results in a reduction of viscosity as a result of the expansion of theliquid asphalt binder. Technologies using the foaming method via anadditive include Advera Synthetic Zeolite and low-energy asphalt. Hotplant manufacturers with foaming technologies include the Terex andGencor prototypes and the Astec Double Barrel Green system. Theseare sometimes referred to as foamed asphalt or free-water systems.

The different technologies result in production temperature reduc-tions of 35°F to 100°F and thus a range of reduced fuel consumptionand emissions (1). Several WMA test sections have been successfullyconstructed in the United States. Preliminary concerns with WMAhave been assurance of adequate initial mix stiffness (rutting resis-tance) and moisture sensitivity (2). Ultimately, the objective in usingWMA is to reduce emissions and conserve natural resources withoutcompromising mixture quality or increasing mixture cost.

RESEARCH OBJECTIVES AND SCOPE

The objectives of the WMA paving demonstrations in Indio, Califor-nia, were to (a) determine if the WMA could be produced and placedat lower temperatures and yield mix properties and field compactionsimilar to those of conventional HMA; (b) construct field test sectionsso WMA and HMA performance could be compared side by side; and(c) showcase the technology to key Southern California customers.These objectives were to be accomplished by following an in-depthmaterials evaluation plan to compare the WMA and HMA perfor-mance on test sections that were produced with practically identicalmethods with the exception of temperature. HMA plant dischargetarget temperature was 330°F, and WMA plant discharge targettemperature was 275°F.

Two separate demonstration projects were performed. Both projectshave control sections consisting of typical 0.5-in. HMA with 15%reclaimed asphalt pavement (RAP) to compare WMA and HMAmix properties and performance. Table 1 shows the job mix formulafor the conventional HMA used in both demonstrations. This isan Hveem mix design that meets both California Department ofTransportation (Caltrans) (3) and Southern California Public WorksGreenbook Standard specifications (4). No mix design modificationswere made to produce the WMA. The same PG 70-10 binder, whichis the Caltrans standard for this location, was used in both the WMAand HMA mixes.

Demonstration 1. Entrance to GraniteConstruction, 15000 Monroe Street (Indio, California)

The first demonstration test section paved with WMA was theentrance road to the Granite Construction office and plant located at15000 Monroe Street in Indio, California. The extent of paving for

Laboratory and Field Evaluations of FoamedWarm-Mix Asphalt Projects

Jason Wielinski, Adam Hand, and David Michael Rausch

125

Warm-mix asphalt (WMA) is much like hot-mix asphalt (HMA), butit is produced at lower plant temperatures than conventional HMA.Key benefits of the reduced WMA production temperature include thereduction of fuel consumption and of emissions. Granite Constructionperformed two WMA paving demonstration projects from its Indio,California, facility in early 2008. Both projects were paved with WMAproduced with the free water method (Astec Double Barrel Green). Theobjectives of these demonstrations were (a) to demonstrate that WMAwith reclaimed asphalt pavement could be produced and placed at lowertemperatures while yielding mix properties and field compaction similarto those of conventional HMA and (b) to construct field test sections sothat WMA and HMA performance could be compared side by side. Theseobjectives were accomplished by producing and placing the WMA andby completing an in-depth sampling and testing program to compare theWMA and HMA paved on similar test sections and produced with similarmethods (the only exception was production temperatures). The initialfield performance of the WMA and HMA has been similar, and thelong-term performance will be monitored. The WMA demonstrationobjectives were achieved, with the WMA exhibiting mix properties andfield compaction similar to those of the HMA, with slightly lower initialstiffness, as expected. The potential rutting concern with WMA has notbeen an issue in this arid Southern California climate, and the sectionsplaced on the haul road into and out of the Indio plant have been exposedto significant truck traffic.

