Study On The Application Of Hot In-Plant Recycling With High Percentage Rap

With the highway asphalt pavement in our country stepping into the stage of maintenance, the annual milling process will produce a lot of asphalt pavement materials, which has positive effect on society and economy. From the point of conservation and environmental protection, the high content, large proportion of the old material recycling is the inevitable developing trend of pavement maintenance. But at present the percentage of RAP in hot mix recycling at home and abroad is generally low. This paper studies the application of hot in-plant recycling technology with high RAP. Through the indoor experiment study of regeneration, SBR latex and other additives to improve the performance of SBS recycling asphalt and improve the percentage of RAP, on this basis, to study the factory production technology, the mix design method, and the pavement performance evaluation of hot in-plant recycling with high RAP, so as to promote the technology of hot in-plant recycling with high RAP in the application of highway.Firstly, the paper analyzes the performance of modified asphalt aging. Different proportions of regeneration, SBR latex are added to the aged asphalt to reconcile based on the theory of aging asphalt reconcile regeneration. The penetration, ductility, softening point, viscosity and other general performance are tested and analyzed. We determine the regeneration content is 2% of the old asphalt quality, SBR latex content is 4% of the old asphalt quality. At the same time, new asphalt was added to further improve the performance of recycled asphalt, shows that only in terms of old asphalt performance recovery by the combined effects of additives and new asphalt, RAP blending ratio can reach 50%.Secondly, mixing temperature, materials adding order, mixing time of hot in-plant regeneration process were analyzed and discussed. By laboratory test we determine the optimal mixing temperature of the recycled mixtures with warm agent, reasonable RAP and new aggregate mixing temperature; at the same time, we study the influence of materials adding order, mixing time to the performance of recycled asphalt mixture, and finally determine the optimal combination of the hot in-plant production process based on gray correlation theory with the multi-index evaluation to recycled mixture's road performance.Furthermore, the recycled mixture's key control design parameters include VMA, maximum theoretical density were analyzed, focusing on the maximum theoretical density correction formula. On this basis, using Marshall design method to determine the 30%,40% and 50% RAP content of recycled asphalt mixture gradation composition, optimum asphalt content, etc., and use the Superpave design method to verify if the performance indicators can meet the design standard of new mix asphalt mixture based on the theory of Marshall design. Finally we further prove the mix design is reasonable.Finally, we had a comprehensive study of the different content of high RAP regeneration mixtures by dynamic creep test, Semi-Circular Bending test, freeze-thaw splitting test and semicircle fatigue tests, and comparing with ordinary hot mix asphalt mixture. Based on the test results, we explore adding fiber to further improve the road performance of hot in-plant recycling mixture with high RAP. Finally we realize the RAP content up to 50% of the recycled asphalt mixture satisfies the requirement of expressway, which makes hot in-plant recycling technology with high RAP application in highway construction and maintenance.