Return to IndexChapter 2Design and Control of Bituminous MixturesUsing a Modified Marshall Design Procedure1. General ScopeThe Department has established procedures for the design and control of bituminous concretebased on Marshall Method for more than 30 years. Since the late 1990’s, the Department hasestablished a goal of implementing a newer mix design method, referred to as Superpave;based on more current national research (SHRP). (See Chapter 2A). Until such time as fullimplementation can be realized, the Department will continue to provide and publish for usethe Modified Marshall Method. However, it is important to recognize that the Department’sultimate goal is to use only one Hot-Mix Asphalt (HMA) design procedure. Therefore it isanticipated that in the very near future, the Marshall Method will not be referenced for use bythe Department, in this context. The Modified Marshall Method will continue to be utilizedin its’ current context for Cold Bituminous Mixture Designs, until such time that anothermethod is proven more suitable.The design of bituminous mixture by the Department’s Modified Marshall Method involvesthe proportioning of the aggregates and asphalt to produce a mix that will have the optimumqualities and properties. The purpose is to develop a design, by trial means, which willcontain an optimum amount of asphalt, have adequate voids, satisfactory flow properties andpossess a planned combination of stability, durability and flexibility, based on the climaticcondition, traffic density and loads it is intended to carry.1.1 DefinitionsStability is a measure of resistance to deformation. It is necessary to have sufficientstability to meet the requirements of traffic without mat distortion, or displacement.There are two forms of resistance, frictional or interlocking and cohesive resistance.Frictional or interlocking resistance is dependent on the aggregate framework. Cohesiveresistance develops in the asphalt binder portion of the mix. It depends on the rate ofloading, load and temperature. High stability is undesirable if it is due to low VMA(voids in the mineral aggregate) or due to being deficient in asphalt binder. Suchsurfaces have low resistance to cracking, are brittle in the winter, and tend to ravelunder traffic.Durability is a measure of resistance to disintegration by weather or traffic conditions.The most important factor with respect to durability is the amount of asphalt binder. Abituminous mixture is resistant to action of air and water in direct proportion to thedegree that they are kept out of the mix. It is, however, desirable that the mix shouldcontain as high a asphalt binder content that is consistent with stability and voids. Thiscan be achieved with high VMA. This will give the pavement maximum durability andprevent raveling because of a deficiency of asphalt binder. This asphalt binder contentis referred to as the optimum.Flexibility is the ability of the bituminous mixture to bend repeatedly without crackingand to conform to changes in the base course. To have flexibility, a mix must contain2-1

the proper amount of asphalt binder. Open graded mixes are more flexible than densegraded mixes.Voids are the air spaces within the mixture. It is important that a mix contains sufficientvoids to provide spaces for expansion of asphalt binder and a slight amount ofadditional densification (compaction) under traffic. Very high air voids are alsodetrimental to the mixture because the hardening of asphalt will be accelerated resultingin brittle pavement and reduced service life.Voids in the Mineral Aggregate (VMA) is the intergranular space between theaggregate particles in a compacted mixture. This space is partially filled with asphaltbinder, the remaining space is the unfilled air void. The VMA in a mixture should beadequate to accommodate sufficient volume of asphalt binder for durability andsufficient volume of air voids as explained earlier.Flow is an index of plasticity or the resistance to distortion. The amount of asphaltbinder that fills the aggregate voids affects the flow. The flow value increases as theasphalt content of the mixture increases. Flow values will increase rapidly with smallincreases in asphalt in mixes which contain a large amount of filler.Workability is the property that determines the efficient placement without segregationand compaction of the mixture. Harsh or stiff mixtures can result from (a) excess ofcoarse aggregate, (b) low VMA. (c) low asphalt content or (d) excess of minus 75 μm(No. 200) fraction.Friction Number is a measure of the sliding force exerted on a tire when the brakes arelocked. Bituminous wearing courses must have the highest possible friction numberobtainable with the combination of aggregates available in the area. The type of coarseaggregate has the greatest effect on friction number. Aggregates which polish rapidlyand repeatedly produce low friction numbers before the normal service life is completeshould not be used. An excessive asphalt content can produce a flushed surfaceresulting in low friction number.Optimum Asphalt Content is the content determined by taking into consideration themaximum specimen specific gravity and void requirements. This procedure isexplained later. This computed optimum asphalt content may be modified by suchspecific requirements as climate, traffic density, absorptive aggregate, friction number,workability and flexibility as explained in the procedure. The final recommendedoptimum asphalt content shall meet all Marshall criteria.1.2 Desirable Mix Properties. The final mix design should be workable and contain themost suitable gradation and amount of asphalt binder to produce a mix that embodiesthe best possible combination of all parameters.Mixtures with high VMA are preferred because of the following advantages:(a) More asphalt can be incorporated in the mixture to increase durability.2-2

