Research On Composition Design And Performance Of Large Stone Porous Asphalt Mixes

With the increase of highway traffic volume, axle load, tire pressure, asphaltpavement suffers severe permanent deformation and fatigue damage during the initialstage of its usage. The inherent defects of semi-rigid base material which can result inreflection crack and water damage of asphalt pavement have also become increasinglyprominent. Large stone porous asphalt mixes (LSPM) provides an efficient way and anew idea to solve or alleviate the problems above. In China, the study of LSPM is stillrelatively weak and there is no any clear definition exists so far. Based on the researchand practice of large stone asphalt mixture and drainage asphalt mixture at home andabroad, the composition design and performance of LSPM is studied in this paper.Considering the structural layer function of the pavement where the LSPM is pavedon, the structural constituent and strength composition of LSPM are analyzed. Based onbailey method for gradation design, and a preset parameter is introduced namely“reserved air voids”, the method for LSPM gradation design is established. Thefeasibility of bailey method for designing the gradation of the void-skeleton asphaltmixture has been verified through the examination of design gradation. Considering theproportion of asphalt absorbed by aggregate, effective asphalt film thickness and specificsurface area of aggregate, a calculation method for determining initial asphalt content isproposed. On this foundation, the method for determining the optimum asphalt content ofLSPM is established, which combines some indexes such as effective asphalt filmthickness, air voids, the volume index of large scale Marshall specimen, the loss ofbinder draindown and Cantabro abrasion.The performance of LSPM is preliminarily studied through some laboratory testsincluding high temperature stability test, water stability test, permeability test and fatiguetest. The results showed that LSPM with well-designed gradation significantlyoutperformed the traditional asphalt concrete at the aspect of rutting resistance. Theresults also indicated that the water damage resistance of LSPM mainly depends on theeffective asphalt film thickness on the premise of meeting the loss of asphalt binder draindown. Furthermore, considering the balance between drainability and durability, theair voids are set from13%to18%, which can meet the draindown requirement andachieve good durability as well.The key points of field construction technology and quality control of LSPM arediscussed through in-situ test road. After over eight month’s vehicles loading, there areno obvious ruts and cracks. The results preliminary showed that overlaying on existingcement concrete slab has good ability in resisting high temperature permanentdeformation and reflective cracking. The long-term performance of the test section stillneeds further observation.