soilo

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CHAPTER 9

S o i l S t a b i l i z a t i o n

f o r R o a d s a n d A i r f i e l d s

Soil stabilization is the alteration of one ormore soil properties, by mechanical or chemi-

cal means, to create an improved soil materialpossessing the desired engineering proper-ties. Soils may be stabilized to increasestrength and durability or to prevent erosionand dust generation. Regardless of the pur-pose for stabilization, the desired result is thecreation of a soil material or soil system thatwill remain in place under the design use con-ditions for the design life of the project.

Engineers are responsible for selecting orspecifying the correct stabilizing method,technique, and quantity of material required.

his chapter is aimed at helping to ma!e thecorrect decisions. "any of the proceduresoutlined are not precise, but they will #get youin the ball par!.$ Soils vary throughout theworld, and the engineering properties of soilsare equally variable. he !ey to success insoil stabilization is soil testing. he methodof soil stabilization selected should be verifiedin the laboratory before construction and

preferably before specifying or orderingmaterials.

Section ! Met"ods ofStabilization

#ASC C$%S&ERAT$%S

%eciding to stabilize e&isting soil materialin the theater of operations requires an as-sessment of the mission, enemy, terrain,

troops 'and equipment(, and time available'"E-(.

"ission. )hat type of facility is to beconstructed*road, airfield, or build-ing foundation+ ow long will thefacility be used 'design life(+Enemy. s the enemy interdictinglines of communications+ f so, howwill it impact on your ability to haul

stabilizing admi&tures delivered toyour construction site+errain, ssess the effect of terrainon the project during the construction

phase and over the design life of the

facility. s soil erosion li!ely+ f so,what impact will it have+ s there aslope that is li!ely to become unstable+roops 'and equipment(. %o you haveor can you get equipment needed toperform the stabilization operation+ime available. %oes the tactical situa-

tion permit the time required to stabi-lize the soil and allow the stabilizedsoil to cure 'if necessary(+

here are numerous methods by which

soils can be stabilized/ however, all methods fallinto two broad categories. hey are*

"echanical stabilization.0hemical admi&ture stabilization.

Some stabilization techniques use a com-bination of these two methods. "echanical

Soil Stabilization for Roads and Airfields 9-1

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stabilization relies on physical processes tostabilize the soil, either altering the physicalcomposition of the soil 'soil blending( or plac-

ing a barrier in or on the soil to obtain thedesired effect 'such as establishing a sodcover to prevent dust generation(. 0hemicalstabilization relies on the use of an admi&ture

to alter the chemical properties of the soil toachieve the desired effect 'such as using lime toreduce a soil1s plasticity(.

0lassify the soil material using the 2S0S.)hen a soil testing !it is unavailable, classify

the soil using the field identificationmethodology. "echanical stabilizationthrough soil blending is the most economicaland e&pedient method of altering the e&isting

material. )hen soil blending is not feasibleor does not produce a satisfactory soil

material, geote&tiles or chemical admi&turestabilization should be considered. f chemi-cal admi&ture stabilization is beingconsidered, determine what chemical admi&-tures are available for use and any specialequipment or training required to successfully

incorporate the admi&ture.

MECHA%CA' STA#''(AT$%

"echanical stabilization produces by com-paction an interloc!ing of soil-aggregateparticles. he grading of the soil-aggregate

mi&ture must be such that a dense mass isproduced when it is compacted. "echanicalstabilization can be accomplished byuniformly mi&ing the material and then com-pacting the mi&ture. s an alternative,additional fines or aggregates maybe blended

before compaction to form a uniform, well-graded, dense soil-aggregate mi&ture aftercompaction. he choice of methods should be

based on the gradation of the material. nsome instances, geote&tiles can be used to im-

prove a soil1s engineering characteristics 'seeChapter 11).

he three essentials for obtaining aproperly stabilized soil mi&ture are*

3roper gradation. satisfactory binder soil.

3roper control of the mi&ture content.

Soil Stabilization for Roads and Airfields 9-)

o obtain uniform bearing capacity, uniformmi&ture and blending of all materials is es-sential. he mi&ture will normally becompacted at or near 4"0 to obtain satisfac-tory densities.

he primary function of the portion of a

mechanically stabilized soil mi&ture that isretained on a 5umber 677 sieve is to con-tribute internal friction. 3ractically allmaterials of a granular nature that do not sof-ten when wet or pulverize under traffic can beused/ however, the best aggregates are thosethat are made up of hard, durable, angularparticles. he gradation of this portion of themi&ture is important, as the most suitable ag-gregates generally are well-graded fromcoarse to fine. )ell-graded mi&tures arepreferred because of their greater stabilitywhen compacted and because they can be

compacted more easily. hey also havegreater increases in stability with cor-responding increases in density. Satisfactorymaterials for this use include*

0rushed stone.0rushed and uncrushed gravel.Sand.0rushed slag.

"any other locally available materialshave been successfully used, including disin-tegrated granite, talus roc!, mine tailings,

caliche, coral, limeroc!, tuff, shell, slin!ers,cinders, and iron ore. )hen local materialsare used, proper gradation requirements can-

not always be met.

%$TE* f conditions are enco+ntered in,"ic" t"e radation obtained b. blend-in local /aterials is eit"er finer orcoarser t"an t"e secified radation t"esize re2+ire/ents of t"e finer fractionss"o+ld be satisfied and t"e radation of

t"e coarser sizes s"o+ld be nelected!

he portion of the soil that passes a 5um-ber 677 sieve functions as filler for the rest ofthe mi&ture and supplies cohesion. his aidsin the retention of stability during dryweather. he swelling of clay material serves

somewhat to retard the penetration of

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moisture during wet weather. 0lay or dustfrom roc!-crushing operations are commonlyused as binders. he nature and amount ofthis finer material must be carefully con-trolled, since too much of it results in an unac-

ceptable change in volume with change in

moisture content and other undesirableproperties. he properties of the soil binderare usually controlled by controlling the plas-

ticity characteristics, as evidenced by the 88and 3. hese tests are performed on the por-

tion of the material that passes a 5umber 97sieve. he amount of fines is controlled bylimiting the amount of material that maypass a 5umber 677 sieve. )hen the stabi-lized soil is to be subjected to frost action, this

factor must be !ept in mind when designing thesoil mi&ture.

3ses

"echanical soil stabilization may be used inpreparing soils to function as*

Subgrades.:ases.Surfaces.

Several commonly encountered situationsmay be visualized to indicate the usefulnessof this method. 4ne of these situations occurswhen the surface soil is a loose sand that is in-

capable of providing support for wheeledvehicles, particularly in dry weather. fsuitable binder soil is available in the area, itmay be brought in and mi&ed in the properproportions with the e&isting sand to providean e&pedient all-weather surface for lighttraffic. his would be a sand-clay road. hisalso may be done in some cases to provide a#wor!ing platform$ during constructionoperations. somewhat similar situationmay occur in areas where natural gravelssuitable for the production of a well-gradedsand-aggregate material are not readilyavailable. 0rushed stone, slag, or othermaterials may then be stabilized by the addi-

tion of suitable clay binder to produce asatisfactory base or surface. commonmethod of mechanically stabilizing an e&ist-ing clay soil is to add gravel, sand, or other

granular materials. he objectives here areto*

ncrease the drainability of the soil.ncrease stability.

Reduce volume changes.

0ontrol the undeirable effects associated

with clays.

$bectie

he objective of mechanical stabilization isto blend available soils so that, when properly

compacted, they give the desired stability. ncertain areas, for e&ample, the natural soil ata selected location may have low load-bearing

strength because of an e&cess of clay, silt, orfine sand. )ithin a reasonable distance,suitable granular materials may occur thatmay be blended with the e&isting soils to

mar!edly improve the soil at a much lowercost in manpower and materials than is in-volved in applying imported surfacing.

he mechanical stabilization of soils inmilitary construction is very important. heengineer needs to be aware of the possibilities

of this type of construction and to understandthe principles of soil action previouslypresented. he engineer must fully inves-tigate the possibilities of using locallyavailable materials.

'i/itations

)ithout minimizing the importance ofmechanical stabilization, the limitations ofthis method should also be realized. heprinciples of mechanical stabilization havefrequently been misused, particularly inareas where frost action is a factor in thedesign. ;or e&ample, clay has been added to#stabilize$ soils, when in reality all that wasneeded was adequate compaction to provide astrong, easily drained base that would not be

susceptible to detrimental frost action. nunderstanding of the densification that canbe achieved by modern compaction equip-ment should prevent a mista!e of this sort.Somewhat similarly, poor trafficability of asoil during construction because of lac! offines should not necessarily provide an e&cuse


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for mi&ing in clay binder. he problem may

possibly be solved by applying a thin surfacetreatment or using some other e&pedientmethod.

Soil #ase Re2+ire/ents

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local materials will give satisfactory service,even though they do not meet the stated re-quirements. "any stabilized mi&tures havebeenmade using shell, coral, soft limestone, cinders,marl, and other materials listed ear-lier. Reliance must be placed on*

E&perience.

n understanding of soil action.he qualities that are desired in thefinished product.4ther factors of local importance in

proportioning such mi&tures in thefield.