(b) Lower sensitivity to variation in asphalt content during production. Mixtures withlow VMA will flush if slightly excessive in asphalt content, and will be dry andbrittle if slightly deficient in asphalt content.(c) More flexibility and increased resistance to low temperature shrinkage cracking.An increase in VMA can be achieved by one or more of the following steps:(a) The gradation of the fine aggregate should be changed so that the combined mixgradation is deliberately made to deviate further, preferably on the lower side,from the maximum density line (plotted on TR-448A). This can be done by eitherchanging the percentage passing 2.36 mm (No. 8) sieve for the combinedaggregate and/or changing the blend proportions of the fine aggregates if morethan one are used.(b) If the mix contains natural sand as the fine aggregate, incorporate somemanufactured angular sand or other crushed stone fine aggregate or slag sand sothat different particle shapes are mixed. Usually, 20-25 percent angular fineaggregate is helpful to open up the mix.(c) Reduce the Percent Passing 75 μm (No. 200) sieve in the mix.2. Design Procedures2.1 Review of Job-Mix Formula (JMF). The contractor will be solely responsible todesign a mix that meets all Department requirements. The contractor will submit therequired test results, the composition of the mixtures and the combined aggregategradation curves proposed for use in the production of the base, binder and wearingcourses, to the District Materials Manager/Engineer (DMM/DME) for review prior* tothe scheduled start of work. Submit mix designs to the DME/DMM for reviewfollowing the procedures outlined in Appendix J. The acceptability of the bituminousconcrete produced from any mix design is determined as specified in Publication 408,Section 401.*NOTE: As a standard practice it is recommended to allow up to three weeks leadtime to allow for resolution of problems concerning mixture acceptability.Whenever the contractor's gradations and calculations do not check, the DMM/DMEshall request the contractor to do additional testing and/or recalculate and submit thecorrect mathematical solutions. The DMM/DME may request, at his option, to observetesting of a trial mix. He may also request that materials be submitted to the Materialsand Testing Division for evaluation of the mix.2.2 Development of the Initial Design. For a design being developed from new sources ofmaterials, past experience shall be used in determining the starting formula, or one thatapproaches the median of the specification limits. The following is the general outlinefor development of the initial design:2-3Change 5

Step 1. Obtain representative samples of all materials.(a) Determine Dry Bulk Specific Gravity of coarse and fine aggregates (AASHTOT 85 and AASHTO T 84). At least five determinations should be made for eachaggregate type using five samples, and the average value used. If the aggregatesupplier has past historical test data, the average of those values can be obtainedand used instead.(b) Determine the Apparent Specific Gravity of mineral filler, if added separately(AASHTO T 133). At least three determinations should be made and the averagevalue used.(c) Determine Specific Gravity of Asphalt @ 25 oC (77F)(Specific Gravity @ 16 oC (60F) - 0.007). (AASHTO T228).Step 2. Dry the aggregates and separate them into the specified individual sieve sizes.Step 3. Make three mixtures using the combined gradation and the asphalt content ofthe selected starting formula (Refer to Appendices A, B and D and PTM No.705 for blending and mixing procedures). Extract these samples to determine ifthe average extracted gradation conforms reasonably with the starting formulagradation. If the aggregate particles are significantly coated with fines, theextracted gradation is usually finer on the smaller sieves because the fines arepicked up. This would require appropriate adjustments to the weights of theaffected sieve size fractions.Step 4. Determine the Maximum Specific Gravity for the completed mix (AASHTOT209), and calculate total mass of mix ([490 ml] x [Maximum SpecificGravity]) to produce a compacted specimen 63.5 mm (2-1/2 inches) high.Step 5. Calculate the required amount of aggregate for the individual sieve sizes and therequired amount of asphalt binder to make 27 Marshall specimens ([9 mixturetypes] x [3 replicates]) with the following variables:(a) Passing 2.36 mm (No. 8) sieve - 3 to 5 percent less than the starting formula.(b) Passing 2.36 mm (No. 8) sieve - at the starting formula.(c) Passing 2.36 mm (No. 8) sieve - 3 to 5 percent more than the starting formula.(d) Asphalt Content - 0.3 to 0.5 percent less than the starting formula.(e) Asphalt Content - at the starting formula.(f) Asphalt Content - 0.3 to 0.5 percent more than the starting formula.The percent passing 75 μm (No. 200) sieve should be held constant in these mixtrials.Step 6. Prepare these mixtures and compact Marshall specimens (PTM No. 705).2-4Change 5

