Effect Of Composition,Particle Size And Crystal Regularity Of LDHs On Properties Of Bitumen

Bitumen is widely used in road construction due to its excellent road performance.However,it is susceptible to heat,oxygen and ultraviolet light in the process of use,resulting in deterioration of its physical and rheological properties,which seriously affects the service life of bitumen pavement.Layered double hydroxides?LDHs?belongs to the class of anionic layered materials that the layer sheets and anion between layer sheets could physically shield and chemically absorb UV light,which has been used to improve the UV aging resistance of bitumen.But the laminate metal element composition?particle size and distribution and crystal regularity of LDHs can be