. Any soft subgrade areas shouldbe corrected. To avoid later costly delays, allequipment should be carefully checked to ensure itis in good operating condition and meets construc-tion requirements of the job. Guide stakes shouldbe set to control the width and guide the operatorsduring construction. Arrangements should bemade to receive, handle, and spread the cementand water efficiently. The number of cement andwater trucks required depends on length of haul,condition of haul roads, and anticipated rate ofproduction. For maximum production, an adequatecement and water supply is essential. The limits ofthe different materials and their correspondingcement requirements should be established by theproject engineer. Prewetting by adding moisturebefore cement is applied often saves time duringactual processing. Friable granular materials,

4-1

TM 5-822-14/AFJMAN 32-1019

Figure 4-1. Transverse single-shaft mixer processingsoil-cement in place. Multiple passes are required.

Figure 4-2. Multiple-transverseshaft mixer mixing soil,cement, and water in one pass.

Figure 4-3. Windrow-type traveling pugmill mixingsoil-cement from windrows of soil material.

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TM 5-822-14/AFJMAN 32-1019

Figure 4-7. Bulk portland cement being transferredpneumatically from a bulk transport truck to a job truck.

Figure 4-8. Mechanical cement spreader attached to ajob dump truck spreading cement in regulated quantities.

Figure 4-9. Windrow-type mechanical spreader placingcement on windrow.

which are most commonly used, require little or noscarification or pulverization. Silty and clayeysoils may require extra effort to pulverize them,particularly if they are too dry or too wet. Soilsthat are difficult to pulverize when dry and brittlecan be broken down readily if water is added andallowed to soak in; whereas, sticky soils can bepulverized more easily when they have been driedout a little. Most specifications require that thesoil material be pulverized sufficiently so that atthe time of compaction 100 percent of the soil-cement mixture will pass a l-inch sieve and aminimum of 80 percent will pass a No. 4 sieve,exclusive of any gravel or stone. Gravel or stoneshould be no more than 2-inches maximum size.The final pulverization test should be made at theconclusion of mixing operations. When borrowmaterial is specified, it should be distributed on anaccurately graded, well-compacted roadway in aneven layer or uniform windrow, depending on thetype of mixing equipment to be used. It should beplaced by weight or volume as required by thespecifications.

(2) Processing. For maximum efficiency and tomeet specification time limits, a days work shouldbe broken down into several adjacent sectionsrather than one or two long sections. This proce-dure will result in maximum daily production andwill prevent a long stretch of construction frombeing rained out in case of a sudden severerainstorm.

(a) Handling and spreading cement. Bulkcement is normally trucked to the jobsite in bulktransport trucks or shipped to the nearest railroadsiding in enclosed hopper cars. Compressed air orvibrators are used to loosen the cement in thehopper cars during unloading. Transfer to cementtrucks is done pneumatically or by a screen or beltconveyor. The trucks are usually enclosed or fittedwith canvas covers. The cement is weighed intruckloads on portable platform scales or at anearby scale. Soil materials that contain excessiveamounts of moisture will not mix readily withcement. Sandy soils can be mixed with a moisturecontent at optimum or slightly above; whereas,clayey soils should have a moisture content belowoptimum when cement is spread. Cement shouldnot be applied onto puddles of water. If the soilmaterial is excessively wet, it should be aerated todry it before cement is applied. Handling andspreading procedures for different types of equip-ment are presented below.

1. Mechanical cement spread, mixed-in-place construction. A mechanical cement spreaderis attached to the dump truck. As the truck movesforward, cement flows through the spreader, which

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TM 5-822-14/AFJMAN 32-1019

regulates the quantity of cement placed on theprepared soil. To obtain a uniform cement spread,the spreader should be operated at a constant,slow speed and with a constant level of cement inthe hopper. A true line at the pavement edgeshould be maintained with a string line. Themechanical spreader must have adequate tractionto produce a uniform cement spread. Traction canbe aided by wetting and rolling the soil materialbefore spreading the cement. When operating inloose sands or gravel, slippage can be overcome bythe use of cleats on the spreader wheels or byother modifications; sometimes, the spreader ismounted on a tractor or high lift. The mechanicalcement spreader can also be attached directlybehind a bulk cement truck. Cement is thenmoved pneumatically from the truck through anair separator cyclone that dissipates the air pres-sure, and falls into the hopper of the spreader.Forward speed must be slow and even. Sometimesa motor grader or loader pulls the truck to main-tain this slow, even forward speed. Pipe cementspreaders attached to cement transport truckshave been used in some areas with variableresults. Improvements in this type of equipmentare being made.