Blending. t is assumed in this discussionthat an e&isting subgrade soil is to be stabi-lized by adding a suitable borrow soil toproduce a base course mi&ture that meets thespecified requirements. he mechanical

analysis and limits of the e&isting soil willusually be available for the results of the sub-grade soil survey 'see Chapter 3). Similarinformation is necessary concerning the bor-row soil. he problem is to determine the

proportions of these two materials thatshould be used to produce a satisfactory mi&-ture. n some cases, more than two soils must

be blended to produce a suitable mi&ture.owever, this situation is to be avoided when

possible because of the difficulties frequently

encountered in getting a uniform blend ofmore than two local materials. rial com-

binations are usually made on the basis of themechanical analysis of the soil concerned. nother words, calculations are made to deter-mine the gradation of the combined materialsand the proportion of each component ad-

justed so that the gradation of thecombination falls within specified limits. he3 of the selected combination is then deter-mined and compared with the specification.f this value is satisfactory, then the blendmay be assumed to be satisfactory, providedthat the desired bearing value is attained. fthe plasticity characteristics of the first comb-ination are not within the specified limits,additional trials must be made. he propor-tions finally selected then may be used in the fieldconstruction process.

Numerical Proportioning. he process ofproportioning will now be illustrated by a

numerical e&ample 'see Table %-1 pa&e %-6).wo materials are available, material : in the

roadbed and material from a nearby borrowsource. he mechanical analysis of each ofthese materials is given, together with the 88and 3 of each. he desired grading of thecombination is also shown, together with the

desired plasticity characteristics.

Specified Gradation. 3roportioning oftrial combinations may be done arithmetical-ly or graphically. he first step in usingeither the graphical or arithmetical method isto determine the gradation requirements.B9-inch sieve while material : has C6percent passing the same sieve. 4nce plotted,a line is drawn across the graph, connectingthe percent passing of material with thepercent passing of material : for each sievesize.

%$TE* Since bot" /aterials A and # "ad100 ercent assin t"e l-inc" siee it

,as o/itted fro/ t"e ra" and ,illnot affect t"e res+lts!

"ar! the point where the upper and lower

limits of the gradation requirements intersect


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the line for each sieve size. n Fi&ure %-1 theallowable percent passing the 5umber 9 sieveranges from >= to D= percent passing. hepoint along the 5umber 9 line at which D=percent passing intersects represents 6 per-cent material and ? percent material :.he >= percent passing intersects the 5um-

ber 9 line at ?A percent material and ?percent material :. he acceptable ranges ofmaterial to be blended with material : isthe widest range that meets the gradation re-

quirements for all sieve sizes. he shaded

area of the chart represents the combinationsof the two materials that will meet thespecified gradation requirements. heboundary on the left represents the combina-tion of 99 percent material and =D percentmaterial :. he position of this line is fi&ed

by the upper limit of the requirement relatingto the material passing the 5umber 677 sieve

'?= percent(. he boundary on the right rep-resents the combination of 6? percentmaterial and CA percent material :. hisline is established by the lower limit of the re-

quirement relative to the fraction passing the5umber 97 sieve '?= percent(. ny mi&turefalling within these limits satisfies the grada-

tion requirements. ;or purposes ofillustration, assume that a combination of >7

percent material and C7 percent material

Soil Stabilization for Roads and Airfieids 9-7

: is selected for a trial mi&ture, similardiagram can be prepared for any two soils.

Arithmetical Proportioning. Record theactual gradation of soils and : in theirrespective columns '0olumns ? and 6, Fi&ure%-). verage the gradation limits and recordin the column labelled FSF. ;or e&ample, the

allowable range for percent passing a >B-inch

sieve in a ?-inch minus base course is =7 to 7

percent. he average, =7G7B6, is D= percent.s shown in Fi&ure %- S for >B inch is D=.

5e&t, determine the absolute value of S-and S-: for each sieve size and record in thecolumns labelled #'S-(# and # 'S-:(, res-pectively. Sum columns 'S-( and ' S-:(.o determine the percent of soil in the finalmi&, use the formula*

n the e&ample in Fi&ure %-*

?7> ?7>H & ?77I H 9>.=I

?>9 J ?7> 6>C

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he percent of soil : in the final mi& can bedetermined by the formulaK

or

?77I - I H I:

%$TE* f t"ree or /ore soils are to beblended t"e for/+la ,o+ld be

I0 H

his formula can be further e&panded asnecessary.

"ultiply the percent passing each sieve forsoil by the percentage of soil in the finalmi&/ record the information in column 9 'seeFi&ure %- pa&e %-7) Repeat theprocedurefor soil : and record the information incolumn = 'see Fi&ure %- pa&e %- 7).0ompletethe arithmetical procedure by addingcolumns 9 and = to obtain the percent passing eachsieve in the blended soil.

:oth the graphical and arithmeticalmethods have advantages and disad-vantages. he graphical method eliminatesthe need for precise blending under field con-ditions and the methodology requires lesseffort to use, ts drawbac! becomes very com-ple& when blending more than two soils. hearithmetical method allows for more precise

blending, such as mi&ing at a batch plant, andit can be readily e&panded to accommodatethe blending of three or more soils. t has thedrawbac! in that precise blending is often un-attainable under field conditions. hisreduces the quality assurance of the perfor-mance of the blended soil material.

Plasticity Requirements. method ofdetermining the 3 and 88 of the combinedsoils serves as a method to indicate if theproposed trial mi&ture is satisfactory, pend-ing the performance of laboratory tests. hismay be done either arithmetically or graphi-cally. graphical method of obtaining these

Soil Stabilization for Roads and Airfields 9-:

appro&imate values is shown in Fi&ure %-3.he values shown in Fi&ure %-3 require addi-tional e&planation, as follows. 0onsider =77pounds of the mi&ture tentatively selected '>7percent as material and C7 percent asmaterial :(. 4f this =77 pounds, ?=7 poundsare material and >=7 pounds material :.

)ithin the ?=7 pounds of material , thereare ?=7 '7.=6( H C pounds of material passingthe 5umber 97 sieve. )ithin the >=7 poundsof material :, there are ?=7 '7.7=( H ?C.=pounds of material passing the 5umber 97sieve. he total amount of material passingthe 5umber 97 sieve in the =77 pounds of

blend H CJ ?C.=H A=.= pounds, he percent-age of this material that has a 3 of A'material ( is 'CBA=.=( ?77H 6. s shown inFi&ure %-3 the appro&imate 3 of the mi&tureof >7 percent material and C7 percentmaterial : is C.9 percent. :y similar reason-

ing, the appro&imate 88 of the blend is 6,9percent. hese values are somewhat higherthan permissible under the specification. nincrease in the amount of material : willsomewhat reduce the 3 and 88 of the com-bination.

ield Proportioning. n the field, thematerials used in a mechanically stabilizedsoil mi&ture probably will be proportioned byloose volume. ssume that a mi&ture incor-porates C= percent of the e&isting subgradesoil, while 6= percent will be brought in from

a nearby borrow source. he goal is to con-struct a layer that has a compacted thic!nessof D inches. t is estimated that a loose thic!-ness of inches will be required to form theD-inch compacted layer. more e&actrelationship can be established in the field asconstruction proceeds, 4f the inches loosethic!ness, C= percent 'or 7.C='( H D inches(will be the e&isting soil, he remainder of themi& will be mi&ed thoroughly to a depth of inches and compacted by rolling. heproportions may be more accurately control-led by weight, if weight measurements can be made

under e&isting conditions.

;aterroofinhe ability of an airfield or road to sustain

operations depends on the bearing strength ofthe soil. lthough an unsurfaced facility maypossess the required strength when initiallyconstructed, e&posure to water can result i n a

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primary means of waterproofing soils whengrading, compaction, and drainage practicesare insufficient. 2se of geote&tiles is dis-cussed in detail in Chapter 11.

CHEMCA' A&Mt+re!

)hen selecting a stabilizer additive, thefactors that must be considered are the*

ype of soil to be stabilized.3urpose for which the stabilized layerwill be used.

ype of soil quality improvementdesired.Required strength and durability ofthe stabilized layer.0ost and environmental conditions.

Table %- li't' stabilization methods most

suitable for specific applications. o deter-mine the stabilizing agent's( most suited to a

particular soil, use the gradation triangle inFi&ure %-+ pa&e %-1 to find the area thatcor-responds to the gravel, sand, and fine contentof the soil. ;or e&ample, soil % has the follow-ing characteristicsK


)ith A= percent passing the 5umbersieve, the 3 is ?9.)ith ?9 percent passing the 5umber677 sieve, the 88 is 6?.

herefore the soil is = percent gravel, ?percent sand, and ?9 percent fines. Fi&ure %-+pa&e %-1 shows this soil in rea ?0.

Table %-3 pa&e %-13 shows that thestabilizing agents recommended for rea ?0soils include bituminous material, portlandcement, lime, and lime-cement-fly ash. nthis e&ample, bituminous agents cannot beused because of the restriction on 3, but anyof the other agents can be used if available.

