estabilizaciondesuelos

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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 on e or

more 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 du rability or to prevent erosionand dust generation. Regardless of the pur-pose for stabilization, the desired result is thecreation of a soil ma terial or soil system th atwill remain in place under the design use con-d itions for the d esign life of the p roject.

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

This chap ter is aimed at helping to make th ecorrect d ecisions. Many of the p rocedu resoutlined are not precise, but they will “get youin the ball park.” Soils vary th rough out th eworld, and the engineering properties of soilsare equally variable. The key to success insoil stabilization is soil testing. The methodof soil stabilization selected should be verifiedin the laboratory before construction andpr eferably before specifying or ord eringmaterials.

Section I. Methods of Stabilization

BASIC CONSIDERATIONS

Decid ing to stabilize existing soil materialin the theater of operations requires an as-sessm ent of the m ission, enem y, terrain,

troops (and equipment), and time available(METT-T).

Mission. What type of facility is to beconstructed—road, airfield, or build-ing foun dation? How long will thefacility be used (design life)?Enemy. Is the enemy interdictinglines of communications? If so, howwill it impact on your ability to haulstabilizing admixtures delivered toyour construction site?Terrain, Assess the effect of terrainon the project during the constructionphase and over the design life of the

facility. Is soil erosion likely? If so,what impact w ill it have? Is there aslope that is likely to become u nstable?Troops (and equipm ent). Do you haveor can you get equipment needed toperform the stabilization operation?Time available. Does the tactical situa-tion p ermit the time required to stabi-lize the soil and allow the stabilizedsoil to cure (if necessary)?

There are num erous methods by w hich

soils can be stabilized ; how ever, all meth odsfall into two b road categories. They are—

Mechanical stab ilization.Chemical admixture stabilization.

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

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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). Chemicalstabilization relies on the use of an admixture

to alter the chemical prop erties of the soil toachieve the desired effect (such as using limeto reduce a soil’s plasticity).

Classify the soil material using the USCS.When a soil testing kit is unavailable, classifythe soil using the field identificationmethodology. Mechanical stabilizationthrou gh soil blend ing is the most econom icaland expedient method of altering the existingmaterial. When soil blending is not feasibleor does not produce a satisfactory soil

material, geotextiles or chemical admixturestabilization should be considered . If chemi-cal admixture stabilization is beingconsidered, determine what chemical admix-tures are available for use and any specialequipment or training required to successfullyincorporate the admixture.

MECHANICAL STABILILIZATION

Mechanical stabilization produ ces by com-pa ction an interlocking of soil-aggregateparticles. The grading of the soil-aggregate

mixture must be such that a dense mass isproduced when it is compacted. Mechanicalstabilization can be accomplished byuniformly mixing the material and then com-pacting the m ixture. As an alternative,add itional fines or aggregates m aybe blendedbefore compaction to form a uniform, well-graded, dense soil-aggregate mixture aftercompaction. The choice of methods should bebased on the grad ation of the material. Insome instances, geotextiles can be u sed to im-prove a soil’s engineering characteristics (seeChapter 11).

The three essentials for obtaining aproperly stabilized soil mixture are—

Proper gradation.A satisfactory binder soil.Proper control of the mixture content.

To obtain un iform bearing capacity, un iformmixture and blending of all materials is es-sential. The m ixture will normally becompacted at or near OMC to obtain satisfac-tory densities.

The primary function of the portion of a

mechanically stabilized soil mixture that isretained on a N um ber 200 sieve is to con-tribute internal friction. Practically allmaterials of a granular natu re that d o not sof-ten when wet or p ulverize under traffic can beused ; how ever, the best aggregates are thosethat are made up of hard, durable, angularpar ticles. The grad ation of this por tion of themixture is important, as the most suitable ag-gregates generally are well-graded fromcoarse to fine. Well-grad ed m ixtur es arepreferred because of their greater stabilitywh en comp acted and because they can be

compacted more easily. They also havegreater increases in stability with cor-responding increases in d ensity. Satisfactorymaterials for this use include—

Crushed stone.Crushed and uncrushed gravel.Sand.Crushed slag.

Man y other locally ava ilable ma terialshave been successfully used, including disin-tegrated granite, talu s rock, mine tailings,

caliche, coral, limerock, tuff, shell, slinkers,cinders, and iron ore. When local materialsare used, proper gradation requirements can-not always be met.

NO TE: If cond itions are encountered inwh ich the gradation obtained b y blend-ing local materials is either finer orcoarser than the sp ecified gradation, thesize requirem ents of the finer fractionsshould be satisfied and the gradation of the coarser sizes shou ld b e neglected.

The portion of the soil that passes a Num-ber 200 sieve functions as filler for the rest of the mixture and su pp lies cohesion. This aidsin the retention of stability during dryweather. The swelling of clay m aterial servessomewhat to retard the penetration of

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moisture d uring w et weather. Clay or d ustfrom rock-crushing operations are commonlyused as binders. The nature and amou nt of this finer material must be carefully con-trolled, since too mu ch of it results in an un ac-ceptable change in volume with change in

moisture content and other undesirableproperties. The prop erties of the soil binderare usually controlled by controlling the plas-ticity characteristics, as evid enced by th e LLand PI. These tests are performed on the por-tion of the material that p asses a Nu mber 40sieve. The amount of fines is controlled bylimiting the amou nt of material that m aypass a N um ber 200 sieve. When the stabi-lized soil is to be subjected to frost action, thisfactor mu st be kept in mind wh en designingthe soil mixture.

UsesMechanical soil stabilization may be used

in prep aring soils to fun ction as—

Subgrades.Bases.Surfaces.

Several commonly encountered situationsmay be visualized to indicate the usefulnessof this method. One of these situations occurswh en the su rface soil is a loose sand that is in-

capable of providing su pp ort for w heeledvehicles, particularly in dry weather. If suitable bind er soil is available in the area, itmay be brought in and mixed in the p roperproportions with the existing sand to providean exped ient all-w eather su rface for lighttraffic. This w ould be a sand -clay road . Thisalso may be d one in some cases to provide a“working platform” during constructionoperations. A somewhat similar situationmay occur in areas w here natural gravelssuitable for the production of a well-gradedsand-aggregate material are not readilyavailable. Crushed ston e, slag, or othermaterials may then be stabilized by the addi-tion of suitable clay binder to p rod uce asatisfactory base or sur face. A commonmeth od of m echanically stabilizing an exist-ing clay soil is to ad d gravel, sand , or other

granular materials. The objectives here areto—

Increase the d rainability of the soil.Increase stability.Reduce volume changes.Control the undeirable effects associated

with clays.

ObjectiveThe objective of mechanical stabilization is

to blend available soils so that, when properlycompacted , they give the d esired stability. Incertain areas, for examp le, the natur al soil ata selected location may have low load-bearingstrength because of an excess of clay, silt, orfine sand. Within a reasonable distance,suitable granular materials may occur thatmay be blended with the existing soils to

marked ly imp rove the soil at a much lowercost in manpower and materials than is in-volved in app lying imp orted sur facing.

The mechanical stabilization of soils inmilitary construction is very important. Theengineer needs to be aware of the possibilitiesof this type of construction and to und erstandthe principles of soil action previouslypresented. The engineer m ust fully inves-tigate the possibilities of using locallyavailable materials.

LimitationsWithout minimizing the importance of

mechanical stabilization, the limitations of this method should also be realized. Theprinciples of mechanical stabilization havefrequen tly been m isused , particularly inareas w here frost action is a factor in thedesign. For example, clay has been added to“stabilize” soils, when in r eality all that w asneeded w as adequate compaction to provide astrong, easily drained base that would not besusceptible to detrimental frost action. Anunderstanding of the densification that canbe achieved by modern compaction equip-ment should prevent a mistake of this sort.Somewhat similarly, poor trafficability of asoil during construction because of lack of fines should not necessarily provide an excuse




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for mixing in clay binder. The problem m aypossibly be solved by applying a thin surfacetreatment or u sing some other expedientmethod.

Soil Base Requirem entsGrading requirements relative to mechani-

cally stabilized soil mixtures tha t serveas base courses are given in Table 7-3 of TM 5-330 /Air Force Manual (AFM ) 86-3,Volume II. Experience in civil highway con-struction indicates that best results areobtained with this type of mixture if the frac-tion passing the Number 200 sieve is notgreater than two-thirds of the fraction pass-ing the Nu mber 40 sieve. The size of thelargest particles should not exceed two-thirdsof the thickness of the layer in which they areincorporated. The mixture should be well-graded from coarse to fine.

A basic requirement of soil mixtures thatare to be used as base courses is that the PIshou ld not exceed 5. Under certain cir-cumstances, this requirement may be relaxedif a satisfactory bearing ratio is developed,Experience also indicates that un der idealcircumstan ces the LL should not exceed 25.These requirements may be relaxed intheater-of-operations construction. The re-quirements may be lowered to a LL of 35 anda PI of 10 for fully operational a irfields. Foremergency and minimally operational air-fields, the requiremen ts may be lowered to aLL of 45 and a PI of 15, when drainage is good.

Soil Surface RequirementsGrad ing requirem ents for mechanically

stabilized soils that are to be u sed d irectly assurfaces, usu ally un d er emergency cond i-tions, are generally the same as those ind i-cated in Table 7-3 of TM 5-330/AFM 86-3,Volume II. Preference should be given to mix-tures that have a minimum aggregate sizeequal to 1 inch or perhaps 1 ½ inches. Ex-

perience indicates that particles larger thanthis tend to work themselves to the surfaceover a period of time under traffic. Somewhatmore fine soil is desirable in a mixture that isto serve as a surface, as comp ared with on e fora base. This allow s the su rface to be m oreresistant to the abrasive effects of traffic and

penetration of precipitation. To some extent,moistu re lost by evaporation can be replacedby capillarity.

Emergency airfields that have surfaces of this type require a mixture with a PI between5 and 10. Experience ind icates that r oad sur-

faces of this type shou ld be between 4 and 9.The surface should be made as tight as pos-sible, and good surface drainage should beprovided. For best results, the PI of a stabi-lized soil that is to function first as a wearingsurface and then as a base, with a bituminoussurface being provided at a later date, shouldbe held w ithin very n arrow lim its. Con-sideration relative to comp action, bearingvalue, and frost action are as imp ortant forsurfaces of this type as for bases.

Proportioning

Mixtures of this type are difficult to designand build satisfactorily without laboratorycontrol. A rough estim ate of the p roperproportions of available soils in the field ispossible and d epends on man ual and visualinspection. For example, suppose that a loosesand is the existing su bgrad e soil and it isdesired to ad d silty clay from a n earby borrowsource to achieve a stab ilized m ixture. Eachsoil should be moistened to the point where itis moist, but not w et; in a w et soil, the mois-ture can be seen as a shiny film on the surface,What is desired is a mixture that feels gritty

and in wh ich the sand grains can be seen.Also, w hen the soils are combined in theproper proportion, a cast formed by squeezingthe moist soil mixture in th e hand will not beeither too strong or too weak; it should just beable to withstand normal hand ling w ithoutbreaking. Several trial mixtures shou ld bemade until this consistency is obtained. Theprop ortion of each of the tw o soils should becarefully noted. If gravel is available, thismay be ad ded , although there is no real rule of thum b to tell how mu ch should be add ed. It isbetter to have too much gravel than too little.

Use of Local Materials. The essence of mechanical soil stabilization is the use of lo-cally available materials. Desirable requ ire-ments for bases and surfaces of this type weregiven previously. It is possible, especiallyunder emergency conditions, that mixtures of




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local materials will give satisfactory service,even though they d o not meet the stated re-quirements. Many stabilized mixtures havebeen m ade using shell, coral, soft limestone,cinders, marl, and other materials listed ear-lier. Reliance must be p laced on—

Experience.

An understanding of soil action.The qualities that are d esired in thefinished product.Oth er factors of local imp ortan ce inproportioning such mixtures in thefield.