Warm-mix asphalt (WMA) is produced at lower temperatures thanconventional hot-mix asphalt (HMA), resulting in reductions infuel consumption and in emissions, benefits particularly important toenvironmental stewardship. The WMA can be compacted at lowertemperatures, resulting in not only a greater compaction window butalso an extended paving season. During WMA production, asphaltbinder stiffness is reduced, allowing the binder to sufficiently coataggregates at lower temperatures (1). The asphalt binder stiffnesscan be reduced by an additive in the asphalt binder mix or by foam-ing the asphalt binder. Additives include waxes, chemicals, or water,which are added to the binder to reduce the binder stiffness at mixingand compaction temperatures (1). Some of these technologies includeEvotherm, Rediset, Sasobit, REVIX, and foaming.

The foaming process is accomplished by adding a small amount ofwater to the binder. The water then turns to steam and expands. This

J. Wielinski and A. Hand, Granite Construction, Inc., 1900 Glendale Avenue,Sparks, NV 89432. D. M. Rausch, Granite Construction Co., 38000 MonroeStreet, Indio, CA 92203. Corresponding author: J. Wielinski, Jason.wielinski@heritage-enviro.com.

Transportation Research Record: Journal of the Transportation Research Board,No. 2126, Transportation Research Board of the National Academies, Washington,D.C., 2009, pp. 125–131.DOI: 10.3141/2126-15

the first WMA demonstration project was the entrance road from theoutside quarry property gate to the scale house. The section wasbroken into four lots, with two of the lots paved with conventionalHMA and two to be paved with WMA. This was a 2-in. mill and fillsection consisting of 450 tons of HMA and 650 tons of WMA. Cracksealant was applied post-milling to existing cracks on the WMA out-bound section only. The conventional HMA section at the entranceroad section was paved on February 1, 2008, and the WMA sectionwas paved on February 11, 2008. This location was selected becausethere are steep grades in both the inbound and outbound directions. Thebulk of the traffic is trucks servicing the Granite Construction Indioaggregate, HMA, and Redimix facilities. Approximately 390,000 tonsof HMA, 750,000 tons of aggregate, and 125,000 yards of Redimixare hauled over this test section annually. The location was ideal foran accelerated in-service rutting evaluation.

Demonstration 2. Avenue 40 (Indio, California)

The second demonstration test section was a portion of the newlyconstructed Avenue 40 in Indio. This demonstration took place onMarch 20, 2008. The paving consisted of 1.5-in. thick WMA andHMA surface courses. The mix used was the same 0.5-in. mix with

126 Transportation Research Record 2126

15% RAP used in the first demonstration. Six 10 ×1,800-ft long passesof WMA and two passes (one 10 ft wide, the other 12 ft wide) of HMAwere paved. The first pass consisted of WMA on the north side of theroad. The ensuing WMA sections were paved adjacent to the previousWMA pass. The first HMA pass was paved next to the southern curband gutter of Avenue 40. The final pass of HMA was paved betweenthe previous pass of HMA and the last pass of WMA. A total of1,050 tons of WMA and 550 tons of HMA was placed.

MATERIALS EVALUATION PROGRAM

The same mix design, hot plant, haul trucks, paver, compactors, crews,and methods were intentionally used to construct all of the sections.The hot plant was an Astec Double Barrel drum plant. In addition toconventional aggregate and asphalt mixture testing (asphalt content,HMA moisture, gradation, sand equivalent, and volumetrics), mois-ture sensitivity testing and laboratory rutting with asphalt pavementanalyzer (APA) testing were performed. All WMA and HMA weresampled from the mat behind the paver.

The WMA samples were tested and compacted as soon as possibleafter they had been sampled in an effort to duplicate field compactiontemperature. The haul time was <5 min for Demonstration 1 and<10 min for Demonstration 2. The immediate testing was done inten-tionally, so that the WMA samples would best replicate the mix beingplaced in the field. No reheating was performed. The HMA sampleswere collected and then compacted immediately or at a later timeafter reheating.