Ce/ent

0ement can be used as an effective stabi-lizer for a wide range of materials. n general,however, the soil should have a 3 less than>7. ;or coarse-grained soils, the percentpassing the 5umber 9 sieve should be greaterthan 9= percent.

f the soil temperature is less than 97degrees ;ahrenheit and is not e&pected to in-crease for one month, chemical reactions willnot occur rapidly. he strength gain of the ce-

ment-soil mi&ture will be minimal. f theseenvironmental conditions are anticipated,

the cement may be e&pected to act as a soilmodifier, and another stabilizer might be con-sidered for use. Soil-cement mi&tures shouldbe scheduled for construction so that suffi-cient durability will be gained to resist anyfreeze-thaw cycles e&pected.

3ortland cement can be used either tomodify and improve the quality of the soil orto transform the soil into a cemented mass,which significantly increases its strength anddurability. he amount of cement additive

depends on whether the soil is to be modifiedor stabilized. he only limitation to theamount of cement to be used to stabilize ormodify a soil pertains to the treatment of the

base courses to be used in fle&ible pavementsystems. )hen a cement-treated base coursefor ir ;orce pavements is to be surfaced with

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asphaltic concrete, the percent of cement byweight is limited to 9 percent.

Modification. he amount of cement re-quired to improve the quality of the soilthrough modification is determined by thetrial-and-error approach. o reduce the 3 ofthe soil, successive samples of soil-cement

mi&tures must be prepared at different treat-ment levels and the 3 of each mi&turedetermined.

he minimum cement content that yieldsthe desired 3 is selected, but since it wasdetermined based on the minus 97 fraction ofthe material, this value must be adjusted to

find the design cement content based on totalsample weight e&pressed as*

H ?77:c

where*

H design cement content, percent of

total weight of soil

:Hpercent passing 5umber 97 sieve,e&pressed as a decimal

cHpercent of cement required to obtainthe desired 3 of minus 5umber 97material, e&pressed as a decimal


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f the objective of modification is to im-prove the gradation of granular soil throughthe addition of fines, the analysis should beconducted on samples at various treatmentlevels to determine the minimum acceptable

cement content. o determine the cementcontent to reduce the swell potential of fine-grained plastic soils, mold several samples atvarious cement contents and soa! thespecimens along with untreated specimensfor four days. he lowest cement content that

eliminates the swell potential or reducesthe swell characteristics to the minimum

Soil Stabilization for Roads and Airfields 9-1)

becomes the design cement content. he ce-ment content determined to accomplish soilmodification should be chec!ed to see if itprovides an unconfined compressive strengthgreat enough to qualify for a reduced thic!-

ness design according to criteria established for soilstabilization 'see Table' %-+ an %-5 pa&e %-1+).

0ement-modified soil may be used in frostareas also. n addition to the procedures for

the mi&ture design described above, curedspecimens should be subjected to the ?6

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freeze-thaw cycles test 'omit wire brush por-tion( or other applicable freeze-thaw pro-

cedures. his should be followed by a frost-susceptibility test, determined after freeze-thaw cycling, and should meet the require-ments set forth for the base course. f cement-

modified soil is used as the subgrade, its frostsusceptibility 'determined after freeze-thawcycling( should be used as the basis of thepavement thic!ness design if the reducedsubgrade-strength design method is applied.

Sta#ili(ation. he following procedure is

recommended for determining the design ce-ment content for cement-stabilized soilsK

Step ?. %etermine the classificationand gradation of the untreated soil.he soil must meet the gradation re-quirements shown in Table %-6 beforeit can be used in a reduced thic!nessdesign 'multilayer design(.


Step 6. Select an estimated cementcontent from Table %-7 using the soil

classification.

Step >. 2sing the estimated cementcontent, determine the compactioncurve of the soil-cement mi&ture.

Step 9. f the estimated cement con-tent from step 6 varies by more thanG6 percent from the value in Table'%-8 or %-% pa&e %-16 conductadditional compaction tests, varyingthe cement content, until the valuefrom Table %-8 or %-% pa&e %-16 iswithin 6 percent of that used for themoisture-density test.

%$TE* igure )*+, page )*-, is +sed incon+nction ,it" /a#le )*), page )*-0.T"e ro+ inde> is obtained fro/ ig*ure )*+, page )*- and +sed to enter/a#le )*), page )*-0.

Step =. 3repare samples of the soil-cement mi&ture for unconfined com-pression and durability tests at the drydensity and at the cement contentdetermined in step 9. lso preparesamples at cement contents 6 percentabove and 6 percent below thatdetermined in step 9. he samplesshould be prepared according toTM 5-530 e&cept that when morethan >= percent of the material isretained on the 5umber 9 sieve,

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a 0:R mold should be used toprepare the specimens. 0ure thespecimens for seven days in a humidroom before testing. est three spec-imens using the unconfined com-pression test and subject three spec-imens to durability tests. hese tests

should be either wet-dry tests forpavements located in nonfrost areasor freeze-thaw tests for pavementslocated in frost areas.

Step D. 0ompare the results of theunconfined compressive strength anddurability tests with the require-ments shown in Table' %-+ an %-5.

he lowest cement content thatmeets the required unconfined com-pressive strength requirementand demonstrates the requireddurability is the design content.f the mi&ture should meet thedurability requirements but notthe strength requirements, themi&ture is considered to be amodified soil.

heater-of-operations construction re-quires that the engineer ma!e ma&imum useof the locally available constructionmaterials. owever, locally availablematerials may not lend themselves to


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classification under the 2S0S method. heaverage cement requirements of common lo-cally available construction materials isshown in Table %-10.

'i/e

E&perience has shown that lime reacts withmedium-, moderately fine-, and fine-grainedsoils to produce decreased plasticity, in-creased wor!ability and strength, andreduced swell. Soils classified according tothe 2S0S as '0(, '08(, '"(, '"8(, 'S0(,

'S"(, '

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Modification. he amount of lime requiredto improve the quality of a soil is determinedthrough the same trial-and-error processused for cement-modified soils.

Sta#ili(ation. o ta!e advantage of the

thic!ness reduction criteria, the lime-stabi-lized soil must meet the unconfinedcompressive strengths and durability re-quirements shown in Table' %-+ an %-5pa&e %-1+ respectively.

)hen lime is added to a soil, a com-bination of reactions begins to ta!e placeimmediately. hese reactions are nearly com-

plete within one hour, althoughsubstantial strength gain is not reflectedfor some time. he reactions result in a

change in both the chemical compositionand the physical properties. "ost lime hasa p of about ?6.9 when placed in awater solution. herefore, the p is a goodindicator of the desirable lime content of asoil-lime mi&ture. he reaction that ta!esplace when lime is introduced to a soilgenerally causes a significant change in theplasticity of the soil, so the changes in the38 and the 88 also become indicators ofthe desired lime content. wo methods fordetermination of the initial design lime

content are presented in the following stepsKStep ?. he preferred method is to

prepare several mi&tures at differentlime-treatment levels and determinethe p of each mi&ture after onehour. he lowest lime content pro-ducing the highest p of the soil-limemi&tures is the initial design limecontent. 3rocedures for conducting ap test on lime-soil mi&tures arepresented in " =-=>7. n frost areas,specimens must be subjected to the

freeze-thaw test as discussed in step 6below. n alternate method of deter-mining an initial design lime contentis shown in ;igure A-D, page A-67.Specific values required to use thisfigure are the 3 and the percent ofmaterial passing the 5umber 97 sieve.hese properties are determined fromthe 38 and the gradation test on the

untreated soil for e&pedient construc-tion/ use the amount of stabilizer deter-mined from the p test or Fi&ure %-6pa&e %-0.

Step 6. fter estimating the initial

lime content, conduct a compactiontest with the lime-soil mi&ture. hetest should follow the same pro-cedures for soil-cement e&cept themi&ture should cure no less than onehour and no more than two hours in asealed container before molding.0ompaction will be accomplished infive layers using == blows of a?7-pound hammer having an ?-inchdrop '0; ==(. he moisture densityshould be determined at lime con-tents equal to design plus 6 percentand design plus 9 percent for the

preferred method at design G 6 per-cent for the alternate method, nfrost areas, cured specimens should

be subjected to the ?6 freeze-thawcycles 'omit wire brush portion( orother applicable freeze-thaw pro-cedures, followed by frost sus-ceptibility determinations in stan-dard laboratory freezing tests.;or lime-stabilized or lime-modifiedsoil used in lower layers of the base

course, the frost susceptibility 'deter-mined after freeze-thaw cycling(should meet the requirements for thebase course. f lime-stabilized or lime-modified soil is used as the subgrade,its frost susceptibility 'determinedafter freeze-thaw cycling( should bethe basis of the pavement thic!nessdesign if the reduced subgrade strength designmethod is applied.

