## 6 Field Performance of RAS-Modified Asphalt Mixtures  
In 1993, RAS-modified dense-grade asphalt and stone mastic asphalt (SMA) mixtures were prepared using two pen-grade bitumens (85/110, 120/150) and three different RAS types (i.e., end-life roofing membrane shingles, felt-backed MWSS, and fiberglass MWSS). In the laboratory, specimens were prepared for dense-grade as well as stone mastic asphalt [33]. Then, some field experiments were performed to obtain the actual performance of the modified mixtures. According to the volumetric analysis and binder extraction, RAS decreased the quantity of the virgin binder required for the conventional mixtures. Moreover, 5% RAS did not affect the thermal cracking and moisture susceptibility of the corresponding virgin binder reference mixtures. However, the permanent deformation performance of the mixes improved [33]. In 1998, a field study related to the use of RAS in asphalt mixtures was documented by the Georgia Department of Transportation. In 1994 and 1995, [PERSON] performed tests on two sections of flexible pavement built with 5% RAS. Visual inspection showed that the RAS-modified flexible pavements performed relatively better than conventional asphalt mixtures. It was also concluded that adding RAS to an asphalt mixture renders it stiffer in comparison with traditional asphalt mixtures, improving the high-temperature performance while compromising the low-temperature performance of asphalt mixtures. Their study recommends the addition of 5% RAS in order to improve the high-temperature performance in Georgia's warm climates [61]. McGraw performed tests on RAS- and RAP-modified asphalt mixtures. In the RAS, both end-life tear-off scrap shingles (TOSS) and manufactured waste scrap shingles (MWSS) were used. All results were derived from field test sections in Minnesota (data collection started in 2008). Three test pavement sections were continuously monitored; they were modified with 5% MWSS + 15% RAP, 5% TOSS + 15% RAP, and 20% RAP, respectively. PG58-28 as a virgin binder was used in all three mixes. Putting was not a significant problem, while transverse cracking occurred in all sections, most of which occurred along curbs, gutters, and utilities (manholes, sewers, etc.). Because of this, it was impossible to attribute the damage to the presence of recycled materials only. After the first winter in service, the RAS pavement developed many reflective cracks and was relatively more brittle. The RAS pavement also had more transverse cracking than the control section, although no significant rutting was noticed in any of the pavement sections studied. According to the authors, other factors, such as \"long haul times and late-season paving\", could have contributed to the poor performance, emphasizing the necessity of maintaining the optimal compaction temperature [62]. [PERSON] et al. conducted a research study on recycled asphalt shingles in Ontario using hot-mix asphalt and concluded that 3% recycled asphalt shingles or a smaller percentage in combination with RAP could meet the design specifications. They also performed a friction test in the field (using the British Pendulum) in the wheel paths of shingle-modified trial-laid mixes and noticed an average British Pendulum number greater the 45 with only a 2.1% standard deviation, indicating very close values to the individual values [63]. [PERSON] performed a comparative study of RAP-modified bituminous mixtures and shingle-modified bituminous mixtures and found similar behavior in both mixes during placement as well as compaction. In terms of rutting, RAP mixes had borderline results, while shingle-modified mixes had satisfactory results. Moreover, bitumen extracted from both types of mixes (RAP as well as shingle-modified bituminous mixture) taken from an asphalt plant showed an increase in their performance grade from PG 64-22 to PG 70-22. An economic analysis of 5% asphalt shingle-modified bituminous mixtures in reference to neat bituminous mixtures was also performed in the cited study.