2. Bagged-cement spread, mixed-in-placeconstruction. When bags of cement are used onsmall jobs, a simple but exact method for properlyplacing the bags is necessary. The bags should bespaced at approximately equal transverse andlongitudinal intervals that will ensure the properpercentage of cement. Positions can be spotted byflags or markers fastened to chains at proper inter-vals to mark the transverse and longitudinal rows.When the bags are opened, the cement should bedumped so that it forms fairly uniform transversewindrows across the area being processed. A spike-tooth harrow, a nail drag, or a length of chain-linkfence can be used to spread the cement evenly.The drag should make at least two round tripsover the area to spread the cement uniformly.

3. Cement application, central-mixing-plant construction. When a continuous-flow centralmixing plant is used, the cement is usually me-tered onto the soil aggregate and the two materi-als are carried to the pugmill mixer on the mainfeeder belt. Variations in moisture and in grada-tion of the soil aggregate will result in variationsin the amount of material being fed onto thefeeder belt. A high bulkhead placed in front of thesoil hopper will help to obtain a more uniform flowthrough the soil material feeder. The chance ofloss of cement due to wind can be minimized bythe use of a small plow attachment that will forma furrow for the cement in the soil aggregate.

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After the cement is added, a second plow attach-ment a little farther up on the main feeder beltcloses the furrow and covers the cement. A coveron the main feeder belt will also minimize cementloss due to wind. One of three types of cementmeters-belt, screw, or vane-can be used to pro-portion the cement on a volumetric basis. Eachrequires a 450- to 750-pound capacity surge tankor hopper between the cement silo and the cementfeeder. This tank maintains a constant head ofcement for the feeder, thus providing a moreuniform cement discharge. Compressed air of 2- to4-pounds per square inch pressure should be usedto prevent arching of cement in the silo and thesurge tank. Portable vibrators attached to thesurge tank can be used instead of air jets. Apositive system should be included to stop theplant automatically if the cement flow suddenlystops. The correct proportion of cement, soil mate-rial, and water entering the mixing chamber mustbe determined by calibrating the plant beforemixing and placing operations begin.

(b) Mixing and application of water. Proce-dures for applying water and mixing depend onthe type of mixing machine used. A thoroughmixture of pulverized soil material, cement, andwater must be obtained. Uniformity of the mix iseasily checked by digging trenches or a series ofholes at regular intervals for the full depth oftreatment and inspecting the color of the exposedsoil-cement mixture. Uniform color and texturefrom top to bottom indicate a satisfactory mix; astreaked appearance indicates insufficient mixing.Proper width and depth of mixing are also impor-tant. Following are methods of applying water andmixing for the different types of mixing machines.

1. Windrow-type traveling mixing ma-chine. Windrow-type traveling mixing machineswill pulverize friable soil materials. Other soils,however, may need preliminary pulverizing tomeet specification requirements. This is usuallydone before the soil is placed in windrows forprocessing. The prepared soil material is bladedinto windrows and a proportion pulled along tomake them uniform in cross section. When borrowmaterials are used, a windrow spreader can beused to proportion the material. Nonuniform wind-rows cause variations in cement content, moisturecontent, and pavement thickness. The number andsize of windrows needed depend on the width anddepth of treatment and on the capacity of themixing machine. Cement is spread on top of thepartially flattened or slightly trenched, preparedwindrow. The mixing machine then picks up thesoil material and cement and dry-mixes them withthe first few paddles in the mixing drum. At that

point water is added through spray nozzles and theremaining paddles complete the mixing. A strike-off attached to the mixing machine spreads themixed soil-cement. If a motor grader is used tospread the mixture and a tamping roller is usedfor compaction, the mixture should first be loos-ened to ready it for compaction. If two windrowshave been made, the mixing machine progresses350 to 500 feet along one windrow and then isbacked up to process the other windrow for 700 to1,000 feet. The cement spreading operation is keptjust ahead of the mixing operation. Water issupplied by tank trucks. A water tank installed onthe mixer will permit continuous operation while

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the tank trucks are being switched. As soon as thefirst windrow is mixed and spread on one sectionof the roadway, it is compacted. At the same timea second windrow is being mixed and spread. It inturn is then compacted. Finishing of the entireroadway is completed in one operation. Waterrequirements are based on the quantity of soilmaterial and cement per unit length of windrow.See figures 4-10 and 4-11 for construction se-quences for windrow-type operations.