Step >. 2niformed compression testsshould be performed it the designpercent of ma&imum density on threespecimens for each lime contenttested. he design value would then

be the minimum lime content yielding

the required strength. 3rocedures forthe preparation of lime-soil specimensare similar to those used for cement-stabilized soils with two e&ceptionsK


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Soil Stabilization for Roads and Airfieds 9-)0

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after mi&ing, the lime-soil mi&tureshould be allowed to mellow for notless than one hour nor more than twohours/ after compaction, each spec-imen should be wrapped securely to

prevent moisture loss and should be

cured in a constant-temperature cham-ber at C> degrees ;ahrenheit G6degrees ;ahrenheit for 6 days. 3ro-cedures for conducting unconfinedcompression tests are similar to thoseused for soil-cement specimens e&ceptthat in lieu of moist curing, the lime-

soil specimens should remain securelywrapped until testing.

Step 9. 0ompare the results of theunconfined compressive tests with the

criteria in Table %-+ pa&e %-1+. hedesign lime content must be the low-est lime content of specimens meetingthe strength criteria indicated.

"ther Additi%es. 8ime may be used as apreliminary additive to reduce the 3 or altergradation of a soil before adding the primarystabilizing agent 'such as bitumen or ce-ment(. f this is the case, then the design limecontent is the minimum treatment level thatwill achieve the desired results. ;or nonplas-tic and low-3 materials in which lime alonegenerally is not satisfactory for stabilization,fly ash may be added to produce the necessary

reaction.

Fl. As"

;ly ash is a pozzolanic material that con-sists mainly of silicon and aluminumcompounds that, when mi&ed with lime andwater, forms a hardened cementitious masscapable of obtaining high compressionstrengths. ;ly ash is a by-product of coal-

fired, electric power-generation facilities.he liming quality of fly ash is highly depend-ent on the type of coal used in powergeneration. ;ly ash is categorized into twobroad classes by its calcium o&ide '0a4( con-tent. hey are*

0lass 0.0lass ;.

Class C! his class of fly ash has a high 0a4content '?6 percent or more( and originatesfrom subbituminous and lignite 'soft( coal.

;ly ash from lignite has the highest 0a4 con-tent, often e&ceeding >7 percent. his typecan be used as a stand-alone stabilizing

agent. he strength characteristics of 0lass0 fly ash having a 0a4 less than 6= percentcan be improved by adding lime. ;urther dis-

cussion of fly ash properties and a listing ofgeographic locations where fly ash is li!ely to befound are in Appeni, .

'lass . his class of fly ash has a low 0a4content 'less than ?7 percent( and originatesfrom anthracite and bituminous coal. 0lass ;fly ash has an insufficient 0a4 content for the

pozzolanic reaction to occur. t is not effective

as a stabilizing agent by itself/ however, whenmi&ed with either lime or lime and cement,the fly ash mi&ture becomes an effectivestabilizing agent.

Lime ly Ash Mi&tures. 8; mi&tures cancontain either 0lass 0 or 0lass ; fly ash. he8; design process is a four-part process thatrequires laboratory analysis to determine theoptimum fines content and lime-to-fly-ashratio.

Step ?. %etermine the optimum fines

content. his is the percentage of flyash that results in the ma&imum den-sity of the soil mi&. %o this by con-ducting a series of moisture-densitytests using different percentages offly ash and then determining the mi&level that yields ma&imum density.he initial fly ash content should beabout ?7 percent based on the weightof the total mi&. 3repare test samplesat increasing increments '6 percent(of fly ash, up to 67 percent. he

design fines content should be 6 per-cent above the optimum fines content.

;or e&ample, if ?9 percent fly ashyields the ma&imum density, thedesign fines content would be ?D per-cent. he moisture density relationwould be based on the ?D percentmi&ture.

Soil Stabilization for Roads and Airfields 9-)1

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Step 6. %etermine the rates of lime tofly ash, 2sing the design fines con-tent and the 4"0 determined in step?, prepare triplicate test samples at8; ratios of ?K>, ?K9, and ?K=. 0ure alltest samples in sealed containers for

seven days at ?77 degrees ;ahrenh-eit .

Step>. Evaluate the test samples forunconfined compressive strength. ffrost is a consideration, subject a setof test samples to ?6 cycles of freeze-thaw durability tests 'refer to ;"=-=>7 for actual test procedures(.

Step 9. %etermine the design 8;ratio. 0ompare the results of the

unconfined strength test andfreeze-thaw durability tests with theminimum requirements found inTable' %-+ an( %-5 pa&e %-1+respectively. he 8; ratio with thelowest lime content that meets therequired unconfined compressivestrength and demonstrates therequired durability is the design 8;content. he treated material must alsomeet frost susceptibility requirementsas indicated in pecial eport 83-7. fthe mi&ture meets the durability

requirements but not the strengthrequirements, it is considered to be amodified soil. f neither strength nordurability criteria are met, a different8; content may be selected and thetesting procedure repeated.

'i/e-Ce/ent-Fl. As" ?'CF@ Mi>t+res!he design methodology for determining the80; ratio for deliberate construction is thesame as for 8; e&cept cement is added in step

6 at the ratio of ? to 6 percent of the design

fines content. 0ement may be used in place ofor in addition to lime/ however, the design

fines content should be maintained.

)hen e&pedient construction is required,use an initial mi& proportion of ? percentportland cement, 9 percent lime, ?D per-cent fly ash, and CA percent soil. "inimum

Soil Stabilization for Roads and Airfields 9-))

unconfined strength requirements 'seeTable %-+ pa&e %-1+) must be met. f testspecimens do not meet strength require-ments, add cement in ?B6 percent incrementsuntil strength is adequate. n frost-suscep-tible areas, durability requirements must also be

satisfied 'see Table %-5 pa&e %-1+).

s with cement-stabilized base coursematerials, 80; mi&tures containing morethan 9 percent cement cannot be used as basecourse material under ir ;orce airfield pave-ments.

#it+/ino+s Materials

ypes of bituminous-stabilized soils are*

Soil bitumen. cohesive soil systemmade water-resistant by admi&ture.

Sand bitumen. system in whichsand is cemented together by bitumi-nous material.

4iled earth. n earth-road systemmade resistant to water absorptionand abrasion by means of a sprayedapplication of slow- or medium-curing

liquid asphalt.

:itumen-waterproofed, mechanicallystabilized soil. system in which twoor more soil materials are blended toproduce a good gradation of particles

from coarse to fine. 0omparativelysmall amounts of bitumen are needed,and the soil is compacted.:itumen-lime blend. system in which

small percentages of lime are blendedwith fine-grained soils to facilitate the

penetration and mi&ing of bitumensinto the soil.

Soil Gradation. he recommended soilgradations for subgrade materials and baseor subbase course materials are shown in Table'%-11 an %-1 respectively. "echani-cal stabilization may be required to bring soil toproper gradation.

/ypes of Bitumen. :ituminous stabiliza-tion is generally accomplished using*

sphalt cement.0utbac! asphalt.sphalt emulsions.

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he type of bitumen to be used depends on- -the type of soil to be stabilized, the method of

construction, and the weather conditions. nfrost areas, the use of tar as a binder should be

avoided because of its high-temperature sus-

ceptibility. sphalts are affected to a lessere&tent by temperature changes, but a grade ofasphalt suitable to the prevailing climateshould be selected.

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preferred, first determine the general type ofaggregate. f the aggregate contains a highcontent of silica, as shown in Fi&ure %-7 pa&e%-5 a cationic emulsion should be used 'seeFi&ure %-8 pa&e %-5.). f the aggregateis acarbonate roc! 'limestone, for e&ample(, an

anionic emulsion should be used.

Fi&ure' %-% an %-10 can be used to find the

mi& design for asphalt cement. hesepreliminary quantities are used for e&pedientconstruction. he final design content of as-phalt should be selected based on the resultsof the "arshall stability test procedure. heminimum "arshall stability recommendedfor subgrades is =77 pounds/ for base courses,C=7 pounds is recommended. f a soil does notshow increased stability when reasonableamounts of bituminous materials are added,the gradation of the soil should be modified oranother type of bituminous material should

be used. 3oorly graded materials may be

improved by adding suitable fines containing

considerable material passing a 5umber 677 sieve.he amount of bitumen required for a given soilincreases with an increase in per-centage of the finer sizes.

Section ! &esin Concets

STR3CT3RA' CATE=$RES

3rocedures are presented for determiningdesign thic!nesses for two structuralcategories of pavement. hey are*

Single-layer."ultilayer.

ypical e&amples of these pavements are in-dicated in Fi&ure %-11.

typical single-layer pavement is a stabi-

lized soil structure on a natural subgrade.he stabilized layer may be mi&ed in place or

premi&ed and later placed over the e&istingsubgrade. waterproofing surface such asmembrane or a single bituminous surface'S:S( or a double bituminous surface treat-ment '%:S( may also be provided. multilayer structure typically consists of atleast two layers, such as a base and a wearingcourse, or three layers, such as a subbase, a

base, and a wearing course. thinwaterproofing course may also be used on

these structures. Single-layer and multi-layer pavement design procedures arepresented for all categories of roads and forcertain categories of airfields as indicated inTable %-15 pa&e %-8.