Step 7. Test the specimens for thickness, specific gravity, voids, VMA, VFA, stabilityand flow (Refer PTM No. 705, PTM No. 709 and PTM No. 715).Step 8. Report the average test data for these nine mixture types on a summary sheet,and plot them on the six graphs given in the Marshall Design Summary Form(TR-448B).Step 9. Review the summarized data carefully to establish the percentage passing 2.36mm (No. 8) sieve to be used in further trials. Besides experience, this should bebased on the following considerations: (a) high VMA, (b) mix properties, suchas, voids, VMA, stability and flow that are least susceptible to variation in theasphalt content, and (c) workability.Step 10. If the VMA values are lower than desirable in these mix trials, change in thecombined aggregate gradation and/or source will be necessary to increase theVMA as explained earlier. If the VMA values are satisfactory, Proceed to thenext step.Step 11. Use the established percentage passing 2.36 mm (No. 8) and a asphalt contentcorresponding approximately to 4 percent air voids in the further mix trails.Keep the percentage passing 75 μm (No. 200) sieve same as starting formula.This combination will be called second formula.Step 12. Make twelve Marshall specimens ([4 mixture types] x [3 replicates]) with thefollowing variables:(a) Passing 75 μm (No. 200) sieve -2 percent less than the second formula.(b) Passing 75 μm (No. 200) sieve -2 percent more than the second formula.(c) Asphalt Content -0.4 percent less than the second formula.(d) Asphalt Content -0.4 percent more than the second formula.Step 13. Repeat Step 7.Step 14. Report the average test data for these four mixture types on a summary sheetalong with the data on the second formula for comparison.Step 15. Review the summarized data carefully to establish the percentage passing 75μm (No. 200) sieve based on the considerations given inStep 9.NOTE: If the contractor intends to use the same combination of aggregate forwhich a reviewed job-mix formula (JMF) already exists, the number of trialMarshall specimens can be reduced or eliminated at the discretion of theDMM/DME, following a written request by the producer.2-5

2.3 Determination of Optimum Asphalt Content (Final Design). So far, thedevelopment of the bituminous concrete design in the initial stages, using varyingpercentages of aggregates passing 2.36 mm and 75 μm (No. 8 and No. 200) sieves, hasbeen outlined. After the percentages passing 2.36 mm and 75 mm (No. 8 and No. 200)sieves have been established, there exists a range of asphalt content which can satisfythe Marshall design criteria specified in Pub. 408. It is necessary to determine theoptimum asphalt content to strike a balance between density, stability, % air voids, and% VMA. To have a uniform practice on the determination of optimum asphalt content,the following procedure should be followed.2.3.1Procedure for Determining Optimum Asphalt Content.Using the same combined gradation of the aggregates, prepare three Marshallspecimens each at five asphalt content levels in 0.5 percent increments. To ensurea more uniform interpretation of the Marshall design, the mixing temperatureshall be the maximum temperature 3oC ( 5oF) stated on the bituminousmaterial provider’s Bill of Lading. The compaction temperature for Marshalldesign shall be the minimum temperature 3oC ( 5oF) stated on the bituminousmaterial provider’s Bill of Lading. This is very important because discrepancies inthe values of specimen specific gravity (lab density) reported in the JMF Reportcan vary significantly when these temperatures are varied. The compactionequipment and procedure should be in strict accordance with PTM No. 705,especially the compaction pedestal.Determine the maximum specific gravity (AASHTO T209) in triplicate of themixture containing adequate asphalt content (at or slightly above the expecteddesign asphalt content). The maximum specific gravity of the remaining fourmixtures can then be calculated.Determine the following properties (based upon the average of three specimens)of the Marshall specimens at five asphalt content levels:Specific Gravity of Marshall Specimen% Air Voids% VMA%VFAStabilityFlowThe data on these properties should be plotted as points corresponding to theasphalt contents used in trials on the six graphs given in the Marshall DesignSummary, Form TR-448B (See example). In each graphical plot connect theplotted values with a smooth curve that obtains the "best fit" for all values.Aggregate blends may be encountered that will furnish erratic data such thatplotting of the typical curves might be difficult especially in the binder coursemixtures. In a majority of these cases, an increase in the number of specimenstested at each asphalt content will normally result in data that will plot as typicalcurves. Test property curves, plotted as described above, have been found tofollow a reasonably consistent pattern. Trends generally noted are outlined insubsection