Mix Properties

For WMA the only property that changes during the mixing processis the binder viscosity, which is reduced as the water is introducedby the asphalt-foaming apparatus, and the initial in-place mixturestiffness is reduced due to the lower production temperature. Thereduced stiffness permits the mixing and placing of WMA at reducedtemperatures.

The data presented in the tables and figures have identificationnomenclature unique to each demonstration, lot or sublot, and com-paction method. For example, data set D1HM1M represents theDemonstration 1 (D1), first HMA lot (HM1), and the Marshall com-paction method (M). Hveem compacted WMA from Demonstration 2,Lot 2 would be identified by D2WM2H.

Table 2 shows a summary of all data obtained during each demon-stration for both HMA and WMA. Most values in the table are the

TABLE 1 Mix Design Properties of 0.5-in. NominalMaximum Aggregate Size Type A Mix with 15% RAP

Parameter Target Value Specifications

Binder grade PG 70-10 PG 70-10

Asphalt content 5.50% 5.5 ± 0.45%

Air voids 4.4% 4.0–5.0%

Hveem stability 39 37 min

Sand equivalent 62 50 min

% passing, by sieve size3⁄4 in. 100 1001⁄2 in. 97 95–1003⁄8 in. 87 80–95#4 60 55–65#8 46 41–51#16 34#30 24 19–29#50 15#100 9#200 5 3–8

TABLE 2 Data from Two WMA Demonstrations

Average Average Marshall APA MixAir Voids Air Voids AC Stability Marshall Hveem TSR Results Moisture

Section (Marshall) (Hveem) (% DWA) Rice SG (lb) Flow Stability (%) (mm) (%)

D1HM1 3.2 5.1 5.5 2.474 8,050 17.3 42 41 5.0 0.04D1HM2 3.9 5.4 5.3 2.483 6,700 17.0 46 0.06

D2HM1 1.8 3.4 5.4 2.459 7,200 14.5 47 48 7.2 0.02D2HM2 2.8 3.7 5.3 2.460 7,433 13.3 47 0.02

D1WM1 2.7 3.9 5.5 2.465 4,533 14.7 37 32 7.8 0.08D1WM2 2.4 3.8 5.5 2.465 3,633 13.3 40 0.06

D2WM1 5.5 4.8 5.3 2.459 3,000 10.3 48 37 9.4 0.08D2WM2 3.9 3.9 5.5 2.457 4,000 11.6 47 0.06

NOTE: AC = asphalt content, DWA = dry weight of aggregate, SG = specific gravity, and TSR = tensile strength ratio.

average of three replicates. Asphalt contents were very consistent forall sections, ranging from 5.3% to 5.5% by dry weight of aggregate(DWA). Considering that water is introduced to the mix during theWMA mixing process, it was of significant interest to determine ifthe moisture contents of the two mix types would be different. Theresults show no significant difference in moisture content betweenthe WMA and HMA mixes (ranging from 0.08% to 0.02%).

Three cold-feed aggregate samples were obtained during the pro-duction of each WMA and HMA section during both demonstrationprojects and were evaluated for gradation, moisture content, and sandequivalent (SE). Aggregate moisture contents did not significantlyvary, ranging on average from 1.1% to 1.7%. The results shownin Table 2 are the averages of three samples obtained during eachrespective production run for percentage passing each sieve and sandequivalent. SE values changed significantly, although the percentagepassing the #200 sieve only ranged from 5.9% to 6.3%. During the firstday of production (February 1, 2008, HMA Section 1) the averageSE value was 55. During the second and third days of production, theaverage SE values ranged from 68 to 71.

The gradation got slightly coarser from section to section, thoughit was always within specification limits. The percentage passing the3⁄8-in. sieve increased (got finer) from production of the first HMAsection to the first WMA section, and the mix became even finerduring the last section of HMA production. Essentially, the coarseportion of the mix became finer from start to finish. Conversely, thepercentage passing the #8 and #16 sieves decreased (got coarser)from start to finish. The percentage passing the 200 sieve from allsample sets was essentially the same, ranging on average from 5.9%to 6.3%. This occurrence—the coarse portion of the mix becomingfiner and the fine portion of the mix becoming coarser—essentiallyresulted in a slightly more open mix gradation. Since the gradationwas more open from mix to mix, it would be logical to expect thatlab mix air voids might increase from section to section.