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:oth single-layer and multilayer pavementstructures may be constructed under eitherthe e&pedient or none&pedient concept. %if-ferent structural designs are provided toallow the design engineer wider latitude ofchoice. owever, single-layer structures areoften associated with e&pedient constructionrather than none&pedient construction, andmulti layers are none&pedient and per-manent. 0ertain considerations should bestudied to determine whether to use a single-layer or mulilayer design under eitherconcept.

he overall concept of design as described

herein can be defined in four basic determina-tions as indicated in Table %-16.

STA#'(E& PAEME%T&ES=% PR$CE&3RE

o use different stabilized materials effec-tively in transportation facilities, the designprocedure must incorporate the advantagesof the higher quality materials. hese ad-vantages are usually reflected in better

performance of the structures and a reductionin total thic!nesses required. ;rom astandpoint of soil stabilization 'not modifica-tion(, recent comparisons of behavior basedon type and quality of material have shownthat stabilization provides definite structuralbenefits. %esign results for airfield and road

Soil Stabilization for Roads and Airfields 9-):

classifications are presented to provideguidance to the designer in determiningthic!ness requirements when using stabi-lized soil elements. he design thic!ness also

provides the planner the option of comparing

the costs of available types of pavement con-struction, thereby providing the beststructure for the situation.

he design procedure primarily incorporatesthe soil stabilizers to allow a reduction ofthic!ness from the conventional fle&ible

pavement-design thic!nesses. hese thic!-ness reductions depend on the properconsideration of the following variablesK

8oad.ire pressure.%esign life.Soil properties.Soil strength.Stabilizer type.Environmental conditions.4ther factors.

he design curves for theater-of-operationsairfields and roads are given for single-layerand multi layer pavements later in this sec-tion.

n the final analysis, the choice of the ad-mi&ture to be used depends on the economics

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and availability of the materials involved.he first decision that should be made iswhether stabilization should be attemptedat all. n some cases, it may be economicalmerely to increase the compaction require-ments or, as a minimum, to resort toincreased pavement thic!ness. f locallyavailable borderline or unacceptablematerials are encountered, definite con-sideration should be given to upgrading anotherwise unacceptable soil by stabilization.

he rapid method of mi& design should beindicative of the type and percentage of stabi-lizer required and the required designthic!ness. his procedure is meant to be afirst-step type of approach and is by no meansconclusive. :etter laboratory tests areneeded to evaluate strength and durabilityand should be performed in specific caseswhere time allows. Estimated time require-ments for conducting tests on stabilizedmaterial are presented in Table %-17. Evenwhen stabilized materials are used, proper

construction techniques and control practices aremandatory.

THCB%ESS &ES=% PR$CE&3RES

he first paragraphs of this section givethe design engineer information concerningsoil stabilization for construction of theater-of-operations roads and airfields. he

information includes procedures for deter-mining soil1s suitability for stabilization anda means of determining the appropriate typeand amount of stabilizer to be used. he finalobjective in this total systematic approach isto determine the required design thic!nesses.%epending on the type of facility and the or

the 0:R of the unstabilized subgrade, thedesign procedure presented in this section al-lows determination of the required thic!nessof an overlying structure that must be con-structed for each anticipated facility.

his basic structural design problem mayhave certain conventional overriding factors,


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such as frost action, that influence this re-quired thic!ness. he decision to stabilize ornot may be based on factors other than struc-tural factors, such as economy, availability ofstabilizer, and time. t must be realized thatsoil stabilization is not a cure for all militaryengineering problems. 3roper use of thismanual as a guide allows, in some cases,reductions in required thic!nesses. heprimary benefit in soil stabilization is that itcan provide a means of accomplishing orfacilitating construction in situations inwhich environmental factors or lac! ofsuitable materials could preclude or seriouslyhamper wor! progress. hrough the properuse of stabilization, marginal soils can oftenbe transformed into acceptable constructionmaterials. n many instances, the quantity ofmaterials required can be reduced andeconomic advantages gained if the cost of

chemical stabilization can be offset by asavings in material transportation costs.

he structural benefits of soil stabilization,shown by increased load-carrying capability,are generally !nown. n addition, increasedstrength and durability also occur withstabilization.

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4n a single-layer road, a thin wearingcourse may be advisable to provide water-

proofing and to offset the effects of tireabrasion.

M+ltila.er

;or each road category, four design curvesare shown 'see Fi&ure' %-16 an %-17 andFi&ure' %-18 an %-1% pa&e %-3+). hesecur-ves indicate the total thic!ness required forpavements incorporating one of the followingcombinations of soil and stabilizerK

8ime and fine-g-rained soils.sphalt and coarse-grained soils.

3ortland cement and coarse-graind soils.

0oarse- and fine-g-rained soils are definedaccording to the 2S0S. he curves presentedin Fi&ure' %-16 an %-17 an Fi&ure'%-18


an %-1% pa&e %-3+ are applicable over arange of subgrade 0:R values.

ndividual layer thic!ness can be ac-complished using Table %-1% pa&e %-35. histable indicates minimum base and wearingcourse thic!ness requirements for road 0las-ses through E. "inimum surface coursethic!ness requirements are indicated for abase course with a strength of =7 to ?77 0:R.f a stabilized soil layer is used as a subbase,the design base thic!ness is the total thic!-ness minus the combined thic!ness of baseand wearing courses. f a stabilized layer isused as a base course over an untreated sub-

grade, the design base thic!ness is the totalthic!ness minus the wearing course thic!-ness. he following flow diagram showsthese proceduresK

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Reduced thic!ness design factors, 'see-able A-67 and ;igure A-67, page A->D ( should

be applied to conventional design thic!nesswhen designing for permanent and none&-

pedient road and airfield design. he use ofstabilized soil layers within a fle&ible pave-ment provides the opportunity to reduce theoverall thic!ness of pavement structure re-quired to support a given load. o design apavement containing stabilized soil layers re-

quires the application of equivalency factorsto a layer or layers of a conventionallydesigned pavement. o qualify for applicationof equivalency factors, the stabilized layermust meet appropriate strength anddurability requirements set forth in TM5-8-+/AFM 88-7 Chapter +. nequivalen-cy factor represents the number of inches of aconventional base or subbase that can bereplaced by ? inch of stabilized material.Equivalency factors are determined from*

Table %-0 for bituminous stabilized

materials.Fi&ure %-0 pa&e %-36 for materialsstabilized with cement, lime, or acombination of fly ash mi&ed withcement or lime.

Selection of an equivalency factor from thetabulation depends on the classification ofthe soil to be stabilized. Selection of an

equivalency factor from Fi&ure %-0 pa&e%-36 requires that the unconfined compres-sive strength, determined according to S"%?D>>, is !nown. Equivalency factors aredetermined from Fi&ure %-0 pa&e %-36 forsubbase materials only. he relationship es-tablished between abase and a subbase is 6K?.herefore, to determine an equivalency factorfor a stabilized base course, divide the sub-

base factor from Fi&ure %-0 pa&e %-36 by 6.

See TM 5-330/AFM 86-3 !olu"e ## forcon-ventional design procedures.


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ARFE'&SSpecific procedures for determining the

total andBor layer thic!nesses for airfields arediscussed in the following paragraphs. hemore e&pedient methods are shown first, fol-lowed by more elaborate procedures.

irfields are categorized by their position onthe battlefield, the runway length, and thecontrolling aircraft. Table %-1 lists aircraftcategories.

Sinle-'a.er%esign curves for single-layer airfield con-

struction are in Fi&ure' %-1 throu&h %-8pa&e' %-38 throu&h %-++. n thesefigures

the controlling aircraft and design life incycles 'one cycle is one ta!eoff and one land-ing( are indicated for each airfield cate-gory. he design curves are applicable for alltypes of stabilization over a range of subgradestrengths up to a ma&imum above which

stabilization would generally be unwar-ranted if the indicated material subgradestrength could be maintained. %esign curvesare presented for typical theater-of-opera-tions gross weights for the controlling aircraftcategory. ;or a single-layer facility, a thinwearing course may provide waterproofing orminimize abrasion resulting from aircrafttires. he following flow diagram indicatesthese proceduresK


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Soil Stabilization for Roads and Airfields 9-6:

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M+ltila.er

n the design of multilayer airfields, it isfirst necessary to determine the total designthic!ness based on conventional fle&iblepavement criteria. hen an appropriatereduction factor is applied for the particularsoil-stabilizer combination anticipated foruse. %eterminations of individual layer

thic!ness finalizes the design. 0onventional

fle&ible pavement design curves and proce-dures may be found in TM 5-330/AFM 86-3!olu"e ##. fter total thic!ness has beendetermined, a reduction factor is applied 'seeTable %- or %-3 pa&e %-+5).ndividuallayer thic!nesses can be determined usingTable %-+ pa&e %-+6 and procedures indi-

cated for multi layer roads. he following flowdiagram indicates these design proceduresK


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E percent is re-

quired to produce a p of ?6.9. Since the soilclassified as an 'S0(, an estimated cementcontent of C percent is selected from TableA-C, pa&e A-?=. he fly ash ratio is 9 percentlime, ? percent cement, ?D percent fly ash,and CA percent soil. he characteristics of alladditives are then reviewed, and because ofpredicted cool weather conditions, cementstabilization is chosen.

he design thic!ness is then determined.he facility will be designed as a close battle

area >,7771 airfield designed for 967 cycles of a0-?>7 aircraft. o determine the designthic!ness. Fi&ure %-1 pa&e %-7 is used. ;or asubgrade strength of 0:R and interpolatingbetween the ?6=,777- and ?C=,777-pound cur-ves, the required design thic!ness is ?> ?B6inches.