Blending. It is assum ed in this discussionthat an existing subgrad e soil is to be stabi-lized by ad d ing a suitable borrow soil toproduce a base course mixture that meets thespecified requ irem ents. The m echan ical

analysis and limits of the existing soil willusually be available for the results of the sub-grad e soil sur vey (see Chapter 3). Similarinformation is necessary concerning the bor-row soil. The p roblem is to determine theprop ortions of these two m aterials thatshould be used to produce a satisfactory mix-ture. In some cases, more than two soils mustbe blend ed to produ ce a suitable mixture.However, this situation is to be avoided whenpossible because of the difficulties frequentlyencountered in getting a uniform blend of more than two local ma terials. Trial com-

binations are usually made on the basis of themechan ical analysis of the soil concerned . Inother w ords, calculations are mad e to d eter-mine the gradation of the combined materialsand the proportion of each component ad -justed so that the gradation of thecombination falls within specified limits. ThePI of the selected combination is then deter-mined and comp ared w ith the specification.If this valu e is satisfactory, then the blendmay be assumed to be satisfactory, providedthat the d esired bearing value is attained. If the plasticity characteristics of the first comb-ination are n ot w ithin the sp ecified limits,add itional trials must be mad e. The propor-tions finally selected then may be used in thefield construction process.

Numerical Proportioning. The process of proportioning will now be illustrated by a

numerical example (see Table 9-1, page 9-6).Two materials are available, material B in theroadbed an d material A from a nearby borrowsource. The mechanical analysis of each of these materials is given, together with the LLand PI of each. The desired grading of thecombination is also shown , together w ith the

desired plasticity characteristics.

Specified Gradation. Proportioning of trial combinations may be done arithmetical-ly or graphically. The first step in usingeither the graphical or arithmetical method isto d etermine the gradation requirements.Gradation requirements for base course, sub-course, and select m aterial are found inTables 7-1 and 7-3, TM 5-330/AFM 86-3,V olume II. In the exam p les in Figures 9-1and 9-2, page 9-7, abase course material witha maximum aggregate size of 1 inch has beenspecified. In the grap hical method , thegradation requirements are plotted to theoutside of the right axis. In the arithmeticalmethod , they are p lotted in the columnlabelled “Specs.” Then the gradations of thesoils to be blended are recorded. The graph i-cal method has the limitation of only beingcapable of blending two soils, whereas thearithmetical method can be expan ded toblend as many soils as required. At this point,the prop ortioning method s are distinctiveenough to require separate d iscussion.

Graphical Proportioning. The actualgrad ations of soil m aterials A and B areplotted along the left and right axes of thegraph, respectively. As shown in Figure 9-1,page 9-7, material A has 92 percent passingthe 3/ 4-inch sieve while material B has 72percent passing the same sieve. Once plotted,a line is drawn across the graph, connectingthe percent passing of material A with thepercent passing of material B for each sievesize.

NO TE: Since both m aterials A and B had100 p ercent p assin g the l-inch sieve , itwas omitted from the graph and willn ot affect the resu lts.

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the line for each sieve size. In Figure 9-1, theallowable percent passing the Number 4 sieveranges from 35 to 65 percent passing. Thepoint along the Number 4 line at which 65percent passing intersects represents 82 per-cent material A and 18 percent material B.The 35 percent passing intersects the N um -ber 4 line at 19 percent material A and 81percent m aterial B. The acceptable ranges of material A to be blended with material B isthe w idest range that meets the gradation re-quirements for all sieve sizes. The shaded

area of the chart rep resents the combinationsof the two materials that will meet thespecified gradation requirements. Theboundary on the left represents the combina-tion of 44 percent material A an d 56 percentmaterial B. The position of this line is fixedby the upper limit of the requirement relatingto the material passing the Number 200 sieve(15 percent). The boun dary on the right rep-resents the combination of 21 percentmaterial A and 79 percent material B. Thisline is established by the lower limit of the re-

quirement relative to the fraction p assing theNumber 40 sieve (15 percent). Any mixturefalling within these limits satisfies the grada-tion requirements. For purposes of illustration, assum e that a combination of 30percent material A and 70 percent material

B is selected for a trial mixture, A similardiagram can be p repared for any two soils.

Arithmetical Proportioning. Record th eactual gradation of soils A and B in theirrespective column s (Column s 1 and 2, Figure9-2). Average the gradation limits and recordin the column labelled "S". For example, theallowable range for p ercent passing a 3/ 8-inchsieve in a 1-inch minus base course is 50 to 80percent. The average, 50±80/ 2, is 65 percen t.As shown in Figure 9-2, S for 3/ 8 inch is 65.

Next, determine the absolute value of S-Aand S-B for each sieve size and record in thecolumns labelled “ (S-A)“ and “ (S-B), res-pectively. Sum colum ns (S-A) and ( S-B).To determine th e percent of soil A in the finalmix, use the formu la—

In the example in Figure 9-2:

103 103134 + 103

x 100% = 43.5%=2 3 7

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The percent of soil B in the final mix can bedetermined by the formula:

or

100% - %A = %B

NOTE: If three or more soils are to beblended, the formula w ould b e—

%C =

This formula can be further expanded asnecessary.

Multiply the percent passing each sieve forsoil A by the p ercentage of soil A in th e finalmix; record th e information in column 4 (seeFigure 9-2, page 9-7),Repeat the p rocedu refor soil B and record the information incolum n 5 (see Figure 9-2, page 9- 7). Completethe arithmetical procedure by addingcolumns 4 and 5 to obtain the percent passingeach sieve in the blended soil.

Both the graphical and arithmeticalmethods have advantages and disad-

vantages. The grap hical method eliminatesthe need for precise blending under field con-ditions and the methodology requires lesseffort to use, Its drawback becomes very com-plex when blending more than two soils. Thearithmetical method allows for more preciseblending, such as mixing at a batch plant, andit can be read ily expand ed to accomm odatethe blend ing of three or more soils. It has thedrawback in that precise blending is often un-attainable under field conditions. Thisreduces the quality assurance of the perfor-mance of the blended soil material.

Plasticity Requirements. A method of determining the PI and LL of the combinedsoils serves as a m ethod to ind icate if theproposed trial mixture is satisfactory, pend-ing the p erformance of laboratory tests. Thismay be done either arithmetically or graphi-cally. A grap hical method of obtaining th ese


app roximate values is shown in Figure 9-3.The values shown in Figure 9-3 require add i-tional explanation, a s follows. Consider 500pounds of the mixture tentatively selected (30percent as m aterial A and 70 percent asmaterial B). Of this 500 pou nd s, 150 pou nd sare material A and 350 pound s material B.

Within the 150 pou nd s of material A, thereare 150 (0.52) = 78 pounds of material passingthe N um ber 40 sieve. Within the 350 poun dsof material B, there are 150 (0.05) = 17.5pounds of material passing the N um ber 40sieve. The total amoun t of material passingthe N um ber 40 sieve in the 500 pou nd s of blend = 78+ 17.5= 95.5 pounds, The percent-age of this material that has a PI of 9(material A) is (78/ 95.5) 100= 82. As shown inFigure 9-3, the app roximate PI of the mixtureof 30 percent material A and 70 percentmaterial B is 7.4 percent. By similar reason-

ing, the ap proximate LL of the blend is 28,4percent. These values are somewhat higherthan perm issible und er the specification. Anincrease in the amount of material B willsomewhat reduce the PI and LL of the com-bination.

Field Proportioning. In the field, thematerials used in a mechanically stabilizedsoil mixture probably will be proportioned byloose volume. Assume that a mixture incor-porates 75 percent of the existing subgrad esoil, while 25 percent will be brought in from

a nearby borrow source. The goal is to con-struct a layer that has a compacted thicknessof 6 inches. It is estimated that a loose thick-ness of 8 inches will be required to form the6-inch compacted layer. A more exactrelationship can be established in the field asconstruction p roceeds, Of th e 8 inches loosethickness, 75 percent (or 0.75(8) = 6 inches)will be the existing soil, The remainder of themix will be mixed thoroughly to a depth of 8 inches and compacted by rolling. Theproportions may be more accurately control-led by w eight, if weight measurem ents can be

made under existing conditions.

WaterproofingThe ability of an airfield or road to susta in

operations depends on the bearing strength of the soil. Although an unsurfaced facility maypossess the required strength when initiallyconstructed, exposure to water can result i n a



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loss of strength due to the detrimental effectof traffic operations. Fine-grained soils orgranular materials that contain an excessiveamoun t of fines generally are more sensitiveto w ater changes than coarse-grained soils.Sur face w ater also may contribute to thedevelopment of du st by eroding or loosening

material from the ground surface that can be-come dust during dry weather conditions.

Sources of W ater. Water may enter a soileither by the percolation of p recipitation orponded surface water, by capillary action of un derlying grou nd water, by a rise in thewater-table level, or by condensation of watervapor and accum ulation of moisture un der avapor-impermeable surface. As a generalrule, an existing groundwater table at shal-low depths creates a low load-bearingstrength and mu st be avoided wh erever pos-sible. Methods to protect against moistureingress from sources other than th e groundsurface will not be considered here. In mostinstances, the p roblem of surface water can belessened considerably by following the prop erprocedures for—

Grading.

Compaction.Drainage.

Objectives of Waterproofers. The objec-tive of a soil-surface waterp roofer is to protecta soil against attack by w ater and thuspreserve its in-place or as-constructed

strength during wet-weather operations.The use of soil waterproofers generally islimited to tr affic areas. In some instances,soil waterproofers may be used to prevent ex-cessive softening of areas, such as shou ldersor overruns, normally considered nontrafficor limited traffic areas.

Also, soil waterp roofers may p revent soilerosion resulting from surface water runoff.As in the case of du st palliative, a th in orshallow-depth soil w aterproofing treatment

loses its effectiveness when damaged by ex-cessive rutting and thus can be usedefficiently only in areas that are initially firm.Many soil waterproofers also function well asdust palliatives; therefore, a single materialmight be considered as a treatment in areaswhere the climate results in both wet and drysoil surface conditions. Geotextiles are the




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primary means of waterproofing soils w hengrading, compaction, and drainage practicesare insufficient. Use of geotextiles is d is-cussed in detail in Chapter 11.

CHEMICAL ADMIXTURE STABILIZATION

Chemical admixtures are often used to sta-bilize soils when mechanical methods of stabilization are inadequ ate and r eplacing anun desirable soil with a d esirable soil is notpossible or is too costly. Over 90 percent of allchemical adm ixtur e stabilization p rojectsuse—

Cement.Lime.Fly ash .Bituminous materials.

Other stabilizing chemical admixtures areavailable, but they are not d iscussed in thismanual because they are unlikely to be avail-able in the theater of operations.

WARNING

Chem ical admixtures may contain haz-ardous materials, Consult Appendix C to determine the necessary safetyprecautions for the selected adm ixture.

When selecting a stabilizer additive, thefactors that must be considered are the—

Type of soil to be stabilized.Purpose for which the stabilized layerwill be used.Type of soil quality improvementdesired.Required strength and durability of the stabilized layer.Cost and environmental conditions.

Table 9-2 lists stabilization methods most

suitable for specific applications. To deter-mine the stabilizing agent(s) most su ited to aparticular soil, use the gradation triangle inFigure 9-4, page 9-12, to find the area that cor-responds to the gravel, sand, and fine contentof the soil. For example, soil D has the follow-ing characteristics:

With 95 percent passing the Nu mbersieve, the PI is 14.With 14 percent passing the Nu mber200 sieve, the LL is 21.

Therefore the soil is 5 percent gra vel, 81percent san d, an d 14 percent fines. Figure9-4, page 9-12, show s this soil in Area 1C.

Table 9-3, page 9-13, shows that thestabilizing agents recommend ed for Area 1Csoils include bituminous material, portlandcement, lime, and lime-cement-fly ash. Inthis example, bituminous agents cannot beused because of the restriction on PI, but anyof the other agen ts can be u sed if available.

CementCement can be used as an effective stabi-

lizer for a wide range of materials. In general,however, the soil should have a PI less than30. For coarse-grained soils, the p ercentpassing the Nu mber 4 sieve should be greaterthan 45 percent.

If the soil temperatu re is less than 40degrees Fahrenheit and is not expected to in-crease for one mon th, chemical reactions w illnot occur rapidly. The strength gain of the ce-ment-soil mixture will be minimal. If theseenvironm ental cond itions are anticipated ,

the cement may be expected to act as a soilmodifier, and another stabilizer might be con-sidered for use. Soil-cement m ixtures shou ldbe scheduled for construction so th at suffi-cient d urability will be gained to resist anyfreeze-thaw cycles expected.

