| Petroleum asphalt has been widely used in road construction due to its excellent bonding properties.However,during the use of the pavement,the asphalt is affected by environmental factors such as heat,light,and oxygen and ages,resulting in the deterioration of its performance,thereby shortening the service life of the asphalt pavement.Asphalt is made from crude oil.Its chemical composition and molecular structure depend on the type and processing technology of crude oil,and directly affect its aging performance.At present,there have been many studies on the effect of aging on the properties of asphalt,but there are few studies on the effect of aging on the chemical composition and molecular structure of asphalt from different crude oil.Therefore,it is important to study the effects of aging on the chemical composition structure and their properties of different crude oil asphalts,and to establish the correlation between the molecular structure of asphalt and its physical properties and aging properties for the production and application of asphalt.In this paper,18 kinds of road asphalts from different crude oil were selected.The molecular weight and distribution of different asphalts were tested by gel permeation chromatography.Elemental analysis,infrared spectroscopy(FTIR),and hydrogen nuclear magnetic resonance(~1H-NMR)spectroscopy were used to determine the chemical structure of asphalt before and after short-term thermal-oxidative aging(TFOT),long-term thermal-oxidative aging(PAV)and ultraviolet light aging(UV).The physical properties of asphalt before and after aging were tested,and the anti-aging properties of asphalt were evaluated.The influence of different aging methods on the chemical composition,structure and physical properties of asphalt from different crude oil was studied.The relationship between the chemical composition and structure of asphalt and its physical properties and aging properties was established.The main conclusions are as follows:(1)There are obvious differences in the chemical composition and structure of asphalt from different crude oil.The C content of the 18 kinds of asphalts ranges from 81%to 86%,the H content ranges from 9%to 12%,the N content ranges from0.2%to 1%,the S content ranges from 0.8%to 7%,and the O content ranges from0.6%.～2.5%,hydrogen to carbon atomic ratio(H/C)is between 1.35～1.68.The molecular weight ranges from 564 to 766.The sulfoxide index is between 0.003 and0.019,the aromatic index is between 0.034 and 0.111,the aromatic carbon ratio is between 0.187 and 0.368,and the number of aromatic rings is between 1.332 and4.241.(2)Aging had a great influence on the elemental composition of different crude asphalts,as shown in the decrease of C and H element content,and the content of C decreased by 0.01%～0.77%,0.04%～1.43%and 0.01%～1.56%respectively.The content of H decreased by 0.13%～1.78%,0.35%～2.43%and 0.66%～2.70%respectively.The content of O increased by 8.37%～127.38%,56.49%～217.91%,32.22%～200.75%respectively,and the value of H/C decreased by 1.29%～13.48%,3.97%～19.49%and 7.09%～20.81%respectively.The ring structure and aromatic ring structure of asphalt increased.(3)The effects of TFOT,PAV and UV aging on the molecular structure of different crude oil asphalt were quite different.During the TFOT aging process,the aromatic ring branches of asphalt decreased,the aromatic ring structure increased,and the alkyl chain was cyclized,and the aliphatic straight chain was cleaved to generate short chains.During the PAV aging process,the carbonyl groups of asphalt increased more,especially the asphalt with smaller molecular weight and aromatic carbon ratio and larger H/C produced more carbonyl content,and was more seriously affected by aging.It was accompanied by the phenomenon of aromatization and polycondensation,and the polymerization of short aliphatic branched chains to form long chains.During the UV aging process,the degree of condensation of the asphalt increased continuously,and the long chains were broken and cyclized to produce more short chains.(4)There were obvious differences in the physical properties of asphalt with different compositions and structures after aging.The asphalt with larger molecular weight,aromatic carbon ratio and aromatic ring number and smaller h/c had smaller softening point increment and viscosity,larger residual penetration and ductility after aging,showing better anti-aging performance.However,the asphalt with smaller molecular weight,smaller aromatic carbon ratio and larger H/C ratio had larger softening point increment and viscosity after aging,and smaller residual penetration and ductility,showing poor anti-aging performance.(5)The gray correlation analysis showed that the influence of chemical composition structure on residual needle penetration and softening point increment was in the following order:carbonyl index>aromatic carbon rate>aromatic ring number>molecular weight>H/C>sulfoxide index>aromatic index;the influence of composition structure on viscosity ratio was in the following order:molecular weight>carbonyl index>aromatic ring number>sulfoxide index>H/C>aromatic carbon rate>aromatic index. |
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