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E>a/le )

he mission is to provide a rear area D(7771airfield facility for 0-= aircraft operating at

>67,777 pounds gross weight. ime andmaterials indicate that a multilayer facilitycan be constructed using none&pedientmethods. site reconnaissance indicates thefollowingK

he natural strength is = 0:R.t has a 3 of =.t has a 88 of >=.;ifteen percent passes the 5umber677 sieve.Si&ty percent is retained on the 5um-ber 9 sieve.he classification is '

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'a minimum of =77 pounds(, it can be deter-mined that the upper subgrade can bestabilized with cutbac! asphalt. n optimumasphalt content of D.= percent is indicated.

he design thic!ness is then determined.

'4nly procedures for determining designthic!ness of a ype runway area will be in-dicated.( Since the airfield is a rear-areaD,7771 facility with the 0-?9? as the control-ling aircraft category and is a multilayerdesign, TM 5-330 Fi&ure -36 is used. sub-grade strength of = 0:R and a designthic!ness of 9= inches is required for a con-ventional pavement. Since soil stabilizationis involved, reduced thic!ness design is al-lowed. Table %-0 pa&e %-35 shows that the

equalizing factor for an asphalt-stabilizedsubbase of a '

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?-!ip equivalent loads and a 0:R of =7/ a 9-inch asphaltic cement pavement and a?7-inch cement-stabilized base are required.

E>a/le 5he mission is to provide an e&pedient tac-

tical support area airfield for the operation ofappro&imately C,777 cycles of ;-90 traffic.he single-layer design is selected. sitereconnaissance reveals the followingK

he natural strength is 9 0:R.t has a 3 of ?6.Eleven percent passes a 5umber 677sieve.

wenty percent retained on a 5um-ber 9 sieve.4rganic material occurs as a trace inthe soil samples.

0limatological data indicate a trend forsubfreezing weather, and full traffic must beapplied immediately upon completion. 4r-dinarily, based on information from Fi&ure%-+ pa&e %-1 an( Table %-3 pa&e%-13either cement, lime, or fly ash stabilizationwould be the appropriate agent for this situa-tion and the soil would classify as an 'S)-S"(

borderline. )ith the constraints on curingtimes, soil stabilization would not be the ap-

propriate method of construction. nothermeans, possibly landing mats, must be con-sidered for the successful completion of themission.

E>a/le 7

he mission is to provide an e&pedient0lass E road between two organizational tas!forces. he single-layer design is selected.he preliminary site investigation for a por-tion of the road indicates a natural soilstrength of >7 0:R. he design curve for thisroad classification, shows that a >7-0:R soilis adequate for the intended traffic and that itdoes not require any stabilization 'see Fi&ure%-15 pa&e %-3). herefore, no soil samplingor testing is necessary. problem area maylater arise from a reduction of strength, thatis, a large volume of rainfall or a dust problemon this particular road.


THEATER-$F-$PERAT$%S ARFE'&C$%S&ERAT$%S

n the theater of operations, the lac! oftrained personnel, specialized equipment, ortime often eliminates consideration of manylaboratory procedures. he 0:R and special

stabilization tests in particular will not beconsidered for these reasons. s a result,other methods for determining design pave-ment thic!nesses have been developed usingthe 'see TM 5-330/AFM 86-3 !olu"e##).his system is purely e&pedient and shouldnot replace laboratory testing and reducedthic!ness design procedures.

F+nctions of Soil Stabilization

s previously discussed, the three primary

functions of stabilization are*

Strength improvement.%ust control.)aterproofing.

2se of Table %-5 allows the engineer toevaluate the soil stabilization functions asthey relate to different types of theater-of-operations airfields. t is possible to easilysee the uses of stabilization for the traffic ornontraffic areas of airfields. his table,developed from Table %-6 pa&e %-50 shows

the possible functional considerations forsituations where either no landing mat, alight-duty mat, or a medium-duty mat may beemployed. '8anding mats are discussed inTM 5-330/AFM 86-3 !olu"e ## an TM5-33 7.) s an e&ample of the use of this table,consider the construction of the #heavy lift in thesupport area.$

Referring to the traffic areas, a certain min-imum strength is required for unsurfaced-soiloperations 'that is, without a landing mat( orif either the light duty mat '8"( or themedium duty mat '""( is used. f the e&ist-ing soil strength is not adequate, stabilizationfor strength improvement may be consideredeither to sustain unsurfaced operations or to

be a necessary base for the landing mat. ;ur-ther, if no mat is used, stabilization might beneeded only to provide dust control andBor soil

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waterproofing. f a landing mat is used, how-ever, the functions of dust control and soilwaterproofing would be satisfied andstabilization need not be considered in anyevent. 3ossible stabilization functions fornontraffic areas have been shown in a similar

manner. ;or certain airfields, such as the#light lift in the battle area, $ no function forstrength improvement in either traffic or non-

traffic areas is indicated. Such airfields havean requirement of = or more unsurfacedoperations 'see Table %-6 pa&e %-50).Siteselection should be e&ercised in most in-stances to avoid areas of less than a = . ;orcertain airfields, such as the #tactical in thesupport area,# a landing mater improved sur-facing always will be provided. herefore a #nomat$ situation pertains only to the non-

traffic areas.

&esin Re2+ire/entsfor Strent" /roe/ent

)here stabilization for strength improve-ment is considered, certain basic designrequirements, in terms of strength and thic!-ness of a stabilized soil layer on a givensubgrade, must be met. he strength andthic!ness requirements vary depending onthe operational traffic parameters andthe strength of the soil directly beneath the

stabilized soil layer. Since the trafficparameters are !nown for each airfield type,a minimum strength requirement for the sta-

bilized soil layer can be specified for eachairfield based on unsurfaced-soil criteria. ;orany given subgrade condition, the thic!nessof a minimum-strength, stabilized-soil layernecessary to prevent overstress of the sub-grade also can be determined. Table %-7pa&e %-5 gives design requirements for traf-fic and nontraffic areas of different airfieldtypes for which stabilization may be used forstrength improvement. s seen, the mini-

mum-strength requirement in terms of is afunction only of the applied traffic for a par-ticular airfield and is independent of thesubgrade strength. owever, the thic!ness is adirect function of the underlying subgradestrength.

3roper evaluation of the subg-rade is essen-

tial for establishing thic!ness requirements.

n evaluating the subgrade for stabilizationpurposes, a representative strength profilemust be established to a depth that wouldpreclude the possibility of overstress in theunderlying subgrade. his depth variesdepending on the*

irfield.3attern of the profile itself."anner of stabilization.

n this regard, the thic!ness data given inTable %-7 pa&e %-5 can be used also to pro-vide guidance in establishing an adequatestrength profile. ,=771airfield is to be constructed and that a sub-grade evaluation has been made fromwhich a representative profile to a sufficientdepth can be established. 4ne of threegeneral design cases can be considered de-

pending on the shape of the strength profile.

he first case considers constantstrength with depth/ therefore, the re-quired thic!ness is read directly fromTable %-7 pa&e %-5 under the ap-propriate subgrade column. hus,in the e&ample, if a subgrade of is measured, the required thic!ness ofa stabilized soil layer if no landingmat were used would be ? inches.he required minimum strength of

this stabilized soil layer is an of?=. f the light landing mat wereused, a D-inch-thic! layer with a min-imum of ?7 would be required as a

base overlying the subgrade of .

he second case considers an increasein strength with depth/ therefore, the

required thic!ness of stabilization


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may be considerably less than indi-cated in the table. ;or this e&ample,assume that the increases withdepth as shown in ;igure A-6A. sta-

bilized layer can be provided either bybuilding up a compacted base cm top

of the e&isting ground surface or bytreating the in-place soil. :ecause ofthis, each situation represents asomewhat different design problem.

n in-place treatment is analogous toreplacing the e&isting soil to some depth with

an improved quality material. )herestrength increases with depth, the point atwhich thic!ness is compatible with thestrength at that particular point must bedetermined. his point can be determined

graphically simply by superimposing a plot ofthe thic!ness design requirements versussubgrade 'see Table %-7) directly on thestrength profile plot. his procedure isshown in Fi&ure %-%. he depth at which thetwo plots intersect is the design thic!ness re-quirement for a stabilized-soil layer. n thee&ample, a thic!ness of A.= inches 'or say ?7inches( is required.

f a compacted base of a select borrow soil isused to provide a stronger layer on the sub-grade shown in Fi&ure %-% the thic!nessmust again be consistent with the strength atsome depth below the surface of the placed

base-course layer. Since the base-courselayer itself will be constructed to a minimum of ?=, the wea!est point under the placedbase will be at the surface of the e&istingground, or in this instance an of . 2singthis value, Table %-7 gives a thic!ness of ?inches of base course. 0ompaction of the e&-isting ground would be beneficial in terms ofthic!ness requirements if it would increasethe critical subgrade strength to a higher

value. f, for e&ample, the minimum of thee&isting ground could be increased from to?6, the thic!ness of base required would bereduced to ?7 inches 'see Table %-7).

he third case considers a decrease instrength with depth. he strengthprofile shown in Fi&ure %-30 pa&e%-5+ indicates a crust of firm material

over a significantly wea!er zone ofsoil beneath. n this e&ample, the impor-

tance of proper analysis of subgradeconditions is stressed. f strength datawere obtained to less than >7 inches,the adequacy of the design could not

be fully determined.