Portland cement can be u sed either tomodify and improve the quality of the soil orto transform the soil into a cemented m ass,which significantly increases its strength anddurability. The amount of cement additive

depends on whether the soil is to be modifiedor stabilized . The on ly limitation to theamou nt of cement to be used to stabilize ormod ify a soil pertains to the treatmen t of thebase courses to be used in flexible pavem entsystems. When a cement-treated base coursefor Air Force pavem ents is to be surfaced with


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asphaltic concrete, the percent of cement by find the design cement content based on totalweight is limited to 4 percent. samp le weight expressed as—

Modification. The amou nt of cemen t re- A = 100Bcqu ired to imp rove the qu ality of the soilthrough mod ification is d etermined by the where—trial-and-error approach. To reduce the PI of the soil, successive samples of soil-cement A=

mixtures must be p repared at different treat-ment levels and the PI of each m ixturedetermined. B=

The minimum cement content that yieldsthe desired PI is selected, but since it was c =

determined based on the minus 40 fraction of the material, this value mu st be adjusted to

design cement content, percent of

total weight of soil

percent passing Number 40 sieve,expressed as a d ecimal

percent of cemen t required to obtainthe desired PI of minus Nu mber 40material, expressed as a decimal




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If the objective of mod ification is to im-prove the grad ation of granular soil throughthe addition of fines, the analysis should becond ucted on samp les at various treatmentlevels to determine the minimu m acceptable

cement content. To determine the cementcontent to reduce the swell poten tial of fine-grained plastic soils, mold several samp les atvarious cement contents and soak thespecimens along with untreated specimensfor four days. The lowest cement content thateliminates the swell potential or reducesthe sw ell characteristics to the m inimum

becomes the design cement content. The ce-ment content d etermined to accomp lish soilmodification should be checked to see if itprovides an unconfined compressive strengthgreat enough to qualify for a reduced thick-

ness design according to criteria establishedfor soil stabilization (see Tables 9-4 and 9-5,page 9-14).

Cement-modified soil may be used in frostareas also. In addition to the procedures forthe mixture design described above, curedspecim ens shou ld be su bjected to the 12




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freeze-thaw cycles test (omit w ire brush por-tion) or other app licable freeze-thaw pro-

cedures. This shou ld be followed by a frost-susceptibility test, determined after freeze-thaw cycling, and should meet the require-ments set forth for the base course. If cement-modified soil is used as the subgrade, its frostsusceptibility (determined after freeze-thawcycling) should be used as the basis of thepav emen t thickness design if the red ucedsubgrade-strength design method is applied.

Stabilization. The following p rocedu re is

recommended for determining the design ce-men t content for cemen t-stabilized soils:

Step 1. Determine the classificationand gradation of the untreated soil.The soil must meet the gradation re-quirements shown in Table 9-6 beforeit can be used in a reduced thicknessdesign (multilayer design).

Step 2. Select an estimated cementcontent from Table 9-7 using the soil

classification.

Step 3. Using the estimated cementcontent, determine the compactioncurve of the soil-cement mixture.

Step 4. If the estimated cement con-tent from step 2 varies by more than±2 percent f rom the value in Tables9-8 or 9-9, page 9-16, cond uc tadditional compaction tests, varyingthe cement content, until the valuefrom Table 9-8 or 9-9, page 9-16, iswithin 2 percent of that used for themoisture-density test.

NOTE: Figure 9-5, page 9-17 , i s used inconju nction with Table 9-9, page 9-16.The group ind ex is obtained f rom Fig-ure 9-5, page 9-17 and used to enterTable 9-9, page 9-16.

Step 5. Prepar e samples of the soil-cement mixture for unconfined com-pression and durability tests at the drydensity and at the cement contentdetermined in step 4. Also preparesamples at cement contents 2 percentabove and 2 percent below thatdeterm ined in step 4. The sam plesshould be prepared according toTM 5-530 except that when morethan 35 percent of the material isretained on the Number 4 sieve,




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a CBR mold should be used toprepare the specimens. Cure thespecimens for seven days in a hu midroom before testing. Test three spec-imens using the u nconfined com-pression test and subject three spec-imens to durability tests. These testsshould be either wet-dry tests forpavements located in nonfrost areasor freeze-thaw tests for p avem entslocated in frost areas.

Step 6. Comp are the r esults of theunconfined comp ressive strength anddurability tests with the require-men ts shown in Tables 9-4 and 9-5.

The lowest cement content thatmeets the required unconfined com-pressive strength requirementand demonstrates the requireddurability is the design content.If the mixture should meet thedurability requirements but notthe strength requirements, themixture is considered to be amodified soil.

Theater-of-operations construction re-quires that the engineer make maximum useof the locally available constructionmaterials. However, locally availablematerials may not lend themselves to




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classification under the USCS method. Theaverage cement requ irements of comm on lo-cally available constru ction materials isshown in Table 9-10.

Lime

Experience has shown that lime reacts withmed ium -, mod erately fine-, and fine-grainedsoils to produce decreased plasticity, in-creased workability and strength, andreduced swell. Soils classified according tothe USCS as (CH), (CL), (MH), (ML), (SC),(SM), (GC), (GM), (SW-SC), (SP-SC), (SM-SC), (GW-GC), (GP-GC), and (GM-GC)should be considered as potentially capable of being stabilized w ith lime.

If the soil temperature is less than 60degrees Fahrenheit and is not expected to in-

crease for one mon th, chemical reactions w illnot occur rapidly. Thus, the strength gain of the lime-soil mixture will be minimal. If these environmental cond itions are expected,the lime m ay be expected to act as a soilmodifier. A possible alternative stabilizermight be considered for use. Lime-soil mix-tures should be scheduled for construction sothat sufficient durability is gained to resistany freeze-thaw cycles expected.

If heavy vehicles are allowed on the lime-stabilized soil before a 10- to 14-day curingperiod, pavement damage can be expected.Lime gains strength slowly an d requiresabout 14 days in hot weather and 28 days incool weather to gain significant strength . Un-

surfaced lime-stabilized soils abrade rapidlyun d er traffic, so bitum inous su rface treat-ment is recommended to prevent surfacedeterioration.

Lime can be used either to mod ify some of the ph ysical properties and thereby improvethe qu ality of a soil or to transform the soilinto a stabilized mass, which increases itsstrength and durability. The amount of limeadditive depends on whether the soil is to re-modified or stabilized. The lime to be used

ma y be either hyd rated or quicklime, al-though most stabilization is done usinghyd rated lime. The reason is that quicklimeis highly caustic and d angerous to use. Thedesign lime contents determined from thecriteria presented herein are for hydratedlime. As a guide, the lime contents deter-mined h erein for hydrated lime should bereduced by 25 percent to determine a designcontent for quicklime.




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I

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after mixing, the lime-soil mixtureshould be allowed to mellow for notless than one hour n or more than tw ohours; after compaction, each spec-imen should be w rapp ed securely toprevent moisture loss and should be

cured in a constant-temperature cham-ber at 73 degrees Fahrenheit ±2degrees Fahrenheit for 28 days. Pro-cedures for conducting unconfinedcompression tests are similar to thoseused for soil-cement sp ecimen s exceptthat in lieu of m oist cur ing, the lime-soil specimens should remain securelywrapped until testing.

Step 4. Comp are the r esults of theun confined comp ressive tests with the

criteria in Table 9-4, page 9-14. Thedesign lime content must be the low-est lime content of specimens meetingthe strength criteria indicated.

Ot her Additives. Lim e may be used as apreliminary add itive to redu ce the PI or altergradation of a soil before ad ding th e primarystabilizing agent (such as bitum en or ce-men t). If this is the case, then the d esign limecontent is the m inimu m treatment level thatwill achieve the desired resu lts. For nonp las-tic and low-PI materials in which lime alonegenerally is not satisfactory for stabilization,fly ash may be ad ded to prod uce the necessaryreaction.

Fly Ash

Fly ash is a pozzolanic material that con-sists mainly of silicon and aluminumcomp ound s that, wh en mixed w ith lime andwater, forms a hardened cementitious masscapable of obtaining high compressionstrengths. Fly ash is a by-product of coal-

fired, electric power-generation facilities.The liming quality of fly ash is highly depend-ent on the type of coal used in powergeneration. Fly ash is categorized into twobroad classes by its calcium oxide (CaO) con-tent. They are—

Class C.Class F.

Class C. This class of fly ash has a high CaOcontent (12 percent or m ore) and originatesfrom subbituminous and lignite (soft) coal.Fly ash from lignite has the highest CaO con-tent, often exceed ing 30 percent. This typ ecan be used as a stand-alone stabilizing

agent. The strength characteristics of ClassC fly ash having a CaO less than 25 percentcan be improved by adding lime. Further dis-cussion of fly ash p roperties and a listing of geograph ic locations where f ly ash is likely tobe found are in Appendix B.

Class F. This class of fly ash has a low CaOcontent (less than 10 percent) and originatesfrom anthracite and bituminous coal. Class Ffly ash has an insufficient CaO content for thepozzolanic reaction to occur. It is not effective

as a stabilizing agent by itself; however, whenmixed with either lime or lime and cement,the fly ash mixture becomes an effectivestabilizing agen t.

Lime Fly A sh Mixt ures. LF mixtures cancontain either Class C or Class F fly ash. TheLF design process is a four-part process thatrequires laboratory analysis to determine th eoptimum fines content and lime-to-fly-ashratio.

Step 1. Determine the optimum fines

content. This is the percentage of flyash that results in the maximum den-sity of the soil mix. Do th is by con-ducting a series of moisture-densitytests using different p ercentages of fly ash and then d etermining the m ixlevel that yields maximum density.The initial fly ash content should beabout 10 percent based on th e weightof the total mix. Prepare test samplesat increasing increments (2 percent)of fly ash, up to 20 percent. The

design fines content should be 2 per-cent above the optimum fines content.For example, if 14 percent fly ashyields the maximum density, thedesign fines content w ould be 16 per-cent. The m oisture den sity relationwould be based on the 16 percentmixture.


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Step 2. Determine the rates of lime tofly ash, Using the design fines con-tent and the OMC determined in step1, prepare triplicate test samples atLF ratios of 1:3, 1:4, and 1:5. Cure alltest samples in sealed containers for

seven d ays at 100 degrees Fahrenh -e i t .

Step3. Evaluate the test samples forun confined comp ressive strength . If frost is a consid eration , subject a setof test sam ples to 12 cycles of freeze-thaw durability tests (refer to FM5-530 for actual test procedures).

Step 4. Determine the design LFratio. Compare the results of the

unconfined st rength test andfreeze-thaw durability tests with theminimum requirements found inTables 9-4 and 9-5, page 9-14,respectively. The LF ratio with th elowest lim e content th at m eets therequired unconfined compressivestrength and demonstrates therequired durability is the design LFcontent. The treated material must alsomeet frost susceptibility requirementsas ind icated in Special Report 83-27. If the mixture meets the durability

requirements but not the strengthrequirements, it is considered to be amod ified soil. If neither strength nordurability criteria are met, a differentLF content may be selected and thetesting p rocedu re repeated.

Lime-Cement-Fly Ash (LCF) Mixtures.The design method ology for determining theLCF ratio for deliberate construction is thesame as for LF except cement is added in step2 at the ratio of 1 to 2 percent of the design

fines content. Cement may be used in place of or in addition to lime; how ever, the d esignfines content should be maintained.

When expedient construction is required,use an initial mix proportion of 1 percentportland cement, 4 percent lime, 16 per-cent fly ash, and 79 percent soil. Minimum

unconfined strength requirements (seeTable 9-4, page 9-14) must be met. If testspecimens do not meet strength require-ments, add cement in 1/ 2 percent incrementsuntil strength is adequate. In frost-suscep-tible areas, durability requirements must

also be sa tisfied (see Table 9-5, page 9-14).

As with cement-stabilized base coursematerials, LCF mixtures containing morethan 4 percent cement cannot be used as basecourse material under Air Force airfield pave-ments.

Bitumin ous M aterialsTypes of bituminou s-stabilized soils are—

Soil bitumen. A cohesive soil systemmad e water-resistant by ad mixture.

Sand bitum en. A system in whichsand is cemented together by bitum i-nous material.Oiled earth. An earth-road systemmad e resistant to w ater absorptionand abrasion by means of a sprayedapplication of slow- or medium-curingliquid asphalt.Bitumen-waterproofed, mechanicallystabilized soil. A system in which twoor more soil materials are blended toprod uce a good gradation of particles

from coarse to fine. Comparativelysmall amounts of bitumen are needed,and the soil is compacted.Bitumen -lime blend. A system in w hichsmall percentages of lime are blendedwith fine-grained soils to facilitate thepenetration and mixing of bitumensinto the soil.

