The National Academies Press

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From page 174... ... 174 Evaluating the Activation of Asphalt Binder from Recycled Asphalt Shingles in Asphalt Concrete Abstract The use of recycled asphalt shingles (RAS) to replace a portion of the virgin asphalt binder in asphalt mixtures has been increasing over the past several years because of environmental and economic motivations. Read the entire page →
From page 175... ... 175 to nearly 2.0 million tons in the United States (Hansen and Copeland 2015) Read the entire page →
From page 176... ... 176 used for these mixtures was a PG 67-22, and the optimum binder content was determined at a mixing temperature of 325°F and a compaction temperature of 300°F. Activation of 100% was assumed when designing the mixtures with shingle asphalt. Read the entire page →
From page 177... ... 177 sections describe three experiments conducted to address these questions. Experiment 1: Dry Mixing with RAS The first experiment examined activation by mixing aggregate and RAS without any additional asphalt. Read the entire page →
From page 178... ... 178 250°F to 350°F. The laboratory-prepared mixtures were short-term aged for mechanical property testing for 4 h, according to AASHTO R 30-02: Mixture Conditioning of Hot Mix Asphalt (HMA) Read the entire page →
From page 179... ... 179 the mid-range temperatures, and more complete activation at the highest temperature. However, NCHRP Project 9-39 also studied the effect of temperature on compaction results and concluded that temperature had a highly significant effect on the compaction (%Gmm) Read the entire page →
From page 180... ... 180 voids for 4.75-mm NMAS designs because of their low permeability. The ignition method (AASHTO T 308) Read the entire page →
From page 181... ... 181 the Virgin Mixture, Mixture 5A (RAS aggregate and fibers only) , and Mixture 5S 300°F were not statistically different at any temperature or loading frequency. Read the entire page →
From page 182... ... 182 Group 2. Analysis of the results for this group shows that increasing the mixing temperature significantly increases the E* Read the entire page →
From page 183... ... 183 mixture except at the highest test temperature. These are important comparisons for relating the laboratory performance testing results to the field performance on Lee County Road 159. Read the entire page →
From page 184... ... 184 The hypothesis that the shingle fine aggregates and fibers would increase the cracking resistance could not be verified because Mixture 5A was not significantly different from the Virgin Mixture. Although the shingle asphalt in Mixture 5S 300°F and Mixture 5S 250°F may not have activated or blended enough to affect the cracking resistance of the mixtures, they were not adversely affected by a lack of effective asphalt. Read the entire page →
From page 185... ... 185 than the Virgin Mixture, which also supports the hypothesis that the activation of RAS asphalt reduces a mixture's cracking resistance. Indirect Tension Testing Creep compliance testing was performed at four temperatures: −20°C, −10°C, 0°C, and 10°C. Read the entire page →
From page 186... ... 186 Figure C-8 shows little differences in the compliance values among Group 1 at the two lower temperatures. At the highest test temperature (+10°C) Read the entire page →
From page 187... ... 187 thermal stress curves may have been caused by increased activation and blending of the shingle asphalt. Yet, there may be other factors affecting the shift because Mixture 5A had a higher critical temperature than the virgin mixtures. Read the entire page →
From page 188... ... 188 data from Group 2 showed a decreasing trend of DCSEf with increasing mixing temperature, and Mixture 5S PMLC had the lowest DCSEf. This indicates increased brittleness with higher mixing temperature, which may be caused by increased activation and blending of the shingle asphalt or because of additional aging caused by the higher temperatures. Read the entire page →
From page 189... ... 189 the 5% RAS thinlay has performed well with less cracking than the pretreatment cracking in the inbound direction but an increased amount of cracking in the outbound direction, although the moderate amount of cracking that now exists in the heavily loaded outbound direction after 5 years is considered to be good performance. Overall, the virgin thinlay section is clearly performing the best with the 5% RAS and 50% RAP sections performing similarly, which is consistent with OT results, creep compliance rate, and dissipated creep strain energy at failure but not consistent with energy ratio. Read the entire page →
From page 190... ... 190 brittleness of mixtures containing RAS, making them more susceptible to cracking. The hypothesis that higher mixing temperatures increase the activation of RAS binder was partially supported by statistically significant differences in the results of the performance tests for the mixes prepared at different temperatures. Read the entire page →

From page 174...

... 174 Evaluating the Activation of Asphalt Binder from Recycled Asphalt Shingles in Asphalt Concrete Abstract The use of recycled asphalt shingles (RAS) to replace a portion of the virgin asphalt binder in asphalt mixtures has been increasing over the past several years because of environmental and economic motivations.