Multiscale Research On High-Temperature Creep Behaviour Of Asphalt Mixture

The high-temperature creep behaviour of asphalt mixture makes a great impact on the appearance and development of rutting disease in asphalt pavement.Recently,most of the high-temperature behaviour researches still focus on the scales of asphalt binder and mixture.The medium scales of asphalt materials and their relationships are ignored generally.For the asphalt pavement maintenance and evaluation,it is difficult to accurately estimate the ageing degree and viscoelastic response of asphalt binder in the existing asphalt mixture.The medium scales materials including asphalt mortar and asphalt mastic provide new perspectives.To better investigate the high-temperature creep behaviours of different scales of asphalt materials and their relationships,the asphalt mixture is classified into four scales objects,including asphalt binder,mastic,mortar,and mixture.Multiple stress creep recovery（MSCR）test was selected to evaluate the viscoelastic behaviours of asphalt binder,mastic and mortar respectively.Multi-sequenced repeated loading（MSRL）test was used to estimate the high-temperature creep performance of the asphalt mixture.The relationship of asphalt binder and mortar can be built.A prediction model of asphalt mixture by asphalt mortar property was established.Then the effective relationships between different scales of asphalt mixture can be connected.Firstly,the viscoelastic behaviour of asphalt binder,mastic and mortar were evaluated by the MSCR test.To avoid the damage of the specimens,their effective ranges of loading stress were determined,and the loading stress of asphalt mortar should not be less 1.2 k Pa.The final values of J_nr and%R were determined by the average values of the last nine of ten cycles of J_nr（N）and%R（N）.Therefore,the calculation methods of J_nr and%R were modified.Based on the stress sensitivity of J_nr and%R,linear viscoelastic stress regions of asphalt binder,mastic and mortar in the MSCR test were determined respectively.It was shown that the stress region gradually increased with the increase of asphalt material scales.Secondly,the high-temperature viscoelasticity responses of asphalt binder,asphalt mastic and asphalt mortar were discussed based on their MSCR test results.The high-temperature behaviour of asphalt binder can be well evaluated by J_nr and%R.The viscoelastic performance of ageing asphalt binder can be also effectively measured.After ageing,the stiffness of asphalt binder was increased and recovery property was decreased.For the asphalt mastic MSCR test,the 1.0 mm parallel plate gap was applicable for the asphalt mastic.Based on the J_nr results of asphalt binder and mastic,a new index of filler stiffening in asphalt mastic was proposed.The appropriate filler content of modified asphalt mastic can be determined,and they were 100%-120%.For the viscoelastic behaviour of asphalt mortar,the J_nr and%R results were discussed by five main factors including fine aggregate gradations,asphalt binder types,aggregate mineral types,test temperature and ageing asphalt mortar,respectively.Based on multi-factor ANOVA results,fine aggregate gradations,asphalt binder types and stress level showed more significant influence on the viscoelastic performance of asphalt mortar.Thirdly,MSRL test was used to evaluate the high-temperature creep performance of asphalt mixture.It was shown that the high-temperature performance of asphalt mixture gradually decreased with an increase of stresses.It was similar to the stress sensitivity of asphalt binder,mastic and mortar in MSCR tests.Based on the ANOVA results of CASR values of asphalt mixture,the PG grading of asphalt binder showed a more significant effect on the high-temperature performance of asphalt mixture.An increase in asphalt binder by one PG grading,the CASR value decreased by 10-60%,and the effect was more significant for continuous gradation asphalt mixture.The skeleton structure of aggregates presented a larger effect on discontinuous gradation asphalt mixture.The correlation analysis of asphalt mixture with asphalt mortar and asphalt mastic was conducted respectively.The results showed that the behaviour of asphalt mortar presented better correlation with asphalt mixture.It was conducted that MSCR results of asphalt mortar at 12.8 k Pa was more similar to its viscoelasticity in asphalt mixture.Finally,based on the MSCR test results of asphalt binder and mortar,considering the influence of filler content and specific surface area of fine aggregates,a correlation of asphalt binder and mortar on high-temperature viscoelasticities was built.To some extent,the extraction and recovery test of asphalt binder can be avoided.On the other hand,based on the viscoelastic results of asphalt mortar and properties of coarse aggregates,a model of predicting the high-temperature performance of asphalt mixtures was established.The model adopted the high-temperature viscoelasticities of asphalt mortar(J_nr,%R and voids filled with FAM（VFF）)and coarse aggregate properties（voids in coarse aggregate（VCA））to effectively predict the high-temperature performance of asphalt mixture.Based on the performance of asphalt mortar,an effective relationship between different scales in the asphalt mixture can be better connected.