Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures (2016) / Chapter Skim
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43 Specific asphalt availability factors were reported by eight agencies: • 0.85 for RAS asphalt (four agencies)
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44 Survey Question: For the purposes of mix designs, indicate which "philosophy" is used to establish the contribution of the recycled material asphalt. Materials 100% Available for Mix 0% ("Black Rock")
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45 are tested and if RAP and RAS are combined prior to determining the asphalt content. A second question was included to determine which sieve size(s)
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46 determine a correction factor (four agencies for RAP, two for RAS)
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47 Not only do agencies use a range of methods for asphalt recovery, they also evaluate a range of different recycled material asphalt properties (Table 32)
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48 determine RAP gradations (15 agencies after ignition oven and nine after solvent extraction)
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49 Additional respondent comments noted that one agency conducts source tests when investigating polish resistance quality of the aggregate. Another agency noted that the contractor has the option to conduct these tests.
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50 • Contractor may choose any of these approaches. Most of the time, the contractor selects the RAP percentage and then determines the virgin binder grade they have to use.
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51 Some agencies directly measure specific gravities after ignition oven and only a few agencies measure this property after solvent extraction. The solvent extraction or the ignition oven are known to influence aggregate property test results, but are the only methods currently available for removing asphalt if an agency wants to obtain measurements, rather than estimates, of the recycled material specific gravities.
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52 SAMPLE PREPARATION The steps for the preparation of materials for fabricating mix design samples are: • Sizing of aggregates and recycled materials, • Drying recycled materials prior to batching samples, • Heating (time and temperature) of materials for mixing, • Order of addition to mixing bowl, • Short-term aging before compaction, and • Compaction of samples.
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53 • One agency noted they use 19 mm (¾ in.) as a maximum size because we ask that RAP be screened on a 25-mm (1-in.)
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54 agency reported using from 125°F to 175°F (52°C to 80°C) for a maximum of 2 hours.
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55 time in the oven to confirm the mixing temperature is reached (Table 48)
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56 AASHTO Region Statistics Aggregates RAP RAS Combination RAP and RAS Heating Time, hours Northeastern Average 3.7 1.4 1.2 1.0 Std.
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FIGURE 25 Statistics for times and temperatures used for mixing. Survey Question: Indicate how you know the material is at required temperature for mixing.
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58 Survey Question: Indicate how long materials are mixed (mixing time)
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59 Survey Question: Enter the typical number of gyration(s) , NDesign, which is (are)
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60 Sample Preparation -- Section Summary Sizing of Aggregates and Recycled Materials • If the contractors submit RAP samples from fractionated stockpiles, a number of agencies appear to use what is submitted as individual fractions for batching. • Definitions of coarse and fine RAP fractions vary.
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61 The dust-to-asphalt ratio, air voids, and VMA criteria are more difficult to meet when there is more than 25% RAP, RAS, and a combination of RAP and RAS in the mixtures. Lower percentages of RAP can make it difficult to meet these requirements, but not as frequently.
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62 At this time, only three agencies investigate trafficrelated cracking of mixtures in their state (Table 57)
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63 • Mixture stiffness is evaluated using either resilient modulus or dynamic modulus, primarily for research purposes. • Cracking potential is evaluated primarily for research purposes at this time using one or more methods (DCT and SCB at low temperatures, SCB at intermediate temperatures)
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64 • Virtually all of our agency mixtures employ a liquid antistripping agent with some hydrated lime used as well. • Using the proper asphalt binder and/or other additives can counteract the negative effects of increased RAP percentages.
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65 Survey Question: Cracking Potential (Nonthermal Cracking) : Based on your experience, indicate your level of agreement with the following statements.
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