2. Multishaft traveling mixing machine.Since most multi-shaft traveling mixing machineshave a high-speed pulverizing rotor, preliminarypulverization is usually unnecessary. The onlypreparation required is shaping the soil material

Figure 4-10. Sketch of soil-cement processing operations with windrow-type traveling pugmill.

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2 WINDROWS

3 WINDROWS

Figure 4-11. Plan for processing with windrow-typetraveling pugmill.

to approximate crown and grade. If an old roadbedis extremely hard and dense, prewetting and scari-fication will facilitate processing. Processing isdone in lanes 350 to 500 feet long and as wide asthe mixing machine. Cement is spread on the soilmaterial in front of the mixing machine. Cement

spreading should be completed in the first workinglane and under way in the second lane beforemixing operations are begun. This ensures a full-width cement spread without a gap between lanesand keeps spreading equipment out of the way ofmixing equipment. See figures 4-12 and 4-13 foran illustration of the construction sequence.

3. Single-shaft traveling mixing machine.Soil-cement construction with single-shaft travel-ing mixers differs from the preceding examples inthat more than one mixing pass is required. Thebasic principles and objectives are the same, how-ever. Shaping, scarifying, and pulverizing theroadway are the first steps of preparation, asdescribed previously in this chapter. Since mostsingle-shaft traveling mixers were not designed toscarify, the soil material may need to be loosenedwith a scarifier. Prewetting the soil material iscommon practice. Applying water at this stage of

Figure 4-12. Sketch of soil-cement processing operations with multiple-transverse-shaft traveling mixing machine.

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2 LANES 3 LANES

Figure 4-13. Plan for processing withmultiple-transverse-shaft traveling mixing machine.

construction saves time during actual processingoperations because most of the required water willalready have been added to the soil material. Invery granular materials, prewetting prevents ce-ment from sifting to the bottom of the mix bycausing it to adhere more readily to the sand andgravel particles. Mixing the soil material andcement is easier if the moisture content of the rawmaterial is two or three percentage points belowoptimum. However, very sandy materials can bemixed even if the moisture content is one or twopercentage points above optimum. Moisture shouldbe applied uniformly during prewetting. By mix-ing it into the soil material, evaporation losses arereduced. Because of the hazard of night rains,some prefer to do the prewetting in the earlymorning. After scarifying and prewetting, theloose, moist soil material is shaped to crown andgrade. Cement is spread by a mechanical cementspreader or from bags. Occasionally, the prewetsoil material becomes compacted by cement-spreading equipment. In such cases, mixing can behastened by loosening the material again aftercement is spread, usually with the scarifier on amotor grader. The scarifier teeth should be set sothat the cement will flow between them and not becarried forward or displaced by the scarifier frame.The mixer picks up the soil material and cement

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and mixes them in place. Water, supplied by atank truck, is usually applied to the mixture by aspray bar mounted in the mixing chamber, or itcan be applied ahead of the mixer by waterpressure distributors. The soil material and ce-ment must be sufficiently blended when watercontacts the mixture to prevent the formation ofcement balls. The number of mixing passes de-pends on the type of soil material and its moisturecontent and on the forward speed of the mixer. Seefigure 4-14 for construction sequences.

(c) Central mixing plant. Central mixingplants are often used for projects involving borrowmaterials. The basic principles of thorough mixing,adequate cement content, proper moisture content,and adequate compaction apply. Friable granularborrow materials are generally used because oftheir low cement requirements and ease in han-dling and mixing. Pugmill-type mixers, eithercontinuous flow or batch, or rotary-drum mixersare used for this work. Generally the twin-shaftcontinuous-flow pugmill is used on highwayprojects. Facilities for efficiently storing, handling,and proportioning materials must be provided atthe plant. Quantities of soil material, cement, andwater can be proportioned by volume for weight.Mixing is continued until a uniform mixture ofsoil material, cement, and water is obtained. Toreduce evaporation losses during hot, windy condi-tions and to protect against sudden showers, haultrucks should be equipped with protective covers.To prevent excessive haul time, not more than 60minutes should elapse between the start of moist-mixing and the start of compaction. Haul time isusually limited to 30 minutes. The mixed soil-cement should be placed on the subgrade withoutsegregation in a quantity that will produce acompacted base of uniform density conforming tothe specified grade and cross section. The mixtureshould be spread to full roadway width either byone full-width spreader or by two or more spread-ers operating in staggered positions across theroadway. Less preferable is the use of one piece ofspreading equipment operating one lane at a timein two or more lanes. No lane should be spread sofar ahead of the adjoining lane that a time lapse ofmore than 30 minutes occurs between the time ofplacing material in adjoining lanes at any loca-tion. The subgrade should be damp when thesoil-cement is placed. Bituminous pavers havebeen used for spreading soil-cement although mod-ification may be necessary to increase volumecapacity before they can be used. Compactionequipment should follow immediately behind thespreader. When compacting the first lane, a nar-row compacted ridge should be left adjacent to the