0onsider again an in-place stabilizationprocess. lthough the strength profile and

design curve intersect initially at a shallowdepth 'about > inches( 'see Fi&ure %-30 pa&e%-5+) the strength profile does not remain tothe right of the design curve. his indicatesthat the design requirement has been satis-fied. he second and final intersection occursat 69 inches. Since there is no indication of afurther decrease in strength with depth, athic!ness of 69 inches is therefore required.

n the case of a compacted base placed on asubgrade that decreases in strength with

depth, the procedure for determining thedesign thic!ness is more difficult. he designthic!ness can be determined by comparingthe strength-depth profile with the designcurve. f the measured at any given depthis less than the minimum requirement shown

by the design curve, a sufficient thic!ness ofimproved quality soil must be placed on thee&isting ground surface to prevent overstress


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the strength actually achieved may well e&-ceed the minimum requirement, noconsideration should be given to reducing the designthic!ness as given in Table %-7 pa&e %-5or as developed by the stated proce-dures.

Section ! &+st Control

EFFECTS $F &3ST%ust can be a major problem during combat

'and training( operations. %ust negatively impactsmorale, maintenance, and safety.E&perience during 4peration %esertShieldBStorm suggests that dust was a majorcontributor to vehicle accidents. t also ac-celerated wear and tear on vehicles andaircraft components.

%ust is simply airborne soil particles. s ageneral rule, dust consists predominantly ofsoil that has a particle size finer than 7.7C9 mm'that is, passing a 5umber 677 sieve(.

he presence of dust can have significantadverse effects on the overall efficiency ofaircraft by*

ncreasing downtime and mainte-nance requirements.Shortening engine life.

at that depth. owever, the thic!ness of base

necessary must be such that the require-ments will be met at all depths. o satisfythis condition, the required thic!ness must beequal to the ma&imum difference, which willoccur at a particular strength value, betweenthe depth indicated by the design curve andthe depth from the strength-depth profile, nthe e&ample shown in Fi&ure %-30 this ma&-imum difference occurs at an of ?6. hedifference is ?7 inches, which is the requiredthic!ness for an improved quality base.

he same procedures described for adecrease in strength with depth can be usedto derive the strength and thic!ness require-ments for a base course under either an 8" or"". he thic!ness design requirementsgiven herein are for stabilized soil layershaving a minimum strength property to meetthe particular airfield traffic need. lthough


Reducing visibility.

ffecting the health and morale ofpersonnel.

n addition, dust clouds can aid the enemy byrevealing positions and the scope of opera-tions.

&3ST F$RMAT$%

he presence of a relative amount of dust-size particles in a soil surface does notnecessarily indicate a dust problem nor theseverity of dust that will result in various

situations. Several factors contribute to thegeneration, severity, and perpetuity of dustfrom a potential ground source. hese in-clude*

4verall gradation."oisture content.%ensity and smoothness of theground surface.

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3resence of salts or organic matter,vegetation, and wind velocity anddirection.

ir humidity.

)hen conditions of soil and environment

are favorable, the position of an e&ternal forceto a ground surface generates dust that e&istsin the form of clouds of various density, size,and height above the ground. n the case ofaircraft, dust may be generated as a result oferosion by propeller wash, engine e&haustblast, jet-blast impingement, and the draft ofmoving aircraft. ;urther, the !neading andabrading action of tires can loosen particlesfrom the ground surface that may become air-borne.

4n unsurfaced roads, the source of dust

may be the roadway surface. Lehicle trafficbrea!s down soil structure or abrades gravelbase courses, creating fine-grained particlesthat readily become airborne when traffic!ed.

&3ST PA''ATES

he primary objective of a dust palliative isto prevent soil particles from becoming air-

borne. %ust palliative may be required forcontrol of dust on nontraffic or traffic areas or

both. f a prefabricated landing mat,membrane, or conventional pavement surfac-ing is used in the traffic areas of an airfield,the use of dust palliative would be limited tonontraffic areas. ;or nontraffic areas, a pal-liative is needed that can resist the ma&imumintensity of air blast impingement by anaircraft or the prevailing winds. )here dustpalliative provide the necessary resistanceagainst air impingement, they may be totallyunsuitable as wearing surfaces. n impor-tant factor limiting the applicability of a dust

palliative in traffic areas is the e&tent of sur-face rutting that will occur under traffic. lfthe bearing capacity allows the soil surface to

rut under traffic, the effectiveness of a shal-low-depth palliative treatment could bedestroyed rapidly by brea!up and subsequentstripping from the ground surface. Some pal-liatives tolerate deformations better thanothers, but normally ruts ?@ inches deepresult in the virtual destruction of any thinlayer or shallow depth penetration dust pal-liative treatment.

he success of a dust-control programdepends on the engineer1s ability to match adust palliative to a specific set of factors af-fecting dust generation. hese factorsinclude*

ntensity of area use.

opography.Soil type.Soil surface features.0limate.

ntensit. of Area 3se

reas requiring dust-control treatmentsshould be divided into traffic areas based onthe e&pected amount of traffic. he threeclasses of traffic areas are*

5ontraffic.4ccasional traffic.

raffic.

Nontraffic Areas. hese areas requiretreatment to withstand air-blast effects fromwind or aircraft operations and are not sub-jected to traffic of any !ind. ypicalnontraffic areas include*

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Shoulders, hover lanes, and peri-pheral areas of heliports and heli-pads.

5ontraffic areas where occasionaltraffic becomes necessary.

/raffic Areas. reas subjected to regularchannelized traffic by vehicles, aircraft, orpersonnel. 3roperly treated traffic areasresist the effects of air blasts from fi&ed- orrotary-wing aircraft. ypical traffic areas in-cludeK

Roadways and vehicle par!ing areas.)al!ways.4pen storage areas.0onstruction sites.Runways, ta&iways, shoulders, over-runs, and par!ing areas of airfields.over lanes and landing and par!ing

pads of heliports.an! trails.

Toora".

%ust palliative for controlling dust on flatand hillside areas are based on the e&pectedtraffic, but the specific palliative selected may

be affected by the slope. ;or e&ample, a liquidpalliative may tend to run off rather thanpenetrate hillside soils, which degrades thepalliative1s performance.

%ivide the area to be treated into flat andhillside areas. ;lat is defined as an averageground slope of = percent or less, whilehillside refers to an average ground slopegreater than = percent. 3articular areas canbe given special attention, if required.

Soil T.e

Soil type is one of the !ey features used todetermine which method and material should

be used for dust control. Soils to be treated fordust control are placed into five generaldescriptive groupings based on the 2S0S.hey are*

Silts or clays 'high 88( 'types '0(,'4(, and '"((.Silts or clays 'low 88( 'types '"8(,'08(, '"8-08(, and '48((.


Sands or gravels 'with fines( 'types'S"(, 'S0(, 'S"-S0(, '

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during the dry season when the relativehumidity drops below >7 percent.

&3ST-C$%TR$' METH$&S

he four general dust-control-treatmentmethods commonly used are*

gronomic.Surface penetrant.dmi&.Surface blan!et.

Arono/ic

his method consists of establishing,promoting, or preserving vegetative cover toprevent or reduce dust generation from e&-posed soil surfaces. Legetative cover is oftenconsidered the most satisfactory form of dustpalliative. t is aesthetically pleasing,

durable, economical, and considered to bepermanent. Some agronomic approachesto dust control are suitable for theater-of-operations requirements. 3lanning construc-tion to minimize disturbance to the e&istingvegetative cover will produce good dust-palliative results later.

gronomic practices include the use of*

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#it+/ens! 0onventional types of bitu-minous materials that may be used for dustpalliative include*

0utbac! asphalts.