Soil Gradation. The recommended soilgradations for subgrade materials and baseor subbase course materials are shown inTables 9-11 and 9-12, respectively. Mechani-

cal stabilization may be required to bring soilto proper gradation.

Types of Bitumen. Bituminous stabiliza-tion is generally accomplished using—

Asphalt cement.Cutback asphalt.Asphalt emulsions.




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preferred, first determ ine the general type of aggregate. If the aggregate contains a highcontent of silica, as shown in Figure 9-7 , page9-25, a cationic emulsion should be used (seeFigure 9-8, page 9-25.). If the aggrega te is acarbonate rock (limestone, for examp le), ananionic emulsion should be used.

Figures 9-9 and 9-10 can be used to find themix design for asphalt cement. Thesepreliminary quantities are used for expedientconstruction. The final design content of as-phalt should be selected based on the resultsof the Marsha ll stability test procedu re. Theminimu m Marshall stability recommendedfor subgrad es is 500 pou nd s; for base courses,750 pounds is recommended . If a soil does notshow increased stability w hen reasonableamoun ts of bituminous materials are add ed,the grad ation of the soil should be modified oranother type of bituminous material shouldbe used. Poorly grad ed materials m ay be

improved by adding suitable fines containingconsiderable material passing a Nu mber 200sieve. The amoun t of bitumen requ ired for agiven soil increases with an increase in per-centage of the finer sizes.

Section II. Design Concepts

STRUCTURAL CATEGORIESProcedures are presented for d etermining

design thicknesses for two structuralcategories of pavem ent. They are—

Single-layer.Multilayer.

Typical examp les of these pavements are in-dicated in Figure 9-11.

A typ ical single-layer pavement is a stabi-

lized soil structure on a natural subgrade.The stabilized layer may be mixed in place orpremixed an d later p laced over the existingsubgrad e. A waterproofing surface such asmembrane or a single bituminous surface(SBST) or a double bituminous surface treat-ment (DBST) may also be provided. Amultilayer structure typically consists of atleast two layers, such as a base and a wearingcourse, or three layers, such as a subbase, abase, and a wearing course. A thinwaterproofing course may also be used on

these structures. Single-layer and multi-layer pavement design procedures arepresented for all categories of road s and forcertain categories of airfields as ind icated inTable 9-15, page 9-28.

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Both single-layer and multilayer pavementstructures may be constructed under eitherthe expedient or nonexpedient concept. Dif-ferent structural designs are provid ed toallow the design engineer wider latitude of choice. However, single-layer structures areoften associated w ith exped ient constructionrather than n onexpedient construction, andmu lti layers are nonexpedient and per-man ent. Certain considerations shou ld bestudied to determine whether to use a single-layer or mulilayer design under eitherconcept.

The overall concept of d esign as d escribedherein can be d efined in four basic determina-tions as ind icated in Table 9-16.

STABILIZED PAVEMENTDESIGN PROCEDURE

To use different stabilized m aterials effec-tively in tra nsportation facilities, the d esignprocedure must incorporate the advantagesof the higher qu ality m aterials. These ad -vantages are usually reflected in better

performance of the structures and a reductionin total thicknesses required. From astand poin t of soil stabilization (not m od ifica-tion), recent comparisons of behavior basedon type an d quality of material have shownthat stabilization provides definite structuralbenefits. Design results for airfield and road


classifications are presented to provideguidance to the designer in determiningthickness requirements w hen u sing stabi-lized soil elements. The design thickness alsoprovides the planner the option of comparingthe costs of available types of pavement con-struction, thereby providing the beststructure for the situation.

The design pr ocedu re pr imarily incorporatesthe soil stabilizers to allow a red uction of thickness from the conventional flexible

pavement-design thicknesses. These thick-ness reductions depend on the properconsideration of the following variables:

Load.Tire p ressure.Design life.Soil properties.Soil strength.Stabilizer type.Environmenta l cond itions.Other factors.

The d esign curves for theater-of-operationsairfields and road s are given for single-layerand mu lti layer pavements later in this sec-tion.

In the final analysis, the choice of the ad-mixture to be used depends on the economics



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and availability of the materials involved.The first decision that shou ld be m ad e iswhether stabilization should be attemptedat all. In some cases, it may be economicalmerely to increase the compaction require-ments or, as a minimum, to resort toincreased p avem ent th ickness. If locallyavailable borderline or unacceptablematerials are encountered, definite con-sideration should be given to upgrad ing anotherw ise unacceptable soil by stabilization.

The rapid method of mix design should beindicative of the type and percentage of stabi-lizer required and the required designthickness. This procedu re is meant to be afirst-step type of approach and is by no meansconclusive. Better 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 9-17. Evenwhen stabilized materials are used, proper

construction techniques and control practicesare mandatory.

THICKNESS DESIGN PROCEDURES

The first p aragrap hs of this section g ivethe design engineer information concerningsoil stabilization for construction of theater-of-operations roads and airfields. The

information includes procedures for deter-mining soil’s suitability for stabilization anda means of determining the approp riate typeand amount of stabilizer to be used. The finalobjective in th is total systematic approach isto determine the required design thicknesses.Depending on the type of facility and the AI orthe CBR of the u nstabilized subgrad e, thedesign procedure presented in this section al-lows determ ination of the required th icknessof an overlying stru cture that mu st be con-structed for each anticipated facility.

This basic structural design problem mayhave certain conventional overr iding factors,




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such as frost action, that influence this re-quired thickness. The d ecision to stabilize ornot may be based on factors other than struc-tur al factors, such as economy, availability of stabilizer, and time. It must be realized thatsoil stabilization is not a cure for all militaryengineering problems. Proper use of thismanual as a guide allows, in some cases,reductions in required thicknesses. Theprim ary benefit in soil stabilization is tha t itcan provide a means of accomplishing orfacilitating construction in situations inwhich environmental factors or lack of suitable materials could preclude or seriouslyhamper work progress. Through the properuse of stabilization, marginal soils can oftenbe transformed into acceptable constructionmaterials. In m any instances, the qu antity of materials required can be redu ced andeconom ic ad vantag es gained if the cost of

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

The stru ctural benefits of soil stabilization,show n by increased load-carrying capab ility,are generally known. In addition, increasedstrength and du rability also occur w ithstabilization.

Generally, lesser am oun ts of stabilizersm ay be used for increasing the d egree of workability of a soil without effectively in-creasing structural characteristics. Also,greater percentages may be used for increas-ing strength at the risk of being uneconomicalor less du rable. Som e of the inform ationpresented is intend ed for use as guid ance onlyand should not supersede specific trial-proven m ethods or laboratory testing w heneither exists.

Primary considerations in determiningthickness design are those that involve thedecision to construct a single-layer or m ulti-layer facility, as discussed earlier. Themethod chosen depend s on the type of con-struction. All permanent construction and

m ost mu lti layer d esigns shou ld use thereduced thickness design procedure. Usuallythe single layer is of expedient d esign.

ROADS

Specific procedures for d etermining totaland/ or layer thicknesses for roads are dis-


cussed below. The more expedient m ethodsare shown first, followed by more elaborateprocedures. Road classification is based onequivalent nu mber 18-kip, single-axle, dual-wheel applications. Table 9-18 lists theclasses of roads.

Single-Layer

For each category of roads (Classes Athrough E), a single design curve is presentedthat applies to all types of stabilization (seeFigures 9-12 through 9-14 and Figure 9-16,page 9-32). These curves indicate the totalpavement thickness required on an unstabil-ized subgrade over a range of subgradestrength values. It should be noted that eachcurve terminates above a certain subgrade

CBR. This is because design strength criteriafor u nsurfaced road s indicate that a n aturalsoil of this appropriate strength could sustainthe traffic volume required of this category of facility without chemical stabilization. Thefollowing flow d iagram ind icates the use of these design procedures:



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Redu ced thickness design factors, (see-Table 9-20 and Figure 9-20, page 9-36 ) shouldbe applied to conventional design thicknesswhen designing for permanent and nonex-ped ient road and airfield design. The use of stabilized soil layers within a flexible pave-ment pr ovides the opp ortunity to reduce theoverall thickness of pavement structure re-quired to sup port a given load. To design apavement containing stabilized soil layers re-

quires th e application of equ ivalency factorsto a layer or layers of a conventionallydesigned pavement. To qualify for applicationof equivalency factors, the stabilized layermust meet appropriate strength anddu rability requirements set forth in TM 5-822-4/AFM 88-7, Chapter 4. An equivalen-cy factor represents the number of inches of aconventional base or subbase that can bereplaced by 1 inch of stabilized material.Equivalency factors are d etermined from—

Table 9-20 for bitum inous stabilizedmaterials.

Figure 9-20, page 9-36, for materialsstabilized with cement, lime, or acombination of fly ash m ixed w ithcement or lime.

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

equivalency factor from Figure 9-20, page9-36, requires that the u nconfined compres-sive strength, determined according to ASTMD1633, is known. Equivalency factors aredetermined from Figure 9-20, page 9-36, forsubbase materials only. The relationship es-tablished between abase and a subbase is 2:1.Therefore, to determine an equivalency factorfor a stabilized base course, divide the sub-base factor from Figure 9-20, page 9-36, by 2.

See TM 5-330/AFM 86-3, Volume II for con-ventional design procedures.


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AIRFIELDSSpecific pr ocedures for d etermining th e

total and/ or layer thicknesses for airfields arediscussed in the following paragraphs. Themore expedient m ethods are shown first, fol-lowed by more elaborate procedures.

Airfields are categorized by th eir position onthe battlefield, the runway length, and thecontrolling aircraft. Table 9-21 lists aircraftcategories.

Single-LayerDesign curves for single-layer airfield con-

struction are in Figures 9-21 through 9-28,pages 9-38 through 9-44. In these figures

the controlling a ircraft and d esign life incycles (one cycle is one takeoff and one land-ing) are indicated for each airfield cate-gory. The design curves are ap plicable for alltypes of stabilization over a range of subgradestrengths up to a maximu m above w hich

stabilization wou ld generally be un w ar-ranted if the indicated material subgradestrength could be maintained. Design curvesare p resented for typical theater-of-opera-tions gross w eights for the controlling aircraftcategory. For a single-layer facility, a th inwearing course may p rovide waterproofing orminimize abrasion resulting from aircrafttires. The following flow d iagram ind icatesthese procedures:




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Multilayer

In the design of multilayer airfields, it isfirst necessary to determine the total designthickness based on conventional flexiblepavement criteria. Then an approp riatereduction factor is applied for the particularsoil-stabilizer combination anticipated foruse. Determinations of individual layer

thickness finalizes the design. Conventional

flexible pavement design curves and proce-du res may be found in TM 5-330/AFM 86-3,V olume II. After total thickness has beendetermined, a reduction factor is applied (seeTable 9-22 or 9-23, page 9-45). Individuallayer thicknesses can be determined usingTable 9-24, page 9-46,and procedures indi-cated for mu lti layer road s. The following flow

diagram indicates these design procedures:




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EXAMPLES OF DESIGN

Use of the d esign criteria in this section canbest be illustrated by examples of typicaldesign situations.

Example 1

The mission is to construct an airfield forthe logistical supp ort of an infantry d ivision

and certain non division artillery units. Thefacility must sustain approximately 210takeoffs and landings of C-130 aircraft,operating at 150,000 pounds gross weight,along w ith op erations of smaller aircraft. Be-cause of unsatisfactory soil strengthrequ irements an d availability of chemicalstabilizing agents, stabilization is to be con-sidered. The facility is also considered anexpedient single-layer design.

A site reconnaissance and a few soil

samp les at the proposed site ind icate the fol-lowing:

The natural strength is 8 CBR.It has a PI of 15.It has a LL of 30.Twenty percent passes a Number 200sleve.

Thirty percent is retained on a Num-ber 4 sieve.

The classification is (SC).

Using th is information, a determinationcan be made from Figure 9-4, page 9-12, andTable 9-3, page 9-13, that the prop er agent iscement, lime, or fly ash. The soil-lime pH testindicates that a lime content of 3 percent is re-qu ired to p roduce a p H of 12.4. Since the soilclassified as an (SC), an est imated cementcontent o f 7 percent is selected from Table9-7, page 9-15. The fly ash ratio is 4 percentlime, 1 percent cement, 16 percent fly ash,and 79 percent soil. The characteristics of alladd itives are then reviewed, and because of predicted cool weather conditions, cementstabilization is chosen.