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Figure 4-14. Sketch of soil-placement processing operations with single-transverse-shaft mixers.

second lane to serve as a depth guide when placingthe mix in the second lane. Water spray equip-ment should be available to keep the joint areasdamp. The amount of water needed to bring thesoil-cement mixture to required moisture contentin continuous-flow-type mixing plants is based onthe amount of soil material and cement cominginto the mixing chamber per unit of time. Theamount of water required in batch-type centralmixing plants is similarly calculated, using theweights of soil material and cement for each batch.

(3) Compaction. The principles governing com-paction of soil-cement are the same as those forcompacting the same soil materials without ce-ment treatment. The soil-cement mixture at opti-mum moisture should be compacted to maximumdensity and finished immediately. Moisture loss byevaporation during compaction, indicated by agreying of the surface, should be replaced withlight applications of water. Tamping rollers are

generally used for initial compaction except for themore granular soils. Self-propelled and vibratorymodels are also used. To obtain adequate compac-tion, it is sometimes necessary to operate therollers with ballast to give greater unit pressure.The general rule is to use the greatest contactpressure that will not exceed the bearing capacityof the soil-cement mixture and that will stillwalk out in a reasonable number of passes.Friable silty and clayey sandy soils will compactsatisfactorily using rollers with unit pressures of75 to 125 pounds per square inch. Clayey sands,lean clays, and silts that have low plasticity canbe compacted with 100- to 200-pounds per squareinch rollers. Medium to heavy clays and gravellysoils required greater unit pressure, i.e., 150 to300 pounds per square inch. Compacted thicknessup to 8 or 9 inches can be compacted in one lift.Greater thicknesses can be compacted with equip-ment designed for deeper lifts. When tamping

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rollers are used for initial compaction, the mixedmaterial must be in a loose condition at the startof compaction so that the feet will pack the bottommaterial and gradually walk out on each succeed-ing pass. If penetration is not being obtained, thescarifier on a motor grader or a traveling mixercan be used to loosen the mix during start ofcompaction, thus allowing the feet to penetrate.Vibratory-steel-wheeled rollers and grid and seg-mented rollers can be used to satisfactorily com-pact soil-cement made of granular soil materials.Vibratory-plate compactors are used on nonplasticgranular materials. Pneumatic-tired rollers can beused to compact coarse sand and gravel soil-cement mixtures with very little plasticity andvery sandy mixtures with little or no bindermaterial, such as dune, beach, or blow sand. Somepermit rapid inflation and deflation of the tireswhile compacting to increase their versatility.Pneumatic-tired rollers pulled by track-type trac-tors equipped with street plates can be used tocompact cohesionless sand mixtures. The weightand vibration of the tractor aid in compaction.Heavy three-wheeled steel rollers can be used tocompact coarse granular materials containing lit-tle or no binder material. Gravelly soils thatcontain up to about 20 percent passing the No. 200sieve and have low plasticity are best suited forcompaction with these rollers. Tandem-steel-wheeled rollers are often used during final rollingto press down or set rock particles and to smoothout ridges. There are two general types of roadcross section: trench and featheredge. Both can bebuilt satisfactorily with soil-cement. In trench-typeconstruction, the shoulder material gives lateralsupport to the soil-cement mixture during compac-tion. In the featheredge type of construction, theedges are compacted first to provide some edgestability while the remaining portion is beingcompacted. The edge slope should not be steeperthan 2:1 to facilitate shaping and compacting.Shoulder material is placed after the soil-cementhas been finished. Occasionally, during compactionand finishing, a localized area may yield under thecompaction equipment. This may be due to one ormore causes: the soil-cement mix is much wetterthan optimum moisture; the subsoil may be wetand unstable; or the roller may be too heavy forthe soil. If the soil-cement mix is too damp, itshould be aerated with a cultivator, travelingmixer, or motor grader. After it has dried to nearoptimum moisture, it can be compacted. For bestresults, compaction should start immediately afterthe soil material, cement, and water have beenmixed. Required densities are then obtained more

readily; there is less water evaporation; and dailyproduction is increased.