Table 2 also shows air voids from each section. Material fromeach sampling point was compacted by both Marshall and Hveemmethods. The Marshall samples were compacted as soon as possible(within roughly 20 min) after being sampled behind the paver withoutany reheating (at whatever temperature the mix arrived at the lab).The Hveem samples were transported to the laboratory (within 10 minof the project) and compacted at 230°F.

There is not a strong correlation between air voids and asphaltcontent. The asphalt content was very consistent, ranging only from5.3% to 5.5% by DWA. The air void data were conversely morevariable. The opening up of the gradation from the first to last dayof paving did not result in an increase in air voids from section tosection, particularly between the first and second HMA sections. The

Wielinski, Hand, and Rausch 127

air voids actually decreased, especially between the first and secondHMA sections.

Important trends are visible in the results shown in Table 2. Exceptfor the WMA data from Demonstration 2, the air voids data movedirectionally within a section consistently for both Marshall andHveem compaction methods. The Hveem compacted samples con-sistently had higher air voids than the Marshall samples on three ofthe four sections. From this trend, the conclusion can be made thatthe laboratories were very consistent and that the changes in air voidsfrom section to section, except for the WMA in Demonstration 2, werelikely caused by material variability. Material variability was not anissue in samples within the same section (among sublots). The rangeof air voids within a section and within a compaction method is actu-ally very low. This affirms that material and laboratory variabilitywithin sections was minimal.

The laboratory air void data for the WMA placed during Demon-stration 2 did not correspond well with the other data, but that canbe explained. The temperature at the time of Marshall compactionwas recorded for all six individual specimens produced, three fromeach demonstration WMA lot. Figure 1 is a plot of laboratory air voidsversus compaction temperature. There is a visible relationship betweenlaboratory air voids and the Marshall compaction temperature. Asthe temperatures of the samples fell below 200°F at the time ofcompaction, the laboratory air voids obtained increased. For this mix,as long as laboratory compaction was completed above 225°F, morerepeatable results could be achieved, since the trend line begins toflatten beyond this temperature.

To develop a better understanding of the variability in the labo-ratory air void data, compacted mix bulk specific gravities (GMB) andtheoretical maximum densities (Rice or GMM) values were investigated.Figure 2 shows a plot of the average GMB (both Hveem and Marshall),GMM, and asphalt content from each section. The GMM value theoret-ically changes in the opposite direction of asphalt content changes.The plots show this trend exists for the data obtained, again indicatingconsistent laboratory testing procedures.

The average GMB from each section exhibits similar trends to thoseseen in the air voids data. The differences in GMB values betweencompaction methods are consistent from section to section and trackin the same direction within a section, indicating material consistencywithin a section and good lab materials-testing practices. However,the GMB values, minus the WMA from Demonstration 2, generallyincrease from section to section, while the GMM values decrease. Whenthe trends are combined, it results in the trend of lower air voids. Thismay be explained by a change in materials. Given the significantincrease in SE between the first day (D1HM1) and the other days,when the SE increased from 55 to 70, a small change in the fine

Avg. % Avg. % Avg. % Avg. % Avg. % Avg. % Avg. % Avg. % Avg. % Passing Passing Passing Passing Passing Passing Passing Passing Passing1⁄2″ 3⁄8″ #4 #8 #16 #30 #50 #100 #200 Avg. SE

96 84 63 49 37 25 16 11 6.3 55.3

97 88 62 46 33 24 16 11 5.9 71.3

97 86 63 48 35 25 16 11 6.0 67.7

97 84 62 45 33 23 16 11 6.1 70.7

128 Transportation Research Record 2126

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

150 160 170 180 190 200 210 220 230 240 250

Compaction Temperature (F)

Lab

Air

Vo

ids

FIGURE 1 Lab air voids versus compaction temperatures for WMA (Demonstration 2).