The design thickness is then d etermined.The facility w ill be designed as a close battle

area 3,000’ airfield designed for 420 cycles of aC-130 aircraft. To determine the designthickness. Figure 9-1, page 9-7, is used . For asubgrade strength of 8 CBR and interpolatingbetween the 125,000- and 175,000-pound cur-ves, the required design thickness is 13 1/ 2inches.




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Examp le 2

The mission is to p rovid e a rear ar ea 6)000’airfield facility for C-5A aircraft op erating at

320,000 pou nd s gross w eight. Time an dmaterials indicate that a multilayer facilitycan be constructed using nonexpedientmeth ods. A site reconnaissance ind icates thefollowing:

The natural strength is 5 CBR.It has a PI of 5.It has a LL of 35.Fifteen percent p asses the N u m ber200 sieve.Sixty percent is retained on the Num-ber 4 sieve.

The classification is (GM).

Chemical stabilization is considered for theup per su bgrad e, but a sup ply of 100-CBRbase course material is available. An asp hal-tic concrete wearing course w ill be used .Since the soil classified as (GM), either

bituminous, fly ash, or cement stabilization isappropriate (see Figure 9-4, page 9-12, an dTable 9-3, page 9-13).Because of the lack of

adequate quantities of cement and fly ash,bitum inous stabilization will be tried.

The material is termed “sand-gravelbitum en. ” Table 9-13, page 9-24, recom-mend s either asph alt cutbacks or emu lsions(considerable materials p assing the N um ber200 sieve); since cutback asphalt is available,it will be used. It is anticipated that the in-place temperatu re of the sand will be abou t100 degrees Fahrenheit. (From Table 9-13,page 9-24, it can then be determined that thegrade of cutback to be used is MC-800. Fromthe equation given on page 9-23 and thegradation curve (not shown for the example),a p reliminary design content of 6.7 percentasph alt is determined .) Design sp ecimensare then molded and tested u sing the proce-du res indicated in TM 5-530. Comparing thetest results with the criteria given p reviously




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18-kip equ ivalent loads and a CBR of 50; a 4-inch asphaltic cement pavement and a10-inch cement -stabilized base a re requ ired.

Examp le 5The mission is to provide an expedient tac-

tical support ar ea airfield for the operation of approximately 7,000 cycles of F-4C traffic.The single-layer design is selected. A sitereconnaissance reveals the following :

The natu ral strength is 4 CBR.It has a PI of 12.Eleven percent passes a N um ber 200sieve.Twenty percent retained on a Num-ber 4 sieve.Organic material occurs as a trace inthe soil samp les.

Climatological data ind icate a trend forsubfreezing weather, and full traffic must beapplied immediately upon completion. Or-dinar ily, based on information from Figure9-4, page 9-12, and Table 9-3, page 9-13,either cement, lime, or fly ash stabilizationwou ld be the app ropriate agent for this situa-tion and the soil wou ld classify as an (SW-SM)bord erline. With the constraints on curingtimes, soil stabilization wou ld not be the ap-propriate method of construction. Another

means, possibly landing mats, must be con-sidered for the successful comp letion of themission.

Example 6The mission is to provide an expedient

Class E road between two organizational taskforces. The single-layer design is selected.The preliminary site investigation for a por-tion of the road indicates a natural soilstrength of 30 CBR. The design curve for thisroad classification, shows that a 30-CBR soilis adequate for the intended traffic and that it

does not requ ire any stabilization (see Figure9-15, page 9-32). Therefore, no soil samplingor testing is necessary. A problem area maylater arise from a reduction of strength, thatis, a large volum e of rainfall or a dust p roblemon this particular road.

THEATER-OF-OPERATIONS AIRFIELDCONSIDERATIONS

In the theater of operations, the lack of trained p ersonnel, specialized equ ipment, ortime often eliminates consideration of manylaboratory p rocedures. The CBR and special

stabilization tests in p articular w ill not beconsidered for these reasons. As a result,other methods for d etermining d esign p ave-men t thicknesses have been developed usingthe AI (see TM 5-330/AFM 86-3, Volume II).This system is purely expedient and shouldnot replace laboratory testing and reducedthickness design procedures.

Functions of Soil StabilizationAs previously discussed, the three primary

functions of stabilization are—

Strength imp rovement.Dust control.Waterproofing.

Use of Table 9-25 allows the engineer toevaluate th e soil stabilization fun ctions asthey relate to different types of theater-of-operation s airfields. It is possible to easilysee the uses of stabilization for the traffic ornontraffic areas of airfields. This table,developed from Table 9-26, page 9-50, showsthe p ossible functional consid erations for

situations wh ere either no landing m at, alight-duty mat, or a medium -duty mat may beemployed. (Landing mats are discussed inTM 5-330/AFM 86-3, Volume II and TM 5-33 7.) As an example of the use of this table,consider the construction of the “heavy lift inthe support area.”

Referring to the traffic areas, a certain min-imum strength is required for unsurfaced-soiloperations (that is, without a land ing mat) orif either the light duty mat (LM) or themed ium du ty mat (MM) is used. If the exist-ing soil strength is not adequate, stabilizationfor strength improvement may be consideredeither to sustain unsurfaced operations or tobe a necessary base for the land ing ma t. Fur-ther, if no m at is used , stabilization might beneeded only to provide dust control and/ or soil




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waterproofing. If a landing mat is used, how-ever, the functions of dust control and soilwaterproofing would be satisfied andstabilization need not be considered in anyevent. Possible stabilization functions fornontraffic areas have been shown in a similarmanner. For certain airfields, such as the“light lift in the batt le area, ” no function forstrength improvement in either traffic or non-traffic areas is ind icated . Such airfields h avean AI requirement of 5 or more unsurfacedoperations (see Table 9-26, page 9-50). Siteselection should be exercised in most in-stances to avoid areas of less than a 5 AI. Forcertain airfields, such as the “tactical in thesupport area,“ a landing mater improved sur-facing always will be provided. Therefore a“no m at” situation p ertains only to the non-traffic areas.

Design Requirementsfor Strength Improvement

Where stabilization for strength improve-ment is considered, certain basic designrequirem ents, in terms of strength and thick-ness of a stabilized soil layer on a givensubgrade, mu st be met. The strength andthickness requirements vary depending onthe operational traffic parameters andthe strength of the soil d irectly beneath thestabilized soil layer. Since the traffic

param eters are known for each airfield type,a minimu m strength requirement for the sta-bilized soil layer can be sp ecified for eachairfield based on u nsu rfaced-soil criteria. Forany given subgrade condition, the thicknessof a minimum-strength, stabilized-soil layernecessary to prevent overstress of the sub-grade also can be d etermined. Table 9-27 ,page 9-52, gives design requirem ents for traf-fic and nontraffic areas of different airfieldtypes for wh ich stabilization may be used forstrength imp rovement. As seen, the mini-mum-strength requirement in terms of AI is a

function only of the app lied traffic for a par-ticular airfield an d is ind epend ent of thesubgrade strength . How ever, the thickness isa direct function of the underlying subgradestrength.

Proper evaluation of the subg-rade is essen-tial for establishing thickness requirements.

In evaluating th e subgrade for stabilizationpurposes, a representative AI strength profilemu st be established to a dep th that w ouldpreclude the possibility of overstress in th eunderlying subgrade. This depth variesdepending on the—

Airfield.Pattern of the p rofile itself.Manner of stabilization.

In this regard, the thickness data given inTable 9-27, page 9-52, can be used also to pro-vide guidance in establishing an adequatestreng th p rofile. Generally, a p rofile to adepth of 24 inches is sufficient to ind icate thestrength profile pattern. However, if adecrease in strength is suspected in greaterdepths, the strength profile should be ob-tained to no less than th e thickness ind icatedin Table 9-27, page 9-52,un der the 5-6 sub-grade AI colum n for the ap prop riate airfield.

The use of Table 9-27, page 9-52, to estab-lish the design requirements for soilstabilization is best illustrated by the follow-ing example: Assume that a rear area 3,500’airfield is to be constructed and that a sub-grade AI evaluation h as been mad e fromwh ich a represen tative profile to a sufficientdepth can be established. One of threegeneral design cases can be considered de-

pend ing on the shape of the strength p rofile.

The first case considers constantstrength with depth; therefore, the re-quired thickness is read directly fromTable 9-27 , page 9-52, und er the ap-propriate subgrad e AI column. Thus,in the example, if a subgrade AI of 8is measured, the required thickness of a stabilized soil layer if no land ingmat w ere used w ould be 18 inches.The required minimum strength of

this stabilized soil layer is an A I of 15. If the light landing mat wereused, a 6-inch-thick layer with a min-imum AI of 10 wou ld be required as abase overlying the subgrade AI of 8.The second case considers an increasein strength w ith dep th; therefore, therequired thickness of stabilization

Soil Stabilization for Roads an d Airfield s 9-51



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Soil Stabilization for Road s and Airfields 9-52



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ma y be considerably less than indi-cated in th e table. For th is example,assum e that th e AI increases w ithdepth as shown in Figure 9-29. A sta-bilized layer can be prov ided either bybuilding up a compacted base cm top

of the existing grou nd surface or bytreat ing th e in-place soil. Because of this, each situation represents asomewhat different design problem.

An in-place treatm ent is analogous toreplacing the existing soil to some depth withan improved quality material. Wherestrength increases with depth, the point atwhich thickness is compatible with thestrength at that par ticular point m ust bedetermined. This point can be determined

graphically simply by superimposing a plot of the thickness design requ irements versussubgrad e AI (see Table 9-27) directly on thestrength profile plot. This procedure isshown in Figure 9-29. The depth at w hich thetwo plots intersect is the d esign thickness re-quirement for a stabilized-soil layer. In theexample, a thickness of 9.5 inches (or say 10inches) is required .

If a comp acted base of a select borrow soil isused to provide a stronger layer on the sub-grade shown in Figure 9-29, the thicknessmu st again be consistent with the strength atsome depth below the surface of the placedbase-cou rse layer. Since the base-courselayer itself will be constructed to a minimumAI of 15, the weakest p oint un der th e placedbase w ill be at th e su rface of the existingground , or in this instance an AI of 8. Usingthis value, Table 9-27 gives a thickness of 18inches of base course. Compaction of the ex-isting ground would be beneficial in term s of thickness requirements if it w ould increasethe critical subgrade strength to a higher

value. If, for example, the minimum AI of theexisting groun d could be increased from 8 to12, the thickness of base required would bereduced to 10 inches (see Table 9-27 ).

The third case considers a d ecrease instrength with depth. The strengthprofile show n in Figure 9-30, page9-54 indicates a crust of firm material

over a significantly weaker zone of soil beneath. In this example, the impor-tance of proper analysis of subgradeconditions is stressed. If strength d atawere obtained to less than 30 inches,the adequacy of the design could notbe fully determined.

Consider again a n in-place stabilizationprocess. Although the strength profile and

design curve intersect initially at a shallowdepth (about 3 inches) (see Figure 9-30, page9-54), the strength p rofile does not remain tothe right of the design curve. This ind icatesthat the d esign requ irement has been satis-fied. The second and final intersection occursat 24 inches. Since there is no indication of afurther decrease in strength w ith dep th, athickness of 24 inches is therefore requ ired.

In the case of a compacted base placed on asubgrade that decreases in strength withdep th, the procedu re for determining thedesign thickness is more difficult. The designthickness can be determined by comparingthe strength-depth profile with the designcurve. If the measu red AI at any given dep this less than the minimum requirement shownby the design curve, a su fficient thickness of improved quality soil must be placed on theexisting ground su rface to prevent overstress




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at that d epth . However , the thickness of base

necessary mu st be such that the requ ire-men ts will be met at all depth s. To satisfythis condition, the required thickness must beequal to the maximum difference, which willoccur at a p articular strength va lue, betweenthe dep th indicated by th e design curve andthe depth from the strength-dep th profile, Inthe example shown in Figure 9-30, this max-imum difference occurs at an AI of 12. Thedifference is 10 inches, which is the requ iredthickness for an impr oved qu ality base.

The sam e procedu res described for adecrease in strength with d epth can be usedto derive the strength an d thickness require-ments for a base course under either an LM orMM. The thickness design requ irementsgiven herein are for stabilized soil layershaving a minimum strength property to meetthe particular airfield traffic need. Although

the strength actually achieved may well ex-ceed the minimum requirement, noconsideration should be given to reducing thedesign thickness as given in Table 9-27 , page9-52, or as developed by the stated proce-dures.

