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|Title:||Evaluation of properties of recycled asphalt concrete hot mix|
|Authors:||Brown, E. R. (E. Ray)|
|Publisher:||Geotechnical Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Technical report (U.S. Army Engineer Waterways Experiment Station) ; GL-84-2.|
Abstract: Recycling of aged asphalt concrete pavements has been demonstrated to be cost-effective and to reduce the demand for natural resources such as aggregate and asphalt . Because of the advantages derived when using recycled materials, the capability to predict long-term performance is needed so that optimum benefits can he obtained. This study was undertaken to evaluate the laboratory performance of recycled asphalt concrete mixtures and to compare these results to those measured for conventional asphalt concrete mixtures. Two aggregate types, a crushed gravel and a crushed limestone, were used to produce two conventional mixtures and to blend with the reclaimed asphalt pavement to produce the six recycled mixtures. Three asphalt materials which were obtained to produce the various mixtures being evaluated consisted of AC-20 for preparing the conventional mixtures and AC-5 and a recycling agent for preparing the recycled mixtures. The first step in preparing the recycled mixtures was selecting the aggregate type that compared most favorably with the aggregate in the reclaimed asphalt pavement. Recycled mixtures were then prepared using the AC-5 in three mixtures and the recycling agent in three mixtures, resulting in eight mixtures for evaluation (six recycled and two conventional mixtures). The relative durability, low temperature, water susceptibility, and fatigue properties were evaluated for all mixtures. Tests were conducted on the asphalt binder (combined binder for recycled mixtures) prior to mixing with aggregate and after being recovered from the mixtures used to evaluate fatigue properties. These tests on the binder included penetration at 40°F and 77°F; ductility at 40°F and 77°F; soften1ng point; viscosity at 275°F, 225°F, and 140°F; specific gravity; and rolling thin-film oven test. Tests conducted on the asphalt concrete consisted of Marshall stability at 140°F, indirect tensile test at 40°F and 77°F, resilient modulus at 40°F and 77°F, flexural fatigue test at 40°F and 77°F, and water susceptibility test. The Shell BISAR computer program was used to predict the stresses and strains for two typical pavement sections under a given loading condition. Computed stresses and strains were then analyzed along with the laboratory fatigue tests to predict the fatigue performance of the various mixtures. Results of this study indicated a satisfactory comparison between laboratory performance of recycled mixtures and conventional mixtures. Fatigue analysis indicated that conventional mixtures would provide the greatest fatigue resistance in thick asphalt concrete layers at lower temperatures, while the recycled mixtures would provide the greatest fatigue resistance in thin asphalt layers at higher temperatures. Water susceptibility was shown to be related more to aggregate type than to mixture type. The data show that recycled mixtures prepared with the recycling agent produced mixtures with the lowest durability and poorest low temperature performance when compared with the recycled mixtures prepared with AC-5 or compared with the conventional mixtures.
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