Research On Hot In-Place Recycling Technology For Modified Asphalt Pavement

As a recycling technology, hot in-place recycling (HIR) has good effect on functionality disease treatment of asphalt pavement and has been widely used in pavement maintenance in China in recent years. However, several problems are founded when this technology is applied in modified asphalt pavement. One of the problems is that the common rejuvenators are not suitable for SBS modified asphalt, and another problem is the compaction property of recycled mixture is insufficient in the field, and the third problem is the RAP content is too high in HIR so that the long term performance of HIR pavement cannot be guaranteed. The main purpose of this paper is to research on the key technologies to resolve these problems and to promote the improvement of HIR technology applied to modified pavement.The characteristics of RAP were studied based on the evaluation of asphalt mortar which are consists of bitumen, filler and fine aggregate. The RAP were collected from the upper layer of highway pavement and contained SBS modified asphalt binder. Asphalt mortars and mixtures with five RAP contents,0%,30%,50%,85% and 100%, were designed after the characteristics of asphalt binder, aggregates and aggregate gradation of RAP were tested. Based on the dynamic rheological and static creep test methods, frequency sweep test, repeated creep test, time sweep test and beam bending rheological test were employed to test the properties of asphalt mortars. And the properties of asphalt mixtures were also tested. Test results indicate that with the increase of RAP content, the asphalt mortar and mixture show very similar variations of performance, behaving as the complex modulus increase with the viscoelasticity reduce, and the rutting resistance improves while the low-temperature and fatigue properties decline. And also, the results indicate high correlation between the asphalt mortar and mixture with respect to high-temperature, low-temperature and fatigue properties, and correlation equations were built between the property indexes. Rheological parameter R, viscosity of creep stiffness Gv, cumulative dissipated energy, BBR creep stiffness and m-value were proved that could suitable evaluate the influence of RAP on the rheological and pavement properties of asphalt mortar. The cumulative dissipated energy could be used to quantitative analyze the fatigue property variation of asphalt mortar with the increase of RAP content.SBR latex is selected from the bitumen modifiers to improve the properties of recycled mixture. Infrared Spectrum Analysis results show that SBR latex could effectively supply the butadiene group for the aged asphalt, and enhance the absorption peak strength of the groups. Performance test results indicate that with the adding of SBR latex, aged asphalt and asphalt mortar’s high-temperature complex modulus increase and low-temperature complex modulus decrease, and rheological property, rutting resistance, fatigue and low-temperature properties are all improved. SBR latex could also make the recycled mixture’s high-temperature dynamic modulus and rutting factor increase, low-temperature dynamic modulus, phase angle, and fatigue loss decrease.In order to improve the compaction quality of HIR pavement, Evotherm warm mix asphalt (WMA) additive is selected to enhance the workability of recycled mixture by supplying water film lubrication, at the same time, rejuvenator with small additive amount is adopted to reduce the viscosity of aged binder. Compaction property tests were conducted using Marshall, gyratory and wheel-grind methods. Test results show that with the adding of Evotherm WMA additive and rejuvenator, compacted density of recycled mixture increase, and gyratory compaction workability energy index increase while the compaction densification index decrease, indicating that the workability and compaction property of recycled mixture have been improved.The long-term performance of recycled mixture with SBR latex and Evotherm WAM additive was tested by freezing and thawing cycles and long term oven aging methods. Test results indicate that the rutting resistance of recycled mixture improves under the influence of long term aging, but low-temperature property and moisture susceptibilities decline. And all of the three properties of recycled mixture decline after subjecting to freezing and thawing cycles. Comparing with HMA with virgin materials, recycled mixture shows lower long-term performance by the effect of freezing and thawing, but higher long-term performance under the influence of long term aging.