Section III. Dust Control

EFFECTS O F DUSTDust can be a major p roblem d uring combat

(and training) operations. Dust negativelyimpacts morale, maintenance, and safety.Experience during Operation DesertShield/ Storm su ggests that du st was a majorcontributor to vehicle accidents. It also ac-celerated w ear and tear on veh icles andaircraft components.

Dust is simp ly airborne soil particles. As ageneral rule, dust consists p redominantly of soil that has a particle size finer than 0.074mm (that is, passing a Number 200 sieve).

The presence of dust can have significantad verse effects on the overa ll efficiency of aircraft by—

Increasing d own time an d mainte-nance requirements.Shortening engine life.Reducing visibility.

Affecting the h ealth a nd m orale of personnel.

In add ition, dust clouds can aid the enemy byrevealing p ositions and th e scope of opera-tions.

DUST FORMATION

The presence of a relative amount of dust-size particles in a soil surface does notnecessarily ind icate a du st problem nor theseverity of dust that w ill result in various

situations. Several factors contribu te to thegeneration, severity, and p erpetuity of du stfrom a poten tial grou nd source. These in-clude—

Overall gradation.Moisture content.Density and smoothness of theground surface.




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Presence of salts or organic matter,vegetation, and wind velocity anddirection.Air humidity.

When conditions of soil and environment

are favorable, the position of an external forceto a ground surface generates dust that existsin the form of clouds of various density, size,and height above the ground. In the case of aircraft, dust may be generated as a result of erosion by propeller wash, engine exhaustblast, jet-blast imp ingement , and th e draft of moving aircraft. Further, the kneading andabrading action of tires can loosen particlesfrom the ground surface that may become air-borne.

On unsurfaced roads, the source of dust

may be the roadway surface. Vehicle trafficbreaks down soil structure or abrades gravelbase courses, creating fine-grained particlesthat readily become airborne when trafficked.

DUST PALLIATIVESThe primary objective of a dust palliative is

to p revent soil particles from becoming air-borne. Dust palliative may be required forcontrol of dust on nontraffic or traffic areas orboth. If a prefabricated landing mat,membrane, or conventional pavement surfac-ing is used in the tr affic areas of an airfield,

the use of dust p alliative wou ld be limited tonontraffic areas. For nontraffic areas, a pal-liative is needed that can resist the maximumintensity of air blast im pingem ent by anaircraft or the prevailing winds. Where dustpa lliative p rovide the n ecessary resistanceagainst air impingem ent, they may be totallyunsuitable as wearing surfaces. An impor-tant factor limiting the app licability of a du stpalliative in traffic areas is the extent of su r-face ru tting th at w ill occur un der traffic. lf the bearing capacity allows the soil surface torut under traffic, the effectiveness of a shal-low-depth palliative treatment could bedestroyed rapidly by breakup and subsequentstripp ing from the ground surface. Some pa l-liatives tolerate deformations better thanothers, but n orm ally ru ts 1½ inches d eepresult in the virtual destruction of any thinlayer or shallow d epth p enetration d ust pal-liative treatment.

The success of a dust-control programdep end s on the engineer’s ability to match adust palliative to a specific set of factors af-fecting dust generation. These factorsinclude—

Intensity of area use.

Topography.Soil type.Soil surface features.Climate.

Intensity of Area UseAreas requiring dust-control treatments

shou ld be divided into traffic areas based onthe expected amount of traffic. The threeclasses of traffic areas are—

Nontraffic.Occasional traffic.

Traffic.

Nontraffic Areas. These areas requiretreatmen t to w ithstand air-blast effects fromwind or aircraft operations and are not sub-jected to traffic of any kind. Typicalnontr affic areas includ e—

Graded construction areas.Denuded areas around the peripheryof completed construction projects.Areas bordering airfield or heliportcomplexes.

Protective petroleum, oil, and lubri-cant (POL) dikes.Magazine embankments or amm uni-tion storage barricades.Bunkers an d revetments.Cantonment, warehouse, storage, andhousing areas, excluding walkwaysand roadways.Unimproved grounds.Areas experiencing wind-borne sand.

Occasional-Traffic A reas. Besides resist-

ing helicopter rotor downwash, aircraftpropwash, and air blast from jet engines,these areas are also subjected to occasionaltraffic by vehicles, aircraft, or personnel.Vehicle traffic is limited to occasional, non-channelized traffic. Typical occasional-traffic areas include the following:

Shou lders and overru ns of airfields.




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during the dry season when the relativehum idity drops below 30 percent.

DUST-CONTROL METHODS

The four g eneral du st-control-treatmentmethods commonly used are—

Agronomic.Surface penetrant.Admix.Sur face blanket.

Agronomic

This method consists of establishing,prom oting, or pr eserving vegetative cover toprevent or r educe du st generation from ex-posed soil surfaces. Vegetative cover is oftenconsidered the most satisfactory form of dustpalliative. It is aesthetically pleasing,

durable, economical, and considered to bepermanent. Some agronomic app roachesto d ust control ar e suitable for theater-of-operations requirements. Planning construc-tion to minimize disturbance to the existingvegetative cover w ill prod uce good d ust-palliative results later.

Agronomic practices include the use of—

Grasses.Shelter belts.Rough tillage.

Ground s maintenance management and fer-tilizing will help promote the development of a solid ground cover. Agronomic methods arebest suited for nontraffic and occasional-traffic areas; they are not normally used intraffic areas.

Grasses. Seeding, sprigging, or sodd inggrasses should be considered near theater-of-operations facilities that have a projecteduseful life exceeding 6 months. Combiningmulch with seed promotes quicker estab-

lishment of the grass by retaining moisture inthe soil. Mulching materials include straw,hay, pap er, or brush . When m ulches arespread over the g-round, they p rotect the soilfrom wind and water erosion. Mulches are ef-fective in preventing dust generation onlywhen they are properly anchored. Anchoring

can be accomplished by disking or by applyingrap id curing (RC) bitum inous cutbacks orrapid setting (RS) asphalt emu lsions. Mulchis und esirable around airports and heliportssince it may be ingested into jet engines,resulting in catastrophic engine failure.

Shelter Belts. They are barriers formed byhed ges, shru bs, or trees that are high anddense enough to significantly redu ce windvelocities on the leeward side. Their place-ment should be at right angles to theprevailing winds. While a detailed discussionof shelter-belt planning is beyond the scope of this man ual, shelter belts shou ld be con-sidered for use on military installations andnear forward landing strips (FLS) con-structed for contingency pu rposes in austereenvironments (such as th ose constructed in

Central America).

Rough Tillage. This method consists of using a chisel, a lister, or turning plows to tillstrips across nontraffic areas. Rough tillageworks best with cohesive soils that form clods.It is not effective in cohesionless soils and, if used, may contribute to increased d ustgeneration.

Surface Penetran t

The surface penetration m ethod involves

app lying a liquid du st palliative directly tothe soil surface by spraying or sprinkling andallowing the palliative to p enetrate the sur-face. The effectiveness of this methoddepend s on the depth of penetration of thedust palliative (a function of palliative vis-cosity and soil permeability). Using wa ter toprew et the soil that is to be treated enhancespenetra tion of the palliative.

Surface penetrants are useful under alltraffic conditions; however, they are only ef-

fective on prepared areas (for example, onunsurfaced gravel roads). Dust palliativethat p enetrate the soil surface include—

Bitumens.Resins.Salts.Water.




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degrees Fahrenheit without heating. The tarcutbacks generally have better penetratingcharacteristics than asphalts and normallycure in a few h ours. Tars p roduce excellentsurfaces, but curing proceeds very slowly.Several days or even w eeks may be requ ired

to obtain a completely cured layer. Tars aresusceptible to temp erature changes and maysoften in h ot weather or become brittle in coldweather.

APSB, a commercial product, is a specialliquid asphalt composed of a high penetrationgrade of asphalt and a solvent blend of kerosene and nap htha. It is similar in char-acter to a standard low-viscosity, medium-curing liquid asphalt}but it differs in manyspecific properties. The APSB is suitable forapplication to soils that are relatively imper-

vious to conven tional liqu id asph alts andemu lsion systems. Silts and mod erately plas-tic clays (to a PI of 15) can be treatedeffectively. Curing time for the APSB is 6 to12 hours u nd er favorable ground tempera-ture and weather condi t ions . Onhigh-plasticity solids (with a PI greater than15), the material remains on the surface as anasphalt film that is tacky at a groundtemperature of approximately 100 degreesFahrenheit and above. The APSB mu st beheated to a temperature between 130 to 150

degrees Fahrenheit to permit spraying withan asp halt distributor.

Resins. These du st palliative may be u sedas either surface penetrants or surfaceblankets. They have a tend ency to eitherpenetrate the surface or form a th in surfacefilm d epending on the type of resin u sed, thesoil type, and the soil condition. Thematerials are norm ally applicable to nontr af-fic areas and occasional-traffic areas whereru tting w ill not occur . They are n ot recom-mend ed for use with silts and clays.

Resin-petroleum-water emulsions arequite stable and highly resistant to weather-ing. A feature of this type of dust palliative isthat the soil rema ins readily perm eable towater after it is treated. This type of productis principally man ufactured un der the trad enam e Coherex. App lication rates range from

0.33 to 0.5 gallon per square yard. Thematerial may be diluted for spraying using 4parts water to 1 part concentrate. Thismaterial is pr imarily suited for dr y sand ysoils; it p rovides u nsu itable results w henused on silty and clayey soils.

Lignin is a by-product of the manufactureof wood pulp. It is soluble in water and there-fore readily p enetrates the soil. Its volub ilityalso makes it susceptible to leaching from thesoil; thus, application is repeated as neces-sary a fter rainfall. Lignin is read ily availablein the continental United States and certainother sections of the world. It is useful inareas where dust control is desirable for shortperiods of time; it is not recommend ed for usewhere durability is an important factor. The

recommended application rate is 1 gallon persquare yard of a resinous solution of 8 percentsolid lignin sulphite.

Concrete curing compounds can be used topenetrate sands that contain little or no siltsor clays. This material shou ld be limited toareas w ith no traffic. The high cost of thismaterial is part ly offset by the low app licationrate required (0.1 to 0.2 gallon per squareyard). Standard asphalt pressure dis-tributors can be used to app ly the resin;however, the conventional spray nozzlesshould be replaced with nozzles with smalleropenings to achieve a uniform distribution atthe low application rate.

Salts. Salts in w ater emu lsions have beenused with varying success as du st palliative.Dry calcium chloride (CaC12) is deliquescentand is effective when the relative humidity isabou t 30 percent or g reater. A soil treatedwith calcium chloride retains more moisturethan the u ntreated soil und er comp arabledrying conditions. Its use is limited to

occasional-traffic areas, Sodium chloride(NaC1) achieves some dust control by retain-ing moisture and also by some cementingfrom salt crystallization. Both calciumchloride and sodium chloride are soluble inwater and are readily leached from the soilsurface; thus, frequent m aintenance is re-quired. Continued applications of salt




FM 5-410

solutions can ultimately build up a thin,crusted surface that w ill be fairly hard andfree of du st. Most salts are corrosive to metaland should not be stored in the vehicle usedfor application. Magnesium chloride(MgC12) controls du st on gravel roads withtracked -vehicle traffic. Best resu lts can be

expected in areas with occasional rainfall orwhere the hu mid ity is above 30 percent. Thedust palliative selected and the quantity usedshould not exceed local environmental protec-tion regulations.

Water. As a commonly used (but very tem-porary) m easure for allaying d ust, a soilsurface can be spr inkled w ith wa ter. As longas the ground surface remains moist or dam p,soil particles resist becoming airborne.Depending on the soil and climate, frequent

treatment m ay be required. Water shouldnot be applied to clay soil surfaces in suchquantity that pud dles forms since a mud dy orslippery surface may result where the soilremains wet.

Admix

The adm ix method involves blending thedu st palliative with the soil to produ ce aun iform m ixture. This method requ ires moretime and equipm ent than either the penetra-tion or surface blanket methods, but it has the

benefit of increasing soil strength.Norm ally, a minimu m treatment d epth of 4

inches is effective for traffic areas and 3 in-ches for other areas. The admixture can bemixed in place or off site. Typical adm ixturedu st palliative includ e—

Portland cement.Hydrated lime.Bituminou s materials.

