Asphalt Technology News - Auburn University

More documents

Recommendations

Info

The objective of this study was to identify the most accuratemethod for determining the RAP aggregate G sb.MethodologyFour Superpave mix designs were developed using unmodifiedbinder and four virgin aggregate sources: hard limestone fromAlabama, soft limestone from Florida, granodiorite from Californiaand rhyolite from Nevada. Aggregate properties, including G sbandabsorption, were determined for each blend. The lab-producedmixes were oven-aged for five days to create a simulated RAP.After the long-term aging process, each mix was separated intofour portions, one for determining G mm(AASHTO T 209) and onefor each of three extraction methods: centrifuge method (AASTHOT 164 Method A), reflux method (AASHTO T 164 Method B) andignition oven method (AASHTO T 308).The measured G sbvalues for the virgin and recoveredaggregate were determined in accordance with AASHTO T 84 andAASHTO T 85. The G mmmethod was also used to estimate the G sbof the RAP aggregate. This method requires the following inputs:• G mm• Asphalt content: The asphalt contents from the ignition oventest were used since its results were closest to the true asphaltcontent for each mix.• Asphalt absorption: Absorption was calculated using knownspecific gravity values. In actual practice, absorption would beestimated based on typical values from asphalt mixes in thearea where the RAP was obtained.Results and ConclusionsFor each material, the estimated G sbusing the G mmmethod wasthe most similar to the true G sb. Currently, there is no establishedcombined G sbtolerance to define acceptable differences withina laboratory. For the purposes of this research, an acceptabledifference was established for thecombined G sbbased on AASHTOtolerances for coarse and fine G sbvalues. The acceptable differenceswithin a laboratory for coarse and fineG sbare 0.025 and 0.032, respectively.The coarse and fine aggregateswere treated as individual stockpilesin the combined G sbequation, withthe individual G sbvalues being theacceptable differences. It should benoted that an acceptable differencefor the combined G sbwas calculatedfor each mix since the percentagesof fine and coarse aggregate variedbetween the mixes. The calculatedacceptable differences for combinedG sbwere used to determine if thedifferences between the four RAPG sbmethods and the true G sbwereacceptable. Based on the calculatedacceptable differences, all resultswould be considered similar to theVMA Difference (%)0.00-0.02-0.04-0.06-0.08-0.10-0.12-0.14-0.16true G sb, with the exception of the Florida limestone recoveredby the ignition oven. Table 1 summarizes the differences betweentrue G sband measured or estimated G sbfor each method.Figure 1. shows VMA errors (calculated for each source usingthe estimated G sbdetermined from the G mmmethod) as RAPpercentage increases. While the differences found betweenresults of the various methods for determining RAP aggregateG sbseem small (all were less than 0.040), these errors can have alarge impact on calculated VMA as the RAP percentage increases.When using the G mmmethod of estimating RAP aggregate G sb,the calculated VMA errors were less than 0.2 percent, which isconsidered reasonable for high RAP mixes which will be subjectedto additional performance testing during the mix design process.RecommendationsBased on these results, it is recommended that the G mmmethod be used to determine the RAP aggregate G sbwhen alocal absorption value is available. The ignition method shouldbe used for determining asphalt contents of RAP materials, exceptin regions where ignition method aggregate correction factorsare not reliable. If a local absorption value is not known, then theRAP aggregate G sbshould be measured using solvent extractedaggregate.AlabamaFloridaCaliforniaNevada0 10 20 30 40 50 60 70RAP Percentage14Asphalt Technology News
Training OpportunitiesNCAT offers a variety of training opportunities to fit your needs. To register for a class or for more information,please visit our website: www.ncat.us or call Linda Kerr at 334.844.7308 or Don Watson at 334.844.7306.ASPHALT TECHNOLOGYThe Asphalt Technology course is a one-week training programdesigned to provide a basic understanding of asphalt technologyfor technicians, engineers and employees from all sectors ofthe asphalt industry. If you are looking for a general overviewof HMA technology and how all aspects of design, production,construction and maintenance come together, then this is thecourse for you. Participants will be better able to communicateeffectively with asphalt specialists and understand customer needs.This course provides 3.2 Continuing Education Units (CEUs),equivalent to 32 Professional Development Hours, and will be heldat NCAT facilities in Auburn, Alabama.Dates: January 25-29, 2010(Registration and payment deadline: January 15, 2010)February 22-26, 2010(Registration and payment deadline: February 12, 2010)SUPERPAVE MIX DESIGNThis workshop provides a more technical understanding ofmaterials specifications, test procedures, mixture performancetests and general mix design requirements. The objective is toprovide technicians, engineers, testing personnel and inspectorswith an understanding of the development of a Superpavevolumetric mix design. Upon completion of the workshop,participants will be ableto develop a Superpavevolumetric mix design intheir laboratories. Thiscourse provides 2.8 CEUs (28Professional DevelopmentHours) and will be held atNCAT facilities in Auburn,Ala.CUSTOMIZED TRAININGNCAT can also provide customized training to meet yourindividual training needs. Workshops can be conductedat our facilities or yours, at a time convenient for you. Onsiteworkshops allow agencies and contractors to makethe most efficient use of their training budgets whilecomplying with imposed travel restrictions. Workshopscan also be tailored to fit the technical needs of yourpersonnel.For example, a one-day HMA Construction course wasrecently conducted for Russian engineers and contractorsvisiting Chattanooga, Tenn. The course covered all aspectsof HMA construction including production, placement andcompaction. Presentations covered the plant types usedin HMA production and the advantages/disadvantagesof each, paver operation and electronic controls, andthe various types of rollers. A simple software programwas used to show how plant production and roadwayoperations should be coordinated to provide a continuousoperation. Another software program was used todemonstrate how much time is available for compactionbased on site conditions. Procedures for effective qualitycontrol/quality assurance and current research were alsoreviewed.Date: March 22-25, 2010(Registration and paymentdeadline: March 12, 2010)Fall 2009 • Vol. 21 • No. 215
Page 2 and 3: Comparisons of distress measurement
Page 4 and 5: plants. TLA pellets account for 25
Page 6 and 7: is a way to relate modulus values o
Page 8 and 9: Asphalt Forum ResponsesThe followin
Page 10 and 11: RST are permitted in SMA and 1 perc
Page 12 and 13: • A range of design air voids (4
Page 16: www.ncat.eduAuburn University is an

Asphalt Technology News - Auburn University

Create successful ePaper yourself

Delete template?

Save as template?