Emulsified asphalts.Road tars.

sphaltic penetrative soil binder'3S:(.

hese materials can be used to treat bothtraffic and nontraffic areas. ll bituminousmaterials do not cure at the same rate. hisfact may be of importance when they are

being considered for use in traffic areas. lso,

bituminous materials are sensitive toweather e&tremes. 2sually bituminousmaterials impart some waterproofing to thetreated area that remains effective as long as

the treatment remains intact 'for e&ample, asplaced or as applied(. :ituminous materialsshould not be placed in the rain or when rainis threatening.

cutbac! asphalt 'cutbac!s( is a blend ofan asphalt cement and a petroleum solvent.hese cutbac!s are classified as R0, mediumcuring '"0(, and slow curing 'S0(, dependingon the type of solvent used and its rate ofevaporation. Each cutbac! is further graded

by its viscosity. he R0 and S0 grades of C7and 6=7, respectively, and "0 grades of >7,C7, and 6=7 are generally used. Regardless ofclassification or grade, the best results are ob-

tained by preheating the cutbac!. Sprayingtemperatures usually range from ?67 to >77degrees ;ahrenheit. he actual range for aparticular cutbac! is much narrower andshould be requested from the supplier at thetime of purchase. he user is cautioned thatsome cutbac!s must be heated above theirflash point for spraying purposes/ therefore,no smo!ing or open flames should be per-mitted during the application or the curing of

the cutbac!. he "0->7 grade can besprayed without being heated if the tempera-ture of the asphalt is 7 degrees ;ahrenheitor above. slightly moist soil surface assistspenetration. he curing time for cutbac!svaries with the type. 2nder favorable ground

temperature and weather conditions, R0cures in ? hour, "0 in > to D hours, and S0 in


? to > days. n selecting the material for use,local environmental protection regulationsmust be considered.

sphalt emulsions 'emulsions( are a blendof asphalt, water, and an emulsifying agent.

hey are available either as anionic orcationic emulsions. he application of emul-sions at ambient temperatures of 7 degrees;ahrenheit or above gives the best results.Satisfactory results may be obtained belowthis temperature, especially if the applicationis made in the morning to permit the warmingeffects of the afternoon sun to aid in curing.Emulsions should not be placed at tempera-tures below =7 degrees ;ahrenheit.Emulsions placed at temperatures belowfreezing will freeze, producing a substandard

product. ;or best results in a freezing en-

vironment, emulsions should be heated tobetween C= and ?>7 degrees ;ahrenheit. hetemperature of the material should never e&-ceed the upper heating limit of ?= degrees;ahrenheit because the asphalt and waterwill separate 'brea!(, resulting in materialdamage. Emulsions generally cure in about hours. he slow setting 'SS( anionic emul-sions of grades SS-? and SS-lh may be dilutedwith ? to = or more parts water to one partemulsified asphalt by volume before using.s a general rule, an application of > partswater to ? part emulsion solution is satisfac-

tory. he slow-setting cationic emulsions orgrades cationic slow setting '0SS(-? and 0SS-?h are easiest to use without dilution. fdilution is desired, the water used must befree of any impurities, minerals, or salts thatmight cause separation 'brea!ing( of theemulsion within the distribution equipment.

Road tars 'Rs( 'tars( are viscous liquidsobtained by distillation of crude tars obtained

from coal. ars derived from other basicmaterials are also available but are not nor-mally used as soil treatments. ars aregraded by viscosity and are available ingrades ranging from ? to ?6. hey are alsoavailable in the road tar cutbac! 'R0:( form

of viscosity grades = and D and in the emul-sified form. ar emulsions are difficult toprepare and handle, he low-viscositygrades R-? and R-6 and the R0: grades

can be applied at temperatures as low as D7

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degrees ;ahrenheit without heating. he tarcutbac!s generally have better penetratingcharacteristics than asphalts and normallycure in a few hours. ars produce e&cellentsurfaces, but curing proceeds very slowly.

Several days or even wee!s may be required

to obtain a completely cured layer. ars aresusceptible to temperature changes and maysoften in hot weather or become brittle in coldweather.

3S:, a commercial product, is a specialliquid asphalt composed of a high penetrationgrade of asphalt and a solvent blend of!erosene and naphtha. t is similar in char-acter to a standard low-viscosity, medium-

7.>> to 7.= gallon per square yard. hematerial may be diluted for spraying using 9parts water to ? part concentrate. hismaterial is primarily suited for dry sandysoils/ it provides unsuitable results whenused on silty and clayey soils.

8ignin is a by-product of the manufactureof wood pulp. t is soluble in water and there-fore readily penetrates the soil. ts volubilityalso ma!es it susceptible to leaching from the

soil/ thus, application is repeated as neces-sary after rainfall. 8ignin is readily available

in the continental 2nited States and certainother sections of the world. t is useful inareas where dust control is desirable for short

curing liquid asphaltNbut it differs in many

specific properties. he 3S: is suitable for

application to soils that are relatively imper-vious to conventional liquid asphalts andemulsion systems. Silts and moderately plas-tic clays 'to a 3 of ?=( can be treatedeffectively. 0uring time for the 3S: is D to?6 hours under favorable ground tempera-ture and weather conditions . 4nhigh-plasticity solids 'with a 3 greater than?=(, the material remains on the surface as anasphalt film that is tac!y at a groundtemperature of appro&imately ?77 degrees;ahrenheit and above. he 3S: must beheated to a temperature between ?>7 to ?=7

degrees ;ahrenheit to permit spraying with anasphalt distributor.

Resins. hese dust palliative may be usedas either surface penetrants or surfaceblan!ets. hey have a tendency to eitherpenetrate the surface or form a thin surface

periods of time/ it is not recommended for usewhere durability is an important factor. he

recommended application rate is ? gallon per squareyard of a resinous solution of percent solid ligninsulphite.

0oncrete curing compounds can be used to

penetrate sands that contain little or no siltsor clays. his material should be limited toareas with no traffic. he high cost of thismaterial is partly offset by the low applicationrate required '7.? to 7.6 gallon per squareyard(. Standard asphalt pressure dis-tributors can be used to apply the resin/however, the conventional spray nozzlesshould be replaced with nozzles with smalleropenings to achieve a uniform distribution at

the low application rate.

Salts. Salts in water emulsions have beenused with varying success as dust palliative.

film depending on the type of resin used, the %ry calcium chloride '0a0?

soil type, and the soil condition. hematerials are normally applicable to nontraf-fic areas and occasional-traffic areas whererutting will not occur. hey are not recom-mended for use with silts and clays.

Resin-petroleum-water emulsions arequite stable and highly resistant to weather-ing. feature of this type of dust palliative isthat the soil remains readily permeable towater after it is treated. his type of productis principally manufactured under the tradename 0ohere&. pplication rates range from

6 ( is deliquescentand is effective when the relative humidity isabout >7 percent or greater. soil treatedwith calcium chloride retains more moisturethan the untreated soil under comparable

drying conditions. ts use is limited tooccasional-traffic areas, Sodium chloride'5a0?( achieves some dust control by retain-ing moisture and also by some cementingfrom salt crystallization. :oth calciumchloride and sodium chloride are soluble inwater and are readily leached from the soilsurface/ thus, frequent maintenance is re-quired. 0ontinued applications of salt


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solutions can ultimately build up a thin,crusted surface that will be fairly hard andfree of dust. "ost salts are corrosive to metaland should not be stored in the vehicle usedfor application. "agnesium chloride

be applied with an asphalt distributor."i&ing equipment that can be used in-cludes*

Rotary tillers.Rotary pulverizer-mi&ers.

'"g0?6 ( controls dust on gravel roads with

trac!ed-vehicle traffic. :est results can bee&pected in areas with occasional rainfall orwhere the humidity is above >7 percent. hedust palliative selected and the quantity usedshould not e&ceed local environmental protec-tion regulations.

!ater. s a commonly used 'but very tem-porary( measure for allaying dust, a soilsurface can be sprin!led with water. s longas the ground surface remains moist or damp,soil particles resist becoming airborne.%epending on the soil and climate, frequent

treatment may be required. )ater shouldnot be applied to clay soil surfaces in suchquantity that puddles forms since a muddy or

slippery surface may result where the soilremains wet.

Ad/i>

he admi& method involves blending thedust palliative with the soil to produce auniform mi&ture. his method requires moretime and equipment than either the penetra-tion or surface blan!et methods, but it has the

benefit of increasing soil strength.

5ormally, a minimum treatment depth of 9inches is effective for traffic areas and > in-ches for other areas. he admi&ture can bemi&ed in place or off site. ypical admi&turedust palliative include*

3ortland cement.ydrated lime.:ituminous materials.

2n*Place Admi&ing. n-place admi&ing isthe blending of the soil and a dust palliative

on the site. he surface soil is loosened 'ifnecessary( to a depth slightly greater thanthe desired thic!ness of the treated layer.he dust palliative is added and blended with

the loosened surface soil, and the mi&ture iscompacted. 3owders may be spread by handor with a mechanical spreader/ liquids should


percent of dry soil

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weight 'for soils having less than >7 percentpassing the 5umber 677 sieve( to D to per-cent 'for soils having more than >7 percentfine-grained soils passing the 5umber 677sieve(. he presence of mica in a soil isdetrimental to the effectiveness of a soil-bituminous material admi&ture. here are

no simple guides or shortcuts for designingmi&tures of soil and bituminous materials.he ma&imum effectiveness of soil-bituminous material admi&tures can usuallybe achieved if the soil characteristics arewithin the following limitsK

he 3 is ?7.he amount of material passing the

5umber 677 sieve is >7 percent byweight.

his data and additional construction data

can be found in " =-66-9. raffic should bedetoured around the treated area un

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