In-Place Admixing. In-place ad mixing isthe blending of the soil and a dust palliativeon the site. The sur face soil is loosened (if necessary) to a depth slightly greater thanthe d esired th ickness of the treated layer.The dust palliative is add ed and blended withthe loosened su rface soil, and th e mixture iscomp acted. Powd ers may be spread by handor with a mechanical spreader; liquids should

be applied with an asp halt distributor.Mixing equipm ent that can be used in-cludes—

Rotary tillers.Rotary pulverizer-mixers.Graders.Scarifies.

Disk harrows.Plows.

Admixing and / or blending should continueun til a un iform color of soil and du st palliativemixture, both horizontally and vertically, isachieved. The most effective compactionequipment that can be used is a sheepsfoot orru bber-tired rollers. The p rocedu re for in-place admixing closely resembles the soilstabilization procedure for changing soilcharacteristics and soil strength u sed in road

construction. For d ust control on a non trafficarea, adequate compaction can be achieved bytrafficking the entire surface with a 5-tondual-wheel truck. For all other traffic situa-tions, the procedure should follow TM 5-822-4. This procedure is time-consumingand requires the use of more equipment thanthe other three. Following placement, admix-ing, and compaction, a minimum of sevendays is required for curing.

Two cementing-type powders (portland ce-

ment and hydrated lime) are primarily usedto improve the strength of soils. However,when they are ad mixed w ith soils in rela-tively small quan tities (2 to 5 percent by drysoil weight), the mod ified soil is resistant todusting. Portland cement is generally suitedto all soil types, if un iform mixing can beachieved, whereas hydrated lime is ap-plicable only to soils containing a highpercentage of clay. The comp acted soil sur-face should be kept moist for a minimum of 7days before allowing traffic on it.

Bituminous materials are more versatilethan cementing m aterials in providing ad e-quate d ust control and w aterproofing of thesoil. Cutbacks, emulsion asphalts, and roadtars can all be used successfully. The quan-tity of residu al bitum inous m aterial usedshould range from 2 to 3 percent of dry soil




FM 5-410

weight (for soils having less than 30 percentpassing th e Nu mber 200 sieve) to 6 to 8 per-cent (for soils having more than 30 percentfine-grained soils passing the Number 200sieve). The presence of mica in a soil isd etrimen tal to the effectiveness of a soil-bituminous material admixture. There are

no simple guides or shortcuts for designingmixtures of soil and bituminous materials.The maximum effectiveness of soil-bitum inous m aterial adm ixtures can u suallybe achieved if the soil characteristics arewithin the following limits:

The PI isThe amoun t of material passing theNum ber 200 sieve is 30 percent byweight.

This data an d add itional construction d ata

can be found in TM 5-822-4. Traffic should bedetoured around the treated area until thesoil-bituminous material admixture cures.

Cutback asphalt provides a dust-free,waterproof surface when admixed into soil todep ths of 3 inches or more on a firm subgrade.More satisfactory results are obtained if thecutback asphalt is preheated before using it.Soils shou ld be fairly d ry w hen cutback as-phalts are admixed. When u sing SC or MCtypes of cutback asphalt, aerate the soil-

asph alt mixture to allow th e volatiles toevaporate.

Emulsified asphalts are adm ixed w ith aconditioned soil that allows the emulsion tobreak before compaction. A properly condi-tioned soil shou ld have a soil moisturecontent not to exceed 5 percent in soils havingless than 30 percent passing the Nu mber 200sieve. Emulsified asphalts, particularly thecationics (CSS-1 or CSS-lb), are very sensi-tive to the sur face charge of the aggregate orsoil. When they are used improperly, theemulsion may break prematurely or aftersome delay. The slow-setting anionic emul-sions of grades SS-1 and SS-lh are lesssensitive.

Road tars with RT and RTCB grad es can beused as ad mixtures in the same manner as

10.

other bituminou s materials. Road tar ad mix-tures are susceptible to temperatur e changesand may soften in hot weather or become brit-tle in cold weather.

Off-Site Admixing. Off-site admixing isgenerally used w here in-place admixing is not

desirable and/ or soil from anoth er sourceprovides a more satisfactory treated surface.Off-site admixing may be accomplished witha stationary mixing p lant or by wind row-mixing with graders in a central workingarea. Processing th e soil and du st pa lliativethrough a central plant produ ces a moreuniform mixture than in-place admixing.The major disadvantage of off-site operationsis having to transport an d spread th e mixedmaterial.

Surface BlanketThe principle of the surface blanket method

is to place a “blanket” cover over the soil sur-face to control dust. The three types of materials used to form th e blanket are—

Minerals (aggregat es).Synthetics (prefabricated mem branesand meshes).Liqu ids (bituminou s or polyvinyl ace-tate liquids).

These materials may be used alone or in the

combinations discussed later.

The type of treatment used dictates theequipm ent required . However, in all cases,standard construction equipment can be usedeffectively to place any of the blanketmaterials. Mechanized equipm ent shou ld beused wh erever possible to assure u niformityof treatment.

The surface blanket method is app licable tonontraffic, occasional-traffic, and trafficareas. Aggregate, prefabricated mem brane,and mesh treatments are easy to place andcan withstand considerable rutting. Theother surface blanket methods onlywithstand considerable ru tting. Once a su r-face blanket treatment is torn or otherwisecomp romised and the soil exposed, sub-sequent traffic or air blasts increase the




FM 5-410

damage to the torn surface blanket andproduce dust from the exposed soil. Repairs(maintenance) should begin as soon as pos-sible to protect the material in place and keepthe d ust controlled.

Minerals (aggregates). Aggregate is ap-prop riate in arid areas w here vegetativecover cannot be effectively established . It iseffective as a du st pa lliative on non traffic andoccasional-traffic areas. The maximumrecommend ed aggregate size is 2 inches; ex-cept for airfields and heliports. To p reventthe aggregate from being picked up by theprop (propeller) wash, rotor wash, or air blast,4-inch aggregate is recommended (see Table9-28).

Prefabricated Membrane. Membrane

used to surface an area controls dust and evenacts as a sur face course or rid ing su rface fortraffic that d oes not ru t the soil. When su b-jected to traffic, the membrane can beexpected to last app roximately 5 years.Minor rep airs can be m ad e easily. For op-timum anchorage, the membrane should beextended into 2-foot-deep ditches at each edgeof the covered area; then it shou ld be staked inplace and the d itches backfilled. Furth erdetails on the use and installation of prefabri-cated membranes can be obtained from TM

5-330/AFM 86-3, Volume II.

Prefabricated Mesh. Heavy, woven jutemesh, such as commonly used in conjunctionwith grass seed operations, can be u sed ford ust control of nontraffic areas. The m eshshould be secured to the soil by burying the

edges in trenches and by using large U-shaped staples that are driven flush w ith thesoil sur face. A minimu m overlap of 3 inchesshould be used in joining rolls of mesh;covered soil should be sprayed with abituminou s m aterial. Trial applications are

recomm ended at each site and should be ad-justed to su it each job situation.

Bituminous Liquid. Single- or double-bituminous surface treatments can be used tocontrol du st on most soils. A med ium-curingliquid asphalt is ordinarily u sed to p rime thesoil before placing the surface treatment.Fine-grained soils are generally prim ed w ithMC-30 and coarse-grained soils with MC-70.After the prime coat cures, a bituminousmaterial is uniformly applied, and gravel,slag, or stone aggregate is spread over the

treated area at ap proximately 25 poun ds p ersquare yard. The types of bituminousmaterials, aggregate gradations, applicationrates, and method s of placing surface treat-men ts are d escribed in TM 5-822-8/AFM 88-6, Chapter 9. Single-or double-bituminoussurface treatments should not be u sed w hereturf is to be established.

Polyvinyl Acetate (DCA 1295) (without reinforcement). DCA 1295 has a slight od orand an appearance similar to latex paint.The mater ial is diluted 3 p arts DCA 1295 to 1.part water and cures in 2 to 4 hours und erideal conditions of moderate to high temp era-ture an d low relative hu m idity. A clear,flexible film forms on the treated surface.DCA 1295 can be sprayed w ith a conventionalasphaIt distributor provided modificationsare made to the pump to permit external




FM 5-410

lubr ications. The DCA 1295 can be u sedalone or over a fiberglass reinforcemen t. Ad-ding fiberglass does not affect the basicapplication procedures or the curing charac-teristics of the DCA 1295. This material issuitable for use on nontraffic, occasional-

traffic, and traffic areas. It is also effectivewh en sprayed over grass seed to p rotect thesoil until grass occurs. Uniform soil coverageis enhanced by sprinkling (presetting) thesurface w ith water.

Polyv inyl Acetate (DCA 1295) (w ith rein-forcement). A fiberglass scrim material isrecommen ded for use with the DCA 1295wh en a reinforcemen t is desired. Fiberglassscrirn increases the expected life of the d ust-control film by redu cing the expan sion andcontraction effects of weather extremes. The

scrim material should be composed of fiberglass threads with a plain weave patternof 10 by 10 (ten thread s per inch in th e war pdirection an d 10 threads per inch in the filldirection) and a greige finish. It should weighapproximately 1.6 ounces per square yard.Using scrim ma terial does n ot create anyhealth or safety hazards, and special storagefacilities are not requ ired . Scrim m aterialscan be app lied u nd er any climatic cond itionssuitable for dispensing the DCA 1295.(Under special conditions, continuous

strands of fiberglass maybe chopped into l/ 2-inch-long segments and blown over th e areato be p rotected.) The best m ethod of place-ment is for the fiberglass scrim material to beplaced immediately after presetting withwater, followed by the DCA 1295.

Polypropylene-Asphalt Membrane. Th epolypropylene-asphalt membrane is recom-m end ed for u se in all traffic areas. It hasconsiderable durability and withstands rut-ting up to app roximately 2 inches in d epth.

This system is a combination of apolypropylene fabric sprayed with an asphaltemulsion. Normally a cationic emulsion isused; however, anionic emulsions have alsobeen used successfully. Several types of polyp rop ylene fabric are commercially avail-able.

This treatment consists of the followingsteps:

Place a layer of asphalt (0.33 to 0.50gallon per square yard) on thegroun d, and cover this with a layerof polypropylene fabric.

Place 0,33 gallon per squ are yard of asphalt on top of the polypropylene.Apply a sand-blotter course.

This system d oes not require any rolling orfurther treatment an d can be trafficked imm-ediately.

Care should be taken d uring constructionoperations to ensure adequate longitudinaland transverse laps wh ere two p ieces of polypropylene fabric are joined. Lon-gitudinal joints should be lapped a minimumof 12 inches. On a su perelevated section, thelap should be laid so the top lap end is facingdow nhill to help prevent w ater intrusionun der th e membr ane. On a transverse joint,the minimum overlap should beat least 24 in-ches. Additional emu lsion shou ld be on thetop side of the bottom lap to p rovide enoughemulsion to adhere to and waterproof the toplap. Figure 9-31, page 9-64, illustrates thisp rocess on tangen tial sections. Ap plyingpolypropylene on roadway curves requirescutting and placing the fabric as shown in

Figure 9-32, page 9-64.The joints in curvedareas should be overlapped a minimum of 24inches.

SELECTION OF DUST PALLIATIVE

There are many du st palliative that are ef-fective over a w ide ran ge of soils and climaticconditions. Engineering judgment andmaterial availability play key roles in deter-mining the specific dust palliative to select.Tables 9-29 through 9-32, pages 9-65 through9-70, were developed from evaluation of their

actual per form an te to assist in the selectionprocess. The dust palliative and d ust controlmethods are not listed in any order of effec-tiveness.

Where no d ust p alliative is listed for a par-ticular d ust control method, none w as foun d




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Soil Stabilization for Road s and Airfields 9-66



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to be effective under those conditions. For ex-ample, for the agronomic method, a dustpa lliative is not recommend ed for a loose,sandy soil with no binder, nor is a dust pallia-tive recommend ed for the surface penetrationof a f irm, clay soil (see Table 9-29, page 9-65an d Table 9-30, page 9-66). Also, theagronom ic meth od of du st control is notrecomm ended for any tr affic area (see Table9-31, page 9-67).

In Table 9-32, page 9-68 through 9-70, num-bers representing dust palliative are listedin numerical order and separated by the dust-control method. This table includes the sug-gested ra tes of ap p lication for each d ust-palliative; for instance, gallon per squareyard for liquid spray on applications or gallonper square yard per inch for liquid (or p oundper square yard p er inch for powd ers) adm ixapplications.

