Laboratory and Field Evaluations of Foamed Warm-Mix Asphalt Projects

  • Published on
    16-Dec-2016

  • View
    214

  • Download
    1

Transcript

<ul><li><p>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.</p><p>The different technologies result in production temperature reduc-tions of 35F to 100F 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.</p><p>RESEARCH OBJECTIVES AND SCOPE</p><p>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 330F, and WMA plant discharge targettemperature was 275F.</p><p>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.</p><p>Demonstration 1. Entrance to GraniteConstruction, 15000 Monroe Street (Indio, California)</p><p>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</p><p>Laboratory and Field Evaluations of FoamedWarm-Mix Asphalt Projects</p><p>Jason Wielinski, Adam Hand, and David Michael Rausch</p><p>125</p><p>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.</p><p>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.</p><p>The foaming process is accomplished by adding a small amount ofwater to the binder. The water then turns to steam and expands. This</p><p>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.</p><p>Transportation Research Record: Journal of the Transportation Research Board,No. 2126, Transportation Research Board of the National Academies, Washington,D.C., 2009, pp. 125131.DOI: 10.3141/2126-15</p></li><li><p>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.</p><p>Demonstration 2. Avenue 40 (Indio, California)</p><p>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</p><p>126 Transportation Research Record 2126</p><p>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.</p><p>MATERIALS EVALUATION PROGRAM</p><p>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.</p><p>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 </p></li><li><p>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%).</p><p>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.</p><p>The gradation got slightly coarser from section to section, thoughit was always within specification limits. The percentage passing the38-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 occurrencethe coarse portion of the mix becomingfiner and the fine portion of the mix becoming coarseressentiallyresulted 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.</p><p>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 230F.</p><p>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</p><p>Wielinski, Hand, and Rausch 127</p><p>air voids actually decreased, especially between the first and secondHMA sections.</p><p>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.</p><p>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 200F at the time ofcompaction, the laboratory air voids obtained increased. For this mix,as long as laboratory compaction was completed above 225F, morerepeatable results could be achieved, since the trend line begins toflatten beyond this temperature.</p><p>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.</p><p>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</p><p>Avg. % Avg. % Avg. % Avg. % Avg. % Avg. % Avg. % Avg. % Avg. % Passing Passing Passing Passing Passing Passing Passing Passing Passing12 38 #4 #8 #16 #30 #50 #100 #200 Avg. SE</p><p>96 84 63 49 37 25 16 11 6.3 55.3</p><p>97 88 62 46 33 24 16 11 5.9 71.3</p><p>97 86 63 48 35 25 16 11 6.0 67.7</p><p>97 84 62 45 33 23 16 11 6.1 70.7</p></li><li><p>128 Transportation Research Record 2126</p><p>3.0</p><p>3.5</p><p>4.0</p><p>4.5</p><p>5.0</p><p>5.5</p><p>6.0</p><p>6.5</p><p>7.0</p><p>150 160 170 180 190 200 210 220 230 240 250Compaction Temperature (F)</p><p>Lab </p><p>Air V</p><p>oids</p><p>FIGURE 1 Lab air voids versus compaction temperatures for WMA (Demonstration 2).</p><p>2.3002.3102.3202.3302.3402.3502.3602.3702.3802.3902.4002.4102.4202.4302.4402.4502.4602.4702.4802.4902.500</p><p>D1HM1 D1HM2 D1WM1 D1WM2 D2WM1 D2WM2 D2HM2D2HM1Sample</p><p>Spec</p><p>ific </p><p>Gra</p><p>vity</p><p>4.0</p><p>4.2</p><p>4.4</p><p>4.6</p><p>4.8</p><p>5.0</p><p>5.2</p><p>5.4</p><p>5.6</p><p>5.8</p><p>6.0</p><p>Asp</p><p>halt </p><p>Cont</p><p>ent D</p><p>WA </p><p>(%)</p><p>Avg GMB Marshall</p><p>Avg GMB Hveem</p><p>GM...</p></li></ul>

Recommended

View more >