2.300

2.310

2.320

2.330

2.340

2.350

2.360

2.370

2.380

2.390

2.400

2.410

2.420

2.430

2.440

2.450

2.460

2.470

2.480

2.490

2.500

D1HM1 D1HM2 D1WM1 D1WM2 D2WM1 D2WM2 D2HM2D2HM1

Sample

Sp

ecif

ic G

ravi

ty

4.0

4.2

4.4

4.6

4.8

5.0

5.2

5.4

5.6

5.8

6.0

Asp

hal

t C

on

ten

t D

WA

(%

)

Avg GMB Marshall

Avg GMB Hveem

GMM

% AC

WMA 1 HMA 2HMA 1 WMA 2

FIGURE 2 Bulk and Rice specific gravities and asphalt content results.

material characteristics combined with the small change in gradationcould have affected the compactability of the mix and influenced themixture GMB values. This change in material could also significantlychange the overall specific gravity of the aggregate blend, resultingin a change in GMM values. The WMA 2 section cannot be accuratelycompared with the other sections because of the aforementioned lowcompaction temperatures.

Marshall and Hveem material properties were evaluated by demon-stration, mix type, and lot. The average values for each section areshown in Table 2. The Marshall stability values for each type of mix(HMA or WMA) are consistent. The HMA Marshall stability valuesrange from 6,600 to 8,000 lb, whereas the WMA results range from3,000 to 4,500 lb. This is very likely explained by the lower mixstiffness caused by the lower mix production temperature (thus lessbinder production aging). All measured Marshall stabilities for HMAand WMA exceeded the design criteria of 1,800 lb for a 75-blowMarshall mix design in accordance with MS-2 (5). As expected, thetrends that were observed from Marshall stability were also seen inMarshall flow for the majority of the data.

The Hveem stability results did not track as well as their Marshallcounterparts. The Hveem stability results for the HMA were con-sistent, ranging from 42 to 47. The WMA Hveem stability valuesfrom Demonstration 1 were lower than the HMA results, similar tothe Marshall stability results. The WMA sampled during Demon-stration 2 on average had the highest Hveem stability results. On thebasis of the available data, including air voids and bulk specificgravity, it is assumed that this issue is associated with the reheatingof the mix. All stability test results met the specification minimums.

Both WMA and HMA were also evaluated for moisture sensitivity—tensile strength ratio (TSR)—and rutting susceptibility. The TSR test(AASHTO T 283) is an indicator of stripping potential, which occurswhen water interrupts the bond between the asphalt binder and theaggregate. This can result in the stripping or raveling, or both, of theoverall pavement section. Since water is being introduced to the mixduring the WMA process, it was considered paramount to determineif there were any detrimental effects on stripping potential.

The TSR results are shown in Table 2. Both the conventional HMAand WMA performed similarly in the TSR test. The typical minimumrequired TSR value for HMA is 70% to 80% (AASHTO M-323). TheHMA samples had TSR values ranging from 41% and 48%. TheWMA TSR results were from 32% and 37%, about 10% lower thanthose for the HMA. Generally, materials with TSR results this lowrequire an anti-strip agent, although at the time the local specificationsdid not require it. The values appear low but are typical of HMA thatis successfully used in this arid region. Both the HMA and WMATSR results from Demonstration 1 were lower than the TSR resultsof their counterparts from Demonstration 2. This may be explainedby the increase in SE from Demonstration 1 to 2.

Rutting susceptibility was evaluated with the APA laboratorywheel-tracking device (AASHTO TP 63-07). It was important toquantify the difference in rutting susceptibility between the HMAand WMA samples because of the nature of WMA production andthe theory that WMA mixes may be more susceptible to prematurerutting. The samples used for this testing were compacted to a heightof 3 in. with a Superpave® gyratory compactor and delivered to theUniversity of Nevada Reno for testing. Testing was performed at70°C for 8,000 cycles.

