Study On The Structure And Properties Of Asphalt Modified With High Content Of Elastomer

Impacted by the increases of traffic load,severe environmental factors and delayed maintenance,asphalt pavement is facing severe challenges in the quality and life of service.It is important to develop high performance,low cost and easy to process modified asphalt to meet this challenge.In general,modified asphalt modified by 3%to5%wt styrene butadiene styrene block copolymer?SBS?is used in high-level asphalt pavement.For high-content SBS modified asphalt?6%wt SBS?,SBS can form a continuous phase,results in a major improvement in Bonding performance.High-content SBS modified asphalt can be used for high performance pavements exposed to high strains,such as:in bridges,thin wearing courses of highways and porous asphalt pavements.However,high cost,poor incompatible and aging resistance limits its wide use.These apprehensions can be solved to look for other economical ways for asphalt modification with high polymer concentrations.Increasing crumb rubber?CR?from discarded tires can be used as an alternative to improve roadway performance as an elastic binder additive.Beside this,the cross-linked network present in CR limits its uniform dispersion in asphalt.The aim of this work is at the basis of evaluating the structural change and aging mechanism of high-content SBS modified asphalt(HiMA_SBS)in porous pavement to adjust the degree of degradation of CR,to study the relationship between the structure and the properties of SBS/CR compound modified asphalt with rubber with different degrees of degradation and to prepare high cost-effective high-content elastomer modified asphalt.In the beginning,the indoor and outdoor aging of high-content SBS modified asphalt(HiMA_SBS,>6.0%styrene butadiene styrene copolymer,is examined to establish a relation between indoor aging and outdoor aging of porous asphalt?PA?pavement.The field core samples were taken from sections of the Shanghai Highway which had aged 6 years or 9 years outdoors and were cut into different layers?top,middle and bottom?of the PA,from which high-content SBS modified asphalt cement is separated.The recovered HiMA_SBS from different layers?top,middle and bottom?of the PA were evaluated by chemical,rheological and structural characterization like Fourier Transform Infrared Spectroscopy?FTIR?,Gel Permeation Chromatography?GPC?,Polarized Optical Microscopy?POM?,Scanning Electron Microscopy?SEM?,Dynamic Shear Rheometer?DSR?.The results show that after experiencing outdoors aging,the carbonyl and sulfoxide content of the HiMA_SBS had increased and the molecular weight of HiMA_SBS had decreased for the top layers and less change for the bottom layers,demonstrating that the top part of the PA have aged more.Rheological characterization revealed that the HiMA_SBS continue to perform well even after 6 years and 9 years of outdoor aging while the low temperature brittleness has been increased.Secondly,the relationship between the structure and the properties of SBS/CR compound modified asphalt with rubber with different degrees of degradation is studied.CR was reclaimed using a twin screw extruder and the degree of degradation is adjusted by processing temperature,to improve its dispersion properties in HiMA_SBS.The effect of content and type of highly reclaimed rubber?HRR?,reclaim degree and vulcanization on morphologies,physical properties,aging behavior and vulcanization behavior of SBS modified asphalt were investigated.These microstructure shows that the rubber powder can be dispersed in micro scale in the asphalt after the extrusion of the screw.With the increase of the extrusion temperature of the screw,the dispersion of the rubber powder in the asphalt is better,and it is better dissolved in the asphalt,and the asphalt ductility increased,heat resistance and UV aging resistance are better.Conventional performance tests show that the uniformity of high reclaimed rubber HRR/SBS composite modified asphalt(HiMA_HRR/SBS)increases with the degree of HRR degradation.Addition of HRR in HiMA_SBS showed better physical properties before and after short term aging and UV aging.In addition,the addition of sulfur further increases the ductility and aging resistance,while the processing viscosity of HiMA_SBSBS does not increase significantly.Moreover,the interaction within SBS,HRR and asphalt was studied.Dynamic Mechanical Analysis?DMA?,Thermogravimetric Analysis?TGA?and Differential Scanning Calorimetry?DSC?were used to characterize the structure and properties of HiMA_HRR/SBS modified asphalt and study deeply the interactions within HiMA_HRR/SBS,asphalt and SBS.This study specifies that the modification of the asphalt occurs via the exchange of materials among these three components.Finally,the HiMA_HRR/SBS was scaled up and pilot tested.The degraded rubber powder is compounded with SBS and dynamically vulcanized to produce modified asphalt,which is used to prepare hot mix asphalt mixture to evaluate road performance,and is applied to the third section of Huangyan Expressway pavement.The results show that HiMA_HRR/SBS has the characteristics of high softening point,good aging resistance and good thermal stability.The dynamic viscosity of HiMA_HRR/SBS modified asphalt at60°C is 12×10⁴ Pa.s,indicating that it has excellent high temperature performance.The performance of the mixture is comparable to the high content of SBS modified asphalt,which is much better than the conventional SBS modified asphalt.Brookfield viscosity is much larger than that of the conventional SBS modified asphalt,and the temperature of each working procedure is close to that of the SBS modified asphalt.HiMA_HRR/SBSRR/SBS with high cost-effective performance show a potential usage in the future.Overall,on the basis of making clear about the aging behavior of high-content SBS modified asphalt,in the thesis,high content elastomer HiMA_HRR/SBS modified asphalt is prepared,which has good high and low performance,by adjusting the degradation degree of CR.The high content elastomer HiMA_HRR/SBS modified asphalt have been scaled up and produced high-performance asphalt mixture,which is applied to high-grade road test,showing good construction performance,and combining its low cost and high performance,it will be promoted,applied and the road service level will be significantly improved.