Study On Preventive Maintenance Technology Of Porous Asphalt

The security of porous asphalt is highly recognized. Due to its skid resistance, noise reduction and driving comfort, it can decrease the accident rate in rainy days by 50% and decrease 3-8 decibels of the noise. Ravelling and potholes, the most common structural destruction forms of porous asphalt as a result of the large void and open grade, cause a severely negative effect on its longevity, comfort and safety. To avoid diseases, preventive maintenance technology of porous asphalt is studied. The benefits include diseases postponement, service life-prolonging and road performance such as skid resistance, noise reduction except carrying capacity improvement.To begin with, the main diseases of porous asphalt were analyzed. Clogging and ravelling are the main forms of functional diseases and structural diseases separately. The formation mechanism of ravelling is deeply related to the high-viscosity modified asphalt ageing which causing the cohesion failure of asphalt binder and adhesion failure of aggregates stripping. The discrete element model of porous asphalt was established by the steps of gradation-basic sphere-pre-compaction forming method. Distributing regulation of ravelling diseases of Porous asphalt were simulation analysis. The panel ravelling devices were developed, which were accurately simulative to tire-road impaction. Based on texture depth, a new evaluation method of ravelling was presented.Then, based on the mechanism of ravelling, the performance requirements of materials for preventive maintenance technology were presented. Three different types(rejuvenation, cohesiveness reinforcement and polymerization) of preventive materials (RJ, CEM and GL1) were developed, with emulsified asphalt (EA) for comparison analysis. The properties of preventive materials by apparent viscosity, cohesion and adhesion indicator with aggregates were characterized.After PAV long-term ageing, four preventive materials were added to aged high-viscosity asphalt by different contents (5%,10% and 15%) to regenerat asphalt. To discuss the reduction mechanism of the preventive materials, the microstructure of regenerated asphalt was analyzed by GPC, FT-IR and fluorescence microscope. The transforms of rheological properties by each kind of preventive materials were found out by Dynamic Shear Rheometer(DSR) and Bending Beam Rheometer (BBR). Analyses including temperature sensibility (DSR temperature scanning), high temperature creep property (multi-step creep and recovery test), dynamic shear modulus (frequency scanning), fatigue property (linear amplitude scanning) and low-temperature crack resistance (BBR low-temperature bend test). Porous asphalt mixtures were been preventive by. The anti-ravelling, permeability and skid resistance of porous asphalt mixture that had been treated by preventive maintenance materials were studied. The effect of preventive materials on the internal structure of pavement and the distribution of materials in the pavement were studied by industrial CT scanning.These three preventive materials were proved to decrease the variety of carbonyl content caused by high-viscosity modified asphalt ageing and increase aromatic base content, which improved the anti-ravelling ability of porous asphalt to some extent. RJ, the regeneration material, showed great distribution property when at the low mass content (5%), and could highly develop the rheological property of aged asphalt. It had great fluidity, uniform distribution and little impact on the void structure. The content of RJ should be under 10%. Polymeric reactive material GL1 with high viscosity and cohesion could coat aggregate well, vary the sulfoxide content of aged asphalt, decrease the molecular weight of aged asphalt distinctly, permeate more than 70% depth of the pavement, and its influence rate to permeable ability was less than 5%. CEM, the bonding enhancement material, could develop the low-temperature crack resistance of aged asphalt, controled the difference of original BPN more than -2.03 and had little impact on skid resistance.Finally, the critical technology of preventive maintenance was studied, including the optimum dosage of preventive materials, the period of opening to traffic, three construction ways of materials, effects, mechanismd and the range of application. Compared different ways of clogging cleaning, and the specific sanitizer is an optimal choice. Protection measures for crucial positions were presented. The preventive maintenance materials and construction procedure presented above were applied in a test pavement, which was observed for a whole year to evaluate the effect. Preventive materials could highly improve the anti-ravelling property and low-temperature crack resistance of the pavement. In the preliminary stage (the first three months), it had some negative impacts on the skid resistance and permeable ability, but as time passes, its effect decreased. Moreover, the occurrence of ravelling was postponed, the level of its variety trend was slowing. Eventually, the longevity of porous asphalt could be achieved.