The APA results show that the WMA in both cases had slightlyhigher average rut depths than the HMA sections. The WMA aver-age of 8.8 mm is not significantly higher than the HMA average of6.5 mm, given that the testing was performed at 70°C. The APA

Wielinski, Hand, and Rausch 129

rutting performance was acceptable for both the HMA and WMA.Similar to the TSR results, the APA results from Demonstration 1 werelower than the APA results from Demonstration 2, which might alsobe explained by material variability between demonstration projects.

Reheating of WMA Material for APA Testing

WMA material from Demonstration 2 was also sampled, stored, andreheated to mix design compaction temperature. This material wascompacted to the required 3-in. height requirement by the Superpavegyratory compactor necessary for APA testing. These samples weretargeted to have relatively the same air void content as the samplescompacted immediately after sampling. The results from the APAtesting for the reheated samples were on average 2.8 mm. As shown inTable 2, the results for the immediately compacted pills were 9.4 mm;hence rut depth decreased if the samples were reheated, as expected.This raises a question on reheating and compacting of WMA andwhether the results would be representative of the mix placed inthe field.

IN-PLACE COMPACTABILITY AND DENSITY RESULTS

The second objective of the project entailed comparing and contrast-ing the compaction of WMA to HMA in the field. For all sections thesame hot plant, truck type, paver, crews, and compaction equipmentwere employed. The target hot plant mix discharge temperature for theHMA was 330°F and for WMA 275°F. Plant discharge tempera-tures were reported to be within ±10°F of the target values. Mix wasproduced at roughly 300 ton/h and was only stored in silos for veryshort times, since the hot plant was dedicated to the demonstrationprojects each paving day. Mix was transported in end dump trucks anddumped directly into the hopper of the Terex paver. Haul time fromthe plant was <5 min to the Demonstration 1 location and <10 minto the Demonstration 2 location.

During Demonstration 1, the temperature of the conventional HMAmix at paver discharge ranged from 270°F to 290°F for the HMAoutbound section. The WMA paved during Demonstration 1 had truckdischarge temperatures between 215°F for the inbound sectionsand 265°F for the outbound sections. Paving commenced at about 9 a.m. and was completed within 3 h each day. Morning ambientair temperatures on February 1 ranged from 49°F at 9 a.m. to 61°Fat 1 p.m. During the WMA paving on February 11, the temperaturerecorded at 9 a.m. was 66°F and at 1 p.m. was 82°F. Table 3 showssurface temperatures recorded during various steps in the compactionprocess. Figure 3 shows the breakdown compaction of one of theHMA (3b) and one of the WMA (3a) sections. Note the heavy steamrolling off the much hotter HMA section and less steam coming offthe cooler WMA section.

The compaction effort applied to both the conventional HMA andWMA sections was identical (i.e., same rollers, same rolling pattern)to determine if the WMA would compact differently than the con-ventional HMA. The 2-in. lifts were compacted with the same Sakai652 (8-ton) steel drum roller for breakdown compaction and a tandemSakai 502 (4-ton) steel drum and pneumatic roller for intermediateand finish compaction. Three passes were made with the Sakai 652roller for breakdown compaction. Three passes of the tandem rollerwere made to complete intermediate and finish rolling. This rollerpattern was previously established for the HMA and intentionallynot modified throughout the demonstrations.

Three cores were taken from each section and tested for in-placedensity. The compaction results, also presented in Table 3, are basedon GMM. The results show that the WMA actually was compactedcloser to 93.0% of the GMM, while the HMA sections averaged 92.1%.Typical specifications require an in-place density of at least 92%of GMM. This data suggest that under the same compactive effort, theWMA compacted more readily at lower temperatures.

The ambient air temperature recorded at the beginning of Demon-stration 2 was 55°F, and there was a steady light breeze. Additionalambient air temperature readings and temperature readings of the matat paver discharge and during compaction are shown in Table 3 withthe in-place density results.