(4) Finishing. There are several acceptablemethods for finishing soil-cement. The exact proce-dure depends on equipment, job conditions, andsoil characteristics. Regardless of method, the fun-damental requirements of adequate compaction,close to optimum moisture, and removal of allsurface compaction planes must be met to producea high quality surface. The surface should besmooth, dense, and free of ruts, ridges, or cracks.When shaping is done during finishing, all smoothsurfaces, such as tire imprints and blade marks,should be lightly scratched with a weeder, naildrag, coil spring, or spiketooth harrow to removecleavage or compaction planes from the surface.Scratching should be done on all soil-cement mix-tures except those containing appreciable quanti-ties of gravel. The surface should be kept dampduring finishing operations. Steel-wheeled rollerscan be used to smooth out ridges left by the initialpneumatic-tired rolling. Steel-wheeled rollers areparticularly advantageous when rock is present inthe surface. A broom drag can sometimes be usedadvantageously to pull binder material in andaround pieces of gravel that have been set by thesteel-wheeled roller. Instead of using a steel roller,surfaces can be shaved with the motor grader andthen rerolled with a pneumatic-tired roller to sealthe surface. Shaving consists of lightly cutting offany small ridges left by the finishing equipment.Only a very thin depth is cut and all materialremoved is bladed to the edge of the road andwasted. The final operation usually consists of alight application of water and rolling with apneumatic-tired roller to seal the surface. Thefinished soil-cement is then cured.

(5) Curing. Compacted and finished soil-cement contains sufficient moisture for adequatecement hydration. A moisture-retaining cover isplaced over the soil-cement soon after completionto retain this moisture and permit the cement tohydrate. Most soil-cement is cured with bitumi-nous material, but other materials such as water-proof paper of plastic sheets, wet straw or sand,fog-type water spray, and wet burlap or cottonmats are entirely satisfactory. The types of bitumi-nous materials most commonly used are RC-250,MC-250, RT-5, and emulsified asphalt SS-1. Rateof application varies from 0.15 to 0.30 US gallonsper square yard. At the time of application, thesoil-cement surface should be free of all dry, looseand extraneous material. The surface should alsobe moist when the bituminous materials are ap-plied. In most cases a light application of water is

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placed immediately ahead of the bituminous appli-cation.

(6) Construction joints. After each days con-struction, a transverse vertical construction jointmust be formed by cutting back into the completedsoil-cement to the proper crown and grade. This isusually done the last thing at night or the firstthing the following morning, using the toe of themotor-grader blade or mixer. The joint must bevertical and perpendicular to the centerline. Afterthe next days mixing has been completed at thejoint, it must be cleaned of all dry and unmixedmaterial and retrimmed if necessary. Mixed moistmaterial is then bladed into the area and com-pacted thoroughly. The joint is left slightly highuntil final rolling when it is trimmed to gradewith the motor grader and rerolled. Joint construc-tion requires special attention to make sure thejoints are vertical and the material in the jointarea is adequately mixed and thoroughly com-pacted. When bituminous material is used as acuring agent, it should be applied right up to thejoint and sanded to prevent pickup.

(7) Multiple-layer construction. When the spec-ified thickness of soil-cement base course exceedsthe depth (usually 8 or 9 inches compacted) thatcan be compacted in one layer, it must be con-structed in multiple layers. No layer should be lessthan 4 inches thick. The lower layer does not haveto be finished to exact crown and grade, nor dosurface compaction planes have to be removedsince they are too far from the final surface to beharmful. The lower layer can be cured with themoist soil that will subsequently be used to buildthe top layer-which can be built immediately, thefollowing day, or some time later. With mixed-in-place construction, care must be taken to elimi-nate any raw-soil seams between the layers.

e. Special construction problems.(1) Rainfall. Attention to a few simple precau-

tions before processing will greatly reduce thepossibility of serious damage from wet weather.For example, any loose or pulverized soil should becrowned so it will shed water, and low places inthe grade where water can accumulate should betrenched so the water will drain off freely. Asshown by the construction of millions of squareyards of soil-cement in all climates, it is unlikelythat rainfall during actual construction will be aserious problem to the experienced engineer orcontractor. Usually construction requires the addi-tion of water equivalent to 1 to 1 inches of rain.If rain falls during cement-spreading operations,spreading should be stopped and the cement al-ready spread should be quickly mixed into the soilmass. A heavy rainfall that occurs after most of

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the water has already been added, however, can beserious. Generally, the best procedure is to obtainrapid compaction by using every available piece ofequipment so that the section will be compactedand shaped before too much damage results. Insuch instances it may be necessary to completefinal blading later; any material bladed from thesurface is wasted. After the mixture has beencompacted and finished, rain will not harm it.