2.3.2Property Trends.Specific Gravity (specimen). The specific gravity of the compacted specimenincreases with increasing asphalt content up to a certain point, after which itdecreases. If no peak is obtained, attempt additional asphalt content(s) on thehigher side.Stability. The stability value increases with increasing asphalt content up to amaximum after which the stability decreases. The curve for stability is similar tothe curve for specific gravity except that the peak of the stability curve isnormally (but not always) at a slightly lower asphalt content than the peak of thespecific gravity curve. Cases are not uncommon where no stability peak isobtained, the stability continues to increase as the asphalt content is increased. Insome cases, a relatively flat stability curve with no defined peak is obtained.Flow. The flow value increases with increasing asphalt content at a progressiverate except at very low asphalt contents. The curve is usually concave upwards.Voids in Mineral Aggregate (VMA). The VMA generally decreases to aminimum value then increases with increasing asphalt contents. The rate ofincrease in VMA with increasing asphalt contents is comparatively higher in themixtures with inherently low VMA.Voids Filled with Asphalt (VFA). The VFA increases with increasing asphaltcontent. There is a maximum VFA for each aggregate blend and compactioneffort. The VFA cannot be increased above this maximum without increasing orotherwisechanging the compaction effort. The VFA curve is usually convex upwards.Air Voids. The percent of air voids decreases with increasing asphalt content,ultimately approaching a minimum void content in much the same manner as theVFA discussed above approaches a maximum value. The air voids curve isusually concave upwards.Optimum Asphalt Content. From the curves plotted on Form TR-448B read theasphalt contents at maximum specific gravity and 4% air voids. The average ofthese 2 asphalt contents read from the curves shall be the optimum.2.3.3Final Checks. Refer back to the curves to see if this optimum asphalt contentmeets all the Marshall design criteria as follows:Stability5300 N (1200 lbs.) minimum for wearing and binderFlow6-16 units% Air Voids3-5% VMA15 minimum for ID-2 Wearing, 14 minimum for ID-3Wearing and 12 minimum for ID-2 Binder is recommended2-11

If the computed optimum asphalt content does not meet the above Marshalldesign criteria, decrease or increase the asphalt content just enough to get into thespecified range of Marshall properties such as percent air voids. A percent airvoids of 4.0 is considered optimum; however, no design submitted with less than3.0 percent air voids will be acceptable to the Department.The final design should meet the Marshall criteria in all respects. The Marshallproperties corresponding to the selected asphalt content can be determined fromthe six curves and recorded on the JMF Report.2.4 Undesirable Mix Characteristics. Although a mix may satisfy all Marshall designcriteria, it can be unacceptable because of the following considerations:2.4.1. Brittleness. Mixes with abnormally high values of Marshall stability andabnormally low flow values are undesirable because pavements of such mixestend to be more rigid or brittle and may crack under heavy volumes of traffic.This is Particularly true where base and subgrade deflections are such as to permitmoderate to relatively high deflections of the pavement. The thickness of asphaltfilm around the aggregate is very low in such mixes. Adjustments in the aggregategradation (particularly the percentages passing 2.36 mm and 75 μm (No. 8 andNo. 200 sieves) should be made to increase the VMA so that more asphalt can beincorporated in the mix. This can be done by deviating further from the maximumdensity curve (Fuller's curve). If the minus 75 μm (No. 200) content is high, areduction in this fraction will increase the aggregate voids.2.4.2. Sensitivity. Mixes with aggregate gradation close to the maximum density curve(Fuller's curve) are very sensitive to slight variations in asphalt content. Theappearance of such mixes can change from dry to gummy if the asphalt content isincreased by a slight amount (as low as 0.5 percent). These mixes may result inpavements difficult to compact which may also ravel or flush. For these reasons,such mixes should be adjusted by one of the methods previously given to increasethe VMA.2.4.3. Tenderness. These mixes tend to pull and shove during the compactionoperations resulting hairline cracking, usually consisting of transverse hairlinecracks several inches apart, sometimes accompanied by longitudinal cracking. Apoor aggregate gradation often is a leading contributor to tender (slow-setting) orunstable mixes. Tender mixes are frequently typified by:(a) An excess of the middle-size fraction in the material passing 4.75 mm (No.4) sieve. A hump in the grading curve caused by the excess sand could appearon nearly any sieve below 4.75 mm (No. 4) and above 150 μm (No. 100). Thiscondition is most critical when occurring near 600 μm (No. 30) sieve. A changein the gradation of the fine aggregate(s) is necessary to remove the hump.(b) Close proximity of the aggregate gradation to the maximum density lineand/or major portion of gradation line relatively straight. These mixes have lowVMA. Some easily compatible gravel mixes attain the desired maximumdensity (lowest possible VMA) with one or two passes of the roller, and then2-12