The temperatures of the material at paver discharge were alsochecked periodically throughout the morning. The WMA paver dis-charge temperature near the first location tested for density was 270°F.The next two WMA mix temperature measurements on paver dis-charge were 256°F and 252°F. The last recorded WMA truck dischargetemperature near density test Location 7 was 262 °F. The target plantdischarge temperature was 275°F, and the actual discharge was280°F to 270°F.

The compaction effort (rolling pattern) was initially set to match thecompaction effort of Demonstration 1 even though the lift thicknesswas decreased from 2 in. to 1.5 in. The same Sakai 652 was used forbreakdown compaction and was followed by the Sakai 502 tandemfor intermediate and finish rolling. Again, three passes of each rollerwere used as the initial compaction effort. This scenario was changedthroughout the day a couple of times on the basis of readings from thenuclear gauge. After completion of three of the WMA paving passes,the Sakai 652 was replaced with a Sakai 800 (11.5-ton) roller to com-plete breakdown compaction. The Sakai 652 was also introduced as

130 Transportation Research Record 2126

a third roller to perform intermediate rolling between the Sakai 800and the Sakai 502 tandem. Initial results were inconclusive, and obser-vations made included movement of the mat under the drums andminor checking, which led to the removal of the Sakai 652 roller.

Similar to Demonstration 1, the density of the pavement was mon-itored throughout the day with the same Campbell-Pacific Nucleargauge. Cores were taken near the locations tested with the nucleargauge to permit comparisons. The core results are summarized inTable 3. The compaction test results from Location 9 are of interestbecause of its relatively low core density. Temperature data recordedat this location show that intermediate compaction did not start untilthe surface temperature was down to 167°F. Further investigationof this mix may show that this temperature is too low to begin inter-mediate compaction. Less than three passes from the tandem rollerwere performed at this location. These factors explain the low densityfor this location.

In-place density measurements were made at two locations for theHMA placed on Avenue 40. The data are summarized in Table 3. TheHMA temperature on paver discharge during the final paving passesof the day ranged from 295°F to 290°F. The cores taken from theselocations had densities of 93.8% and 94.0% for an average of 93.9%.When these numbers are compared to the values obtained for theWMA place on Avenue 40, it is apparent that the HMA and WMAexhibited similar compactability. The averages of the uncorrectedin-place densities of 90.8% for the HMA and 91.1% for the WMAare very close. Furthermore, the averages for percentage of com-paction based on the core data were higher than the uncorrectedin-place densities for both the WMA and HMA samples. The HMAcore densities were higher (93.9%) than the WMA average (92.9%).As with the previous demonstration, compaction of the WMA—with

TABLE 3 Temperature Recordings and Density Results from Demonstrations

Paver Temp at Temp at AverageAmbient Discharge Breakdown Intermediate In-Place Density In-Place

Demo Mix Type Location # Tonnage Temp (°F) Temp (°F) (1st pass) (°F) (1st pass) (°F) (cores) (% of GMM) Density

1 HMA inbound 1 450 49 92.2 92.12 52 93.93 56 91.9

HMA outbound 1 59 275a 220a,b 206a 91.32 60 93.53 61 90.0

WMA inbound 1 650 66 233a 190a 91.9 93.02 72 94.33 78 92.9

WMA 1 79 243 202 180 92.1outbound 2 81 92.8

3 82 93.9

2 WMA 1 1,050 55 270 200 175 95.1 92.92 256 200 178 94.63 67 252 200 170 93.14 200 187 92.95 79 232 198 92.66 92.47 262 186 92.78 85 218 190 92.79 167 89.4

10 182 93.911 92.6

HMA 1 550 290 93.8 93.92 295 285 94

aTemperatures were recorded once per section and were not taken necessarily at core locations.bTemperature was taken after the second pass of the breakdown roller.

the same rolling pattern, crew, and equipment, although at lowertemperatures—yielded results similar to those of the conventionalHMA pavement section.

