Preparation,Performance And Modification Mechanism Of Organic Intercalated LDHs Modified Bitumen

Bituminous pavement has been widely used in highway construction due to its excellent road performance.However,bitumen would be subjected to aging under the effect of ultraviolet?UV?light,heat,and oxygen,which would lead to the the shortening of service life of bituminous pavement.Therefore,improving the anti-aging performance of bitumen is of great significance to extend the service life of pavement.In recent years,layered double hydroxides?LDHs?has been applied to improve the aging resistance of bitumen due to its excellent physical shielding and chemical absorption effect to UV light.But the compatibility between LDHs and bitumen is very poor because of the hydrophilic instinct of inorganic LDHs,the LDHs particles cannot be dispersed into bitumen uniformly and are prone to separation and agglomeration during the hot storage and transport,leading to the weakened blocking and absorption effect of LDHs to UV light,and consequently the improvement effect of LDHs to UV aging resistance of bitumen is decreased obviously.To improve the compatibility between LDHs and bitumen,the organic anionic compounds were intercalate into the interlayer of LDHs based on the anion exchangeable of LDHs,achieving the organic modification of LDHs,and then the anti-aging performance of bitumen is significantly improved.In this paper,the effect of LDHs content on the properties of bitumen was firstly studied to determine the optimal dosage of LDHs.Then anion exchange method and structure reconstruction method were used to prepare organic intercalated LDHs with different guest anions in the interlayer by intercalating three organic anionic compounds,sodium dodecyl benzenesulfonate?SDBS?,sodium dodecyl sulfate?SDS?and sodium dodecyl sulfonate?SDSO?,and two anionic UV absorbents,2-hydroxybenzoic acid?HBA?and 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid?HMBSA?,into the interlayer of LDHs,and X-ray diffractometer?XRD?,fourier transform infrared?FTIR?,field emission scanning electron microscope?FE-SEM?,ultraviolet and visible spectrophotometer?UV-vis?and thermogravimetry and differential scanning calorimetry?TG–DSC?were applied to characterize organic intercalated LDHs,afterwards,organic intercalated LDHs modified bitumen was prepared by melt-blending method.The compatibility between LDHs and bitumen was studied,and the effects of organic intercalated LDHs on the physical and rheological properties,thermal-oxidative and UV aging resistance performance of bitumen were investigated.Finally,the thin layer chromatography-flame ionization detection?TLC-FID?,FTIR and XRD were used to characterize the four components,chemical structures and crystal structure of organic intercalated LDHs modified bitumen before and after aging,and based on the results,the modification mechanisms of organic intercalated LDHs on improving the aging performance of bitumen were revealed.The main conclusions were as follows:?1?The modification by LDHs increases the softening point,viscosity and complex modulus of bitumen while decreases the phase angle,thus improves the deformation resistance of bitumen at high temperature.Aging test results indicate that LDHs enhances the thermal-oxidative and UV aging resistance performance of bitumen,but with the increasing of LDHs dosage,the separation degree of LDHs modified bitumen becomes more and more severe,the compatibility between LDHs and bitumen decreases obviously.?2?The organic intercalated LDHs can be obtained by both anion exchange method and structure reconstruction method which could make the organic anions substitute the CO₃^2-in the interlayer of LDHs.The molecules of SDBS,SDS and SDSO form a monolayer guests in the interlayer space with the alkyl chains remaining in perpendicular to the LDHs layers,while HBA and HMBSA chains form a parallel bilayer with arrangement of tilted chains and overlapped benzene ring,the interlayer spacing is dependent on the length and arrangement of organic anions.?3?UV-vis spectra illustrate that organic-modified LDHs still show excellent UV shielding effect,and the anionic UV absorbents enhance the UV absorbance of LDHs significantly.Meanwhile,the thermostability of anionic UV absorbents intercalated into LDHs is strengthened remarkably under the protection of host layers.?4?The compatibility of organic intercalated LDHs prepared by ion exchange method and structure reconstruction method with bitumen is enhanced obviously,the organic intercalated LDHs could disperse in bitumen homogeneously and the separation of organic intercalated LDHs is distinctly reduced.The compatibility between organic intercalated LDHs and bitumen is related to the species of organic anions,the interaction force between organic anionic modifiers and bitumen molecular is stronger and the interlayer spacing of organic intercalated LDHs is larger,then the compatibility between organic intercalated LDHs and bitumen is better.?5?In comparison with LDHs,organic intercalated LDHs enhance the deformation resistance of bitumen at high temperature and endow bitumen with better low temperature performance,that is because the organic intercalation enhances the compatibility between LDHs and bitumen?6?OrganicintercalatedLDHsmodifiedbitumenexhibitsbetter thermal-oxidative and UV aging resistance profermance,and the better the compatibility between organic intercalated LDHs and bitumen is,the more obvious the improvement effect of organic intercalated LDHs is.In comparison with other organic anion intercalated LDHs modified bitumens,anionic UV absorbent intercalated LDHs modified bitumens show more prominent UV aging resistance.?7?LDHs with high aspect ratio could inhibit the volatilization of light component and the penetration of oxygen to bitumen,resulting in the improved thermal-oxidative aging resistance of bitumen.Nevertheless,the dispersibility of LDHs in bitumen is very poor and the LDHs is prone to agglomeration,consequently,the aforementioned inhibition effect of LDHs cannot work effectively.The organic intercalated LDHs in bitumen have good dispersing stability,which enables LDHs to display the inhibition function better,and thus enhance the thermal-oxidative aging resistance of bitumen effectively.?8?The TLC-FID,FTIR and XRD analyses reveal that organic intercalated LDHs could block the UV light and obstruct the permeation of oxygen,retarding the reaction rate of photo-oxidative aging of bitumen remarkably,then inhibit the transformation of bitumen components and the generation of polar oxygen-containing functional groups and polycyclic aromatic sheets,those effects of organic intercalated LDHs alleviate the intermolecular association of bitumen and impede the migration and stack of polycyclic aromatic sheets to the surface of asphaltenes,and then improves the UV aging resistance of bitumen.