Application RatesThe app lication rates should be considered

estimates, as stated abov e. Unfortu nately,

the ad mix method and some surface-blanketmethods represent a full commitment.Should failure occur after selection and place-ment, the only recourse is to completelyretreat the failed a rea, which is a lengthy andinvolved process. However, should failureoccur on a section treated with a liquid dust

pa lliative, retreatm ent of the failed area isrelatively simple, involving only a distributorand operator. A second app lication is en-couraged as soon as it is determined th at theinitial app lication r ate is not achieving th edesired results.

PlacementNo treatment is suggested for areas con-

taining large dense vegetation and/ or largedebr is. Loose soil in a wet or slurry conditionand firm soil that is wet should not be treated.

Dust problems should not exist in any of theseareas; how ever, if the areas are known du stprod ucers when dry, they should be dried orconditioned and then treated.

Dilution

Several dilution ratios are mentioned forsome liquid dust palliatives. The ratios arepresented as volume of concentrate to volum eof water and should be viewed as a necessaryprocedure before a particular liquid can besprayed. The water is a necessary vehicle toget the du st palliative on th e ground . Thestated application rate is for the d ust p allia-tive only. When h igh dilu tion ratios arerequired to spray a d ust palliative, extra careshould be taken to prevent the mixture fromflowing into adjacent areas where treatmentmay be unn ecessary and / or into drainageditches. Two or more app lications may be




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transported easily are practical. Prefabri-cated fencing is desirable because it can beerected quickly and economically. Becausethe wind tends to underscore and underminethe base of any obstacle in its flow path , thefence shou ld be installed abou t 1 foot aboveground level. To maintain the effectivenessof the fencing system , a second fence shou ldbe installed on top of the first fence on thecrest of the sand accum ulation. The entirewindw ard su rface of the du ne should be stabi-lized with a dust-control material, such asbituminous material, before erecting the firstfence. The old fences shou ld not be rem ovedduring or after the addition of new fences,Figure 9-34 shows a cross section of a stabi-lized d un e with porou s fencing. As long as thefences are in place, the sand remains trapped.If the fences are remov ed, the san d soonmoves downwind, forming an advancingdu ne. The prop er spacing and num ber of fen-ces required to protect a specific area can onlybe determined by trial and observation. Fig-ure 9-35 illustrates a three-fence method of control. If the supp ly of new sand to the du ne

is eliminated, migration accelerates and dunevolum e decreases. As the dune migrates, itmay m ove great distances down wind before itcompletely dissipates. An upwind fence maybe installed to cut off the new sand sup ply if the object to be protected is far down wind of the dune. This distance usually should beatleast four times the w idth of the dun e.

PanelingSolid barrier fences of metal, wood, p lastic,

or masonry can be used to stop or divert sandmovem ent. To stop sand , the barriers shouldbe constructed perpend icular to the w inddirection. To divert sand, the panels shouldbe placed obliquely or nearly parallel to thewind. They may be a single-slant or V-shapedpattern (see Figure 9-36, page 9-76). Whenfirst erected, paneling ap pears to give excel-

lent protection. H owever, panels are notself-cleaning, and the initial accumulationsmust be promp tly removed by m echanicalmeans. If the accum ulation is not removed,sand begins to flow over and around the

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barrier and soon submerges the object to beprotected. Mechanical removal is costly andend less. This method of control is u nsatisfac-tory because of the inefficiency and expense.It should be employed only in conjunctionwith a more permanent control, such asplantings, fencing, or du st p alliative. Equal-ly good p rotection at less cost is achieved withthe fencing method.

Bitum inous M aterialsDestroying dune symmetry by spraying

bituminous materials at either the center orthe ends of the du ne is an inexpensive andpractical method of sand control. Petroleum

resin emulsions and asphalt emulsions are ef-fective. The desired stickiness of the sand isobtained by diluting 1 part petroleum resinemulsion with 4 parts waters and spraying atthe rate of 1/ 2 gallon per square yard.Generally, the object to be protected shou ld bedownwind a distance of at least twice the tip-to-tip width of the dune. The center portion of a barchan dune can be left untreated, or it canbe treated and unstabilized portions allowedto redu ce in size by w asting. Figure 9-37 shows destruction of a typical barchan dune

and stabilization depending on the areatreated.

Vegetative Treatmen tEstablishing a vegetative cover is an excel-

lent method of sand stabilization. Thevegetation to be established must often bedrought resistant and adap ted to the climate


and soil. Most vegetative treatments are ef-fective only if the supply of new sand is cut off.An u pw ind an d water, fertilizers, and mu lchare used liberally. To prevent the engulfmentof vegetation, the up w ind bou nd aries areprotected by fences or dikes, and th e seed maybe protected by u sing mulch sprayed w ith abituminous material. Seed on slopes maybeanchored by m ulch or matting. Oats andother cereal grasses may be planted as a fast-growing companion crop to provide protectionwhile slower-growing perennial vegetationbecomes established. Usually the procedureis to plant clonal plantings, then shrubs (as anintermediate step), followed by long-lived

trees. There are numerous suitable vegeta-tive treatments for use in differentenvironments. The actual typ e of vegetationselected should be chosen by qualified in-dividuals familiar with the type of vegetationthat thrives in the affected area. Stabiliza-tion by planting has the advantages of perman ence and environm ental enhance-ment w herever water can be provided forgrowth.

Mechanical Removal

In small areas, sand m aybe removed byheavy equipment. Conveyor belts and power-driven wind machines are not recomm endedbecause of their comp lexity and expense.Mechanical removal may be employed onlyafter some other method has been used toprevent the accumulation of more deposits.Except for its use in conjunction with another



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method of control, the mechanical removal of sand is not p ractical or economical.

Trenching

A trench maybe cut either transversely orlongitudinally across a dune to destroy itssymmetry. If the trench is maintained, thedu ne w ill be destroyed by w astage. Thismethod has been used successfully in theArizona H ighw ay Program in the Yum aDesert, but it is expensive and requires con-stant inspection and maintenance.

Water

Water may be ap plied to sand surfaces toprevent sand movement. It is widely usedand an excellent temporary treatment.Water is required for establishing vegetativecovers. Two major disadvantages of thismethod are the need for frequent reapplica-tion and the need for an adequate andconvenient source.

Blank et CoversAny m aterial that forms a semipermanent

cover and is immovable by the wind serves to

control du st. Solid covers, though expensive,provid e excellent p rotection and can be usedover small areas. This method of sand controlaccomm oda tes ped estrian traffic as well as aminimum amount of vehicular traffic.Blanket covers may be made from bituminousor concrete pavements, prefabricated landing

mats, membranes, aggregates, seashells, andsaltwater solutions. After placement of anyof these materials, a spr ay ap p lication of bituminou s material m ay be required toprevent blanket decomposition and sub-sequent dust.

Salt Solutions

Water saturated with sodium chloride orother salts can be applied to sand dunes tocontrol dust. Rainfall leaches salts from th esoil in time. During periods of no rainfall andlow humidity (below approximately 30 per-cent), water m ay have to be add ed to the

treated area a t a rate of 0.10 to 0.20 gallon p ersquare yard to activate the salt solution.

Section IV. ConstructionProcedures

MECHANICAL SOIL STABILIZATION

This section provides a list of constructionprocedures, using mechanical stabilizationmethods, which will be useful to the engineerin the theater of operations.

On -Site Blendin g

On-site blend ing involves the followingsteps:

Preparation.

Shape the area to crown and grade.




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Cure lime-soil mixture for zero to 48hours to perm it the lime and w ater tobreak down any clay clods. For ex-tremely plastic clays, the curingperiod may be extended to 7 days.

Final Mixing and Pulverizat ion.Add the remaining lime by the ap -propriate method.Continue the mixing and pulveriza-tion until all of the clods are brokendown to pass a l-inch screen and atleast 60 percent of the material willpass a Number 4 sieve.Add w ater, if necessary, during themixing and pulverization process.

Compaction.

Begin compaction immediately afterthe final mixing.Use pn eum atic-tired or sh eepsfootrollers.

Final curing.

Let cure for 3 to 7 days.Keep the su rface moist by p eriodicallyapplying an asphaltic membrane orwater.

Cement Stabilization

Cement stabilization involves the followingsteps:

Preparation.Shape the surface to crown andgrade.Scarify, pu lverize, and pr ewet th esoil, if necessary .Reshap e the surface to crown a ndgrade.

Spreading. Use one of the following

methods:Spot the bags of cement on the run -way, empty th e bags, and level the ce-ment by raking or dragging.Apply bulk cement from self-un loading tru cks (bulk trucks) ordu mp trucks with spreaders.

Mixing.

Add water and mix in p lace with arotary mixer.Perform by processing in 6- to8-foot-wide passes (the width of the mixer) or by mixing in a windrow

with either a rotary mixer or motorgrader.

Compaction.Begin compaction immediatelythe final mixing (no more than 1should pass between mixingcompaction), otherwise cementhydrate before compactioncompleted.

afterhourandmay

is

Use pneumatic-tired and sheepsfootrollers. Finish the surface withsteel-wheeled rollers.

Curing. Use one of the following methods:

Prevent excessive moisture loss byapp lying a bitum inous material at arate of approximately 0.15 to 0.30gallon per squar e yard.Cover the cement with about 2 inchesof soil or thoroughly wetted straw .

Fly-Ash Stabilization

The following construction procedures for

stabilizing soils ap ply to fly ash, lime-fly ashmixtures, and lime-cemen t-fly ash mixtures:

Preparation.Shape the surface to crown andgrade.Scarify and pulverize the soil, if necessary.Reshape the surface to crown andgrade.

Spreading. Use one of the following:

Spot th e bags of fly ash on th e road orairfield; empty the bags intoindividual piles; and distribute the flyash evenly across the surface w ith arake or harrow .App ly fly ash or a fly ash mixture inbulk from self-unloading trucks (bulk




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trucks) or dump trucks withspreaders.

Mixing.

Begin m ixing op erations w ithin 30minu tes of spreading the fly ash.

Mix the soil and fly ash thoroughly byusing a rotary m ixer, by w indrowingw ith a m otor grader, or by using adisk harrow.Continu e to mix un til the m ixtureappears uniform in color.

Compaction.

Add water to bring the soil moisturecontent to 2 percent above the OMC.Begin compaction immed iately follow-ing final mixing. Compaction must be

completed within 2 hours of mixing.Minimum compactive effort for soilstreated with fly ash is 95 percent of the maximum dry density of themixed m aterial.Reshape to crown and grade; thenfinish compaction with steel-wheeledrollers.

Curing. After the fly ash treated lifts havebeen finished, protect the surface from dryingto allow the soil material to cure for not lessthan 3 days. This maybe accomplished by—

App lying w ater regularly throughou tthe curing period.Covering the amended soil with a 2-inch layer of soil or thorough ly wettedstraw.App lying a bitum inous material atthe rate of app roximately 0.15 to 0.30gallon per squ are yard.

Bitumin ous StabilizationIn-place stabilization using bituminous

materials can be p erformed with a travelingplant mixer, a rotary-type mixer, or a blade.The methods for u sing these mixers are out-lined below:

Traveling

Shapwhich

Want Mixer.

and compact the roadbed onthe m ixed material is to be

placed. A prime coat should be ap-plied on the roadbed and allowed tocure. Excess asphalt from the p rimecoat should be blotted w ith a light ap-plication of dry sand.Hau l aggregate to the job and wind -

rowed by hau ling tru cks, a spreaderbox, or a blade.Add asphalt to the wind row by anasphalt distributor truck or add edwithin the traveling plant mixer.Use one of the several types of single- or m ultiple-pass shaft mixersthat are available.Work the m aterial un til about 50percent of the volatiles have escaped.A blade is often used for thisoperation.Spread the aggregate to a u niform

grade and cross section.Compact.

Rotary Mixer.

Prepare the roadbed as explainedabove for the traveling plant mixer.Spread the aggregate to a u niformgrade and cross section.Add asphalt in increments of about0.5 gallon per square yards and mix.Asphalt can be add ed w ithin themixer or with an asphalt distributor

truck.Mix the aggregate by one or morepasses of the mixer.Make one or m ore passes of the mixerafter each ad dition of asphalt.Maintain th e surface to the grad e andcross section by using a blade dur ingthe mixing operation.Aerate the m ixture.

Blade Mixing.

Prepare the roadbed as explained

above for the traveling plant mixer.Place the material in a windrow.App ly asphalt to the flattenedwindrow with a distributor truck. Amu ltiple application of asphalt couldbe used.Mix thoroughly with a blade.Aerate the mixture.


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