INITIAL FIELD PERFORMANCE

Initial performance of the WMA at both locations was excellent at thetime of this writing (after about 5 months of service). No measur-able rutting has occurred at either demonstration site, and no mois-ture damage was apparent. Moisture damage is not typically an issuewith HMA from this source, although TSR values are relatively lowbecause of the arid climate.

One early observation (after about 2 weeks) was that the WMAmats appeared to be darker by visual observation than the com-panion HMA mats. The crack sealer placed after milling only at theDemonstration 1 site under WMA did not swell during placementof post-construction.

Field performance will continue to be monitored, and additionalWMA will be produced to evaluate the WMA technologies withdifferent source materials in different environments.

Wielinski, Hand, and Rausch 131

CONCLUSIONS

On the basis of the two demonstration projects constructed, it appearsthat conventional mix design methods can be used to design WMAvia the free-water technology. The Hveem and Marshall propertiesof the HMA and WMA produced were similar, and all productionWMA and HMA properties met the Hveem design and productionmix property (volumetrics and stability) requirements. Marshall airvoids were lower than Hveem air voids. When compacting WMAwith the Marshall method, temperature at the time of compaction isa very important factor. The data presented showed that when theWMA temperatures fell below 225°F at the time of compaction, theresulting laboratory air voids and mix properties were inconsistent.

The WMA possessed lower initial stiffness, as indicated by lowerHveem stability, Marshall stability and flow, and higher APA rut tests,as expected. However, all WMA wet mix met minimum mechanicalproperty requirements. This is logical because of the lower WMA pro-duction temperature, which reduced binder stiffening in productionand corresponding mix stiffness. Both the HMA and WMA sectionshad low TSR results, with the WMA results being slightly lower thanthose of the HMA. The public agencies should require an anti-stripagent, producing a TSR > 70% in this region, as one public agencydoes now.

The in-place densities observed for the WMA and HMA were verysimilar for both demonstrations. The paving crew indicated that theWMA behaved very much as the HMA, but at lower temperatures. Thepercentage of compaction achieved, on the basis of core densities forall test sections, is shown in Table 3. There was less variability in theWMA in-place densities than in those of the HMA. Furthermore,the average in-place density of the WMA and HMA demonstrationswas essentially the same (93%). For the WMA used on these demon-strations, the mix could be compacted down to about 170°F. Again,these results were achieved with the same crew, equipment, and rollingpatterns and under similar weather conditions. The constructabilityobjective of this demonstration was achieved. The WMA produced andplaced in Indio was compacted the same way that conventional HMAis compacted, even though the WMA was produced and compactedat about 50°F lower.

Finally, on the basis of the information presented herein, it appearsthat the demonstration objectives—(a) determining if the WMA couldbe produced and placed at lower temperatures and yield similar mixproperties and field compaction to those of conventional HMA;(b) constructing field test sections so WMA and HMA performancecould be compared side by side; and (c) showcasing the technologyto Granite and its key Southern California customers—have at leastbeen preliminarily achieved.

REFERENCES

1. Prowell, B., and C. Hurley. Warm Mix Asphalt: Best Practices. NationalAsphalt Pavement Association, Lanham, Md., 2007.

2. Hurley, C., and B. Prowell. Evaluation of Potential Processes for Usein Warm Mix Asphalt. Journal of the Association of Asphalt PavingTechnologists, Vol. 75, 2006, pp. 41–90.

3. Standard Specifications. California Department of Transportation, Sacra-mento, 2006.

4. Greenbook Standard Specifications for Public Works Construction. BNIPublications, Vista, Calif., 2006.

5. Mix Design Methods for Asphalt Concrete (MS-2), 6th ed. Asphalt Institute.Lexington, Ky., 2007.

The Characteristics of Nonbituminous Components of Bituminous Paving MixturesCommittee sponsored publication of this paper.

(a)

(b)

FIGURE 3 Steam rolling off (a) WMA section and (b) HMA sectionduring breakdown compaction.