(2) Wet soils. Excessively wet material is diffi-cult to mix and pulverize. Experience has shownthat cement can be mixed with sandy materialswhen the moisture content is as high as 2 percentabove optimum. For clayey soils, the moisturecontent should be below optimum for efficientmixing. It may be necessary to dry out the soilmaterial by aeration. This can be done by usingsingle-shaft traveling mixers with the hood in araised position, or by cutting out the material withthe tip of a motor grader blade and working andaerating with a disc. The maintenance of goodcrown and surface grade to permit rapid runoff ofsurface water before soil-cement processing is thebest insurance against excessive amounts of wetmaterial.

(3) Cold weather. Soil-cement, like othercement-using products, hardens as the cementhydrates. Since cement hydration practicallyceases when temperatures are near or below freez-ing, soil-cement should not be placed when thetemperature is 40 degrees F or below. Moreover, itshould be protected to prevent its freezing for aperiod of 7 days after placement, and until it hashardened, by a suitable covering of hay, straw, orother protective material.

4-2. Construction with lime.a. Lime stabilization methods. Basically, there

are three recognized lime stabilization methods;in-place mixing, plant mixing, and pressure injec-tion.

(1) In-place mixing.(a) In-place mixing may be subdivided into

three methods: mixing lime with the existingmaterials already a part of the construction site orpavement (fig 4-15); off-site mixing in which limeis mixed with borrow and the mixture is thentransported to the construction site for final ma-nipulation and compaction (fig 4-16); and mixingin which the borrow source soil is hauled to theconstruction site and processed as in the firstmethod.

(b) The following procedures are for in-placemixing:

One increment of lime is added to clays orgranular base materials that are easy to pulverize.

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Figure 4-15. In-place mixing of lime with existing baseand paving material on city street.

Figure 4-16. Off-site mixing pads for Mississippi Riverlevee repair project.

The material is mixed and compacted in oneoperation, and no mellowing period is required.

One increment of lime is added and themixture is allowed to mellow for a period of 1 to 7days to assist in breaking down heavy clay soils.(The term mellow refers to the reaction of the limeon clay to make it more friable and easier topulverize.)

One increment of lime is added for soil modifi-cation and pulverization before treatment withcement or asphalt.

One increment of lime is added to produce aworking table. Proof rolling is required instead ofpulverization and density requirements.

Two increments of lime are added for soilsthat are extremely difficult to pulverize. Betweenthe applications of the first and second incrementsof lime, the mixture is allowed to mellow.

(c) Deep stabilization may be accomplishedby one of two approaches.

One increment of lime is applied to modify soilto a depth of 24 inches (fig 4-17 through fig 4-19).Greater depths are possible but to date have notbeen attempted. A second increment of lime is

Figure 4-17. Deep stabilization after lime spreadingthe plow cuts 24 inches deep.

Figure 4-18. Root plow for scarifying to a depth of 18 inches.

Figure 4-19. Scarifying existing clay subgrade with lime oncity street project.

added to the top 6 to 12 inches for completestabilization. Plows and rippers are used to breakdown the large clay chunks in the deep treatment.Heavy disc harrows and blades are also used inpulverization of these clay soils. In frost zones, the

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use of small quantities of lime for soil modificationunder some circumstances may result in a frostsusceptible material that in turn can produce aweak sublayer.

One increment of lime is applied for completestabilization to a depth of 18 inches. Mechanicalmixers are now available to pulverize the lime-clay soil to the full depth by progressive cuts asfollows: first-pass cut to a depth of 6 inches, secondto 9 inches, third to 12 inches, fourth to 15 inches,and then a few passes to a depth of 18 inches toaccomplish full pulverization. The full 18 inches iscompacted from the top by vibratory and conven-tional heavy rollers.

(2) Plant mixing. The plant-mix operation usu-ally involves hauling the soil to a central plantwhere lime, soil, and water are uniformly mixedand then transported to the construction site forfurther manipulation (fig 4-20 through fig 4-22).The amount of lime for either method is usuallypredetermined by test procedures. Specificationsmay be written to specify the actual strength gainrequired to upgrade the stabilized soil, and nota-tions can be made on the plans concerning theestimated percent of lime required. This noteshould also stipulate that changes in lime c