| Traditional asphalt concrete has been difficult to accommodate to the rapidly development trend of China's highway transportation industry.Because of its excellent high temperature performance,superior storage stability,and outstanding road performance,rock asphalt(RA)modified asphalt has gained increasingly both of scholars at home and abroad.However,it has poor low temperature performance.Adding other modifiers to RA modified asphalt can obtain RA composite modified asphalt with better performance.At present,the research on the road performance of RA composite modified asphalt has achieved some significant results,but the research on anti-aging properties and rheological properties is relatively lacking.In order to improve the rheological properties of RA modified asphalt and it can be better employed in practical engineering,the crumb rubber/rock asphalt composite modified asphalt(CR/RACMA)and SBS/rock asphalt composite modified asphalt(SBS/RACMA)were produced with different contents of crumb rubber,SBS and rock asphalt,respectively.This paper further researches on the aging characteristics and mechanism of RA composite modified asphalt.(1)The test initially formulated 10 sets of blending ratio schemes,in which the mass fraction of SBS was 2%,the mass fraction of rock asphalt was 5%,10%,12%,and the mass fraction of crumb rubber was 14%and 18%.The modifier blending scheme was first screened by penetration,softening point,viscosity test and PG test.The obtained blending ratios of the four groups were 2%SBS/5%rock asphalt,14%crumb rubber/10%rock asphalt,14%crumb rubber/12%rock asphalt,18%crumb rubber 5%rock asphalt.In the rheological test analysis,12%rock asphalt modified asphalt and 2%SBS modified asphalt were selected for comparative study.(2)For the above six sets of asphalt samples,the rolling thin film oven test(RTFOT)and pressure aging vessel(PAV)asphalt were used to study the variation of rheological characteristics.Then analyze the aging mechanism of the modified asphalt.(3)The high temperature rheological properties of six asphalt samples before and after aging were measured by dynamic shear rheometer(DSR),and the low temperature rheological properties were evaluated by bending beam rheometer(BBR).It is found that increasing the mass fraction of rock asphalt can improve the high temperature anti-rutting ability of the asphalt.Adding crumb rubber can improve the high temperature performance and low temperature performance of rock asphalt modified asphalt more effectively than SBS.The RA composite modified asphalt with 12%rock asphalt and 14%crumb rubber has the best high temperature performance,and the low temperature performance is best when the crumb rubber content is 18%.In terms of anti-aging ability,the addition of crumb rubber and SBS can improve the high temperature performance of rock asphalt composite modified asphalt after short-term and long-term aging.Compared with SBS/RACMA,CR/RACMA has low temperature performance after short-term and long-term aging.The improvement is more obvious,and the stiffness modulus increases less after long-term aging.With the increase of rock asphalt content,the high temperature deformation resistance of the rock asphalt modified asphalt undergoes aging,and its low temperature performance decline.(4)The black curve of aging of six sets of asphalt samples was obtained by the frequency sweep test(DSR).The analysis shows that SBS/RACMA has more obvious time-temperature dependence,while CR/RACMA is not applicable to the principle of time-temperature equivalence.CR/RACMA has a higher elastic component than SBS/RACMA,and the composite modified asphalt with 18%crumb rubber and 5%rock asphalt has the most elastic component.In terms of anti-aging ability,SBS can improve the viscoelastic properties of rock asphalt composite modified asphalt before and after short-term and long-term aging.(5)The multi-stress creep recovery test was used to evaluate the resistance to permanent deformation of six modified asphalt samples after short-term aging.The results show that the irreversible creep compliance Jnr3.2 can more accurately evaluate the anti-permanent deformation ability of rock asphalt composite modified asphalt compared with high temperature PG classification.CR/RACMA has a smaller unrecoverable strain than SBS/RACMA,with the addition of 18%crumb rubber and 5%rock asphalt and the addition of 14%crumb rubber and 12%rock asphalt exhibit superior resistance to permanent deformation.Compared with SBS/RACMA,CR/RACMA has better resistance to permanent deformation after long-term aging.(6)The modification effect and modification mechanism of six modified asphalt samples were tested by fluorescence scanning test.The results show that the modification mechanism of SBS/rock asphalt composite modified asphalt is physical blending,crumb rubber/rock asphalt composite modification.In addition to physical blending of asphalt,a weak chemical reaction takes place inside the crumb rubber.The aging test mechanism of the two groups of rock asphalt composite modified asphalt samples(2%SBS/5%RA and 18%crumb rubber/5%RA)after short-term aging and long-term aging was investigated.During the aging process,SBS is degraded by oxidation reaction,the crumb rubber is desulfurized and degraded,and the rock asphalt is hardened due to the decrease of light components. |
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