start to decompact and deform. A change in the gradation of the mix isnecessary to alleviate this situation.2.5 Stability. Although the asphalt content at peak stability is not utilized to calculate theoptimum asphalt percentage, stability criteria must still be met. Designs should not berecommended with stabilities less than 6900 N (1550 lb) for wearing and binder toallow for normal operational variation so that 90% of the time we may be assured ofbeing above the specification minimum of 5300 N (1200 lb).If stability adjustments jeopardize other Marshall criteria in the design so that it doesnot meet requirements, adjustments to the aggregate gradation may be in order.Normally, incorporation of angular fine aggregates in the mixture increases thestability.2.6 Design of Mixtures with PG 58-28 Asphalt Cement.(a) When PG 58-28 asphalt cement is to be used in lieu of PG 64-22 on one projectonly or in patching operations, make three Marshall specimens at the JMF asphaltcontent. If the properties, such as, stability, flow, air voids, and VMA meet thespecified Marshall design criteria, use this asphalt content. If not, proceed to thefollowing step (b).(b) When PG 58-28 asphalt cement is to be used in lieu of PG 64-22 on more than oneproject, optimum asphalt content must be determined using PG 58-28. Using the samecombined gradation of the aggregate, prepare three Marshall specimens each at fiveasphalt content levels in 0.5 percent increments (a total of 15 Marshall specimens) andfollow the procedure given earlier to determine the optimum asphalt content.3. Approved Job-Mix Formula3.1 General. The JMF is developed specifically for the plant from the reviewed laboratorydesign. This may require small adjustments to fit the plant and thus ensure productionwithin the tolerance limits. The selected laboratory design must be reproducible withinthe tolerances specified in the applicable section of the specifications (Pub 408). Thisdesign when proven in production can then be considered an approved JMF as long asthe material sources, aggregate gradations, asphalt content and test values remainwithin the specifications and specified design tolerances.If the approved JMF was developed with PG 64-22 asphalt cement and the source ofthis asphalt is changed, it is not necessary to change the JMF. However, if some othergrade of asphalt cement, such as PG 58-28 is used it is necessary to re-determine theoptimum asphalt content only (15 Marshall specimens at five asphalt contents).3.2Verification of the Job-Mix Formula. JMF verification is conducted according toPublication 408 Section 401.2. If initial JMF verification is unsuccessful, the followingprocess is recommended for further evaluation of the JMF:3.2.1. The contractor must verify the JMF with a minimum of three random samplestaken from the plant production using PTM No. 1.2-13Change 1

3.2.2. Evaluate the mix composition (gradation and asphalt content) and all Marshalltest data, such as, voids, VMA, stability, flow, etc. If it checks with the previouslyreviewed JMF mix, production may begin.3.2.3. If the Marshall test data do not meet the design criteria because the mixcomposition is substantially different than the JMF, corrective action must betaken at the plant to obtain the desired mix composition and then re-evaluate theMarshall test data.3.2.4. If the mix composition conforms to the JMF but the Marshall Data do not meetthe design criteria, perform additional testing of each material component in themix for change in properties and/or verify all test equipment is in proper workingorder, calibrated within specifications, and test procedures are performedproperly. Provide a summary report which includes findings andrecommendations to the DMM/DME for review prior to performing any workwith such a design.4. Quality Control Requirements For Mix Designs During Production. Prepare andSubmit a QC Plan to the DMM/DME for review and approval as specified in Chapter 1,Section 2.1 and Publication 408 Section 401.2. Perform all tests as required therein at thespecified frequencies. Control and documentation of mixture maximum specific gravity(Gmm) during production shall be performed as specified in Appendix I.5. HOT-MIX RECYCLING DESIGN PROCESSSTEP l - Obtain ten representative samples of the reclaimed asphalt pavement (RAP)material or milled material from different locations in the stockpile. Remove atleast 150 mm (six inches) of the material from the surface of the stockpile beforeobtaining the sample to minimize segregation effects. Scalp off and discard thematerial retained on 50 mm (2 inch) sieve. Sample size at least 5 kg (10 lbs.) eachafter scalping. Split each sample into two portions. Identify the samples (No. 1thru 10). Save ten split samples [at least 2.5 kg (5 lbs.) each] for sending to theMaterials and Testing Division (Step 4). Retain the other ten split samples at theplant for testing and designing the recycled mix.STEP 2 - Run extraction on the retained ten samples of the RAP. Use 1.02 as the specificgravity of the aged asphalt. Report the extraction results on Table 1. Save theremaining portions of the retained samples for subsequent mix designs at the plant(Step 6).STEP 3 - Select the percentage of RAP to be recycled, and determine the percentages ofvirgin aggregate(s) to meet the specification requirements. Determine typicalproperties of all virgin asphalt cements (PG 58-28, PG 64-22, etc.) from theasphalt supplier. Fill out Tables 2 and 3.2-14Change 1

STEP 4 - Submit the following to the Materials and Testing Division (BituminousLaboratory) for determining the grade of virgin asphalt cement to be used inrecycling:1.Ten split samples of the RAP (at least 2.5 kg (5 lb) each) with SampleIdentification Form 447. Number the samples 1 through 10.2.Tables 1, 2 and 3.3.Current JMF for the mix using 100% virgin aggregates.STEP 5 - The Materials and Testing Division (MTD) will evaluate the aged asphalt in theRAP after Abson recovery, and using the data from Tables 1, 2 and 3 and thecurrent JMF, the MTD will recommend the grade of virgin asphalt for recycling.NOTE: If 15 percent or less RAP is used in the BCBC and ID-2 Binder mixes, theperformance grade of neat asphalt binder specified in the current JMF canbe used and there is no need to submit the RAP samples to the MTD.2-15Change 1




STEP 6 - Obtain a sample of the MTD recommended asphalt grade from theasphalt supplier (it is advisable to keep these samples on hand in advance to savetime).Prepare 15 Marshall specimens at five different asphalt contents (use half percentincrements) bracketing the current JMF asphalt content (based on 100% virginaggregates). To facilitate the mixing of the RAP, it should be heated in an oven(for not more than 1 hours) at 127 five oC (260 10oF) unless directedotherwise. Heat the virgin aggregate(s) to a suitable temperature so that theresulting mix temperature is 127 3 oC (260 5oF). Compact the Marshallspecimens at 127 3 oC (260 5oF).Obtain the Marshall design data and report in Table 4. Plot the data on the sixgraphs (TR-448B) of the Marshall Design Summary.Submit Table 4 and TR-448B to the District Materials Engineer for review of theJMF.It may not always be possible to establish the optimum asphalt content based onthe average of the two asphalt contents at maximum specimen specific gravity and4% air voids. In such cases, it is recommended to select the asphalt content whichessentially gives the air voids content equal to the current JMF using 100% virginaggregates.If it is intended to vary the percentage of the RAP during production, develop therecycled mix designs using RAP in increments of five percentage points, such as,10, 15, 20, 25 and 30 percent. If it is desired to use 12% RAP, the asphalt contentcan be interpolated from the design values at l0 and 15% RAP.2-19




6. Mix Design Method for Cold Recycled Base Course, In-Place or Central Plant MixRecycling.6.1The following procedures shall be followed when cold recycling is to be done bythe Contractor or Department forces:1.Obtain representative samples of the RAP material by one of the followingmethods:a. From Stockpile: If the material to be recycled is stockpiled, obtain five 2.2 kg(twenty pound) bags of the milled material or RAP from different locationson the stockpile. Remove at least six inches of the material from the stockpilesurface before obtaining the sample. Scalp off the material over a (2-inchsieve).b. By Milling: If cold recy

Design and Control of Bituminous Mixtures Using a Modified Marshall Design Procedure 1. General Scope . the proportioning of the aggregates and asphalt to produce a mix that will have the optimum qualities and properties. The purpose is to develop a design, by trial means, which will . sufficient