Research On The Aging Characteristics Of Asphalt And The Influence Of Regeneration And Fusion In A Humid And Hot Environment

Under the influence of various environmental factors,asphalt pavement will undergo oxidative aging reactions,increase the content of internal polar components,produce aggregation effects of asphaltene,and damage the colloidal stable structure,resulting in performance degradation and affecting the durability of the pavement.The factors affecting aging are usually ultraviolet light,water,and temperature.However,research has shown that ultraviolet light only affects the surface layer of asphalt pavement within a range of 1cm,and the aging effect on the entire asphalt pavement is very small.At the same time,many engineering examples have shown that water vapor is also an important cause of aging damage to asphalt pavement during service,especially in dense graded asphalt pavement,where water in the body is difficult to completely eliminate,The evaporation process takes a long time,and the asphalt concrete pavement is in a long-term high humidity state during use.Therefore,in this paper,asphalt films with a film thickness of 750 μm were made by using a coater to consider the change law of asphalt wet heat aging under the action of three factors: temperature,humidity and aging time.Infrared spectrum,gel permeation chromatography and nuclear magnetic resonance hydrogen spectrum were used to test the base asphalt and SBS modified asphalt,in order to study the changes of functional groups,molecular weight distribution and internal chemical structure of the two kinds of asphalt before and after hydrothermal aging.The research results indicate that after thermal oxygen aging of asphalt,oxygen-containing functional groups such as carbonyl and sulfoxide groups increase,butadiene index decreases,and the content of internal polar components increases.Increasing humidity promotes the formation of hydrogen bonds between polar groups and water molecules,resulting in more oxygen-containing functional groups.This accelerates the aging of asphalt,but does not contribute significantly to the aging effect using liquid water.The growth rate of oxygen-containing functional groups is relatively small.The results of gel permeation chromatography show that the molecular weight distribution curve of asphalt after thermal oxidative aging moves towards the macromolecular direction,and the weight average,number average molecular weight and the proportion of macromolecules have increased.The increase of humidity and temperature can promote the asphalt to produce more macromolecular structures.For SBS modified asphalt,the proportion of macromolecules shows a trend of first decreasing and then increasing.In addition,after thermal oxidative aging,the hydrogen on the aromatic ring of asphalt will undergo substitution reaction,resulting in structural dissimilation.The content of hydrogen atoms in the fat side chain will increase,and the intermolecular force will increase.The increase of temperature and humidity can promote the degree of condensation and dehydrogenation of asphalt.Four macroscopic methods,namely frequency scanning test(TTS),multiple stress creep recovery test(MSCR),linear amplitude scanning test(LAS),and contact angle test,were used to study the changes in the viscoelastic properties,high-temperature properties,medium temperature fatigue resistance,and bonding properties of two types of asphalt before and after hydrothermal aging.The TTS test results showed that the strength of both types of asphalt increased with the increase of aging time,temperature,and humidity.The phase angle main curve of the matrix asphalt showed a monotonic decreasing trend,with an increase in elastic component and a decrease in viscous component.The phase angle main curve of SBS modified asphalt showed an S-shaped shape at the original and short-term aging states,with a turning point of 30 days.The elastic component first decreased and then increased,and then the phase angle main curve gradually tended to the matrix asphalt.The MSCR test results indicate that with the increase of aging time,temperature,and humidity,the polar components of the matrix asphalt increase,the elasticity increases,and the high-temperature rutting resistance performance improves.The high-temperature performance of SBS modified asphalt decreases 30 days before wet thermal aging and increases after 30 days,which is consistent with the variation pattern of TTS.The LAS test results indicate that with the increase of aging time,temperature,and humidity,the damage resistance and fatigue life of both asphalt types decrease.The contact angle test results show that with the increase of aging time,temperature,and humidity,the surface energy and adhesion work of the two types of asphalt decrease,the adhesion performance between the two types of asphalt and the aggregate decreases,the peeling work increases,and the resistance to water damage decreases.The impact of wet heat aging on the macro and micro properties of SBS modified asphalt indicates that the SBS modified asphalt in this article takes 30 days of wet heat aging as the turning point,with SBS modifier leading the aging process in the early stage and matrix phase leading the aging process in the later stage.Finally,the asphalt obtained after 90 days of wet heat aging under different conditions is used as the old asphalt,which is hot mixed with new asphalt and limestone.The obtained new and old asphalt recycled materials are subjected to layered peeling tests.The sulfoxide index of each layer of peeling sample is tested based on infrared spectroscopy test to quantitatively analyze the impact of different wet heat aging degrees,fusion temperatures,and asphalt types of old asphalt on the fusion degree of new and old asphalt.The results show that an increase in mixing temperature can increase the degree of fusion between new and old asphalt,and a deepening of aging of old asphalt will inhibit the fusion of new and old asphalt.The fusion degree of SBS modified asphalt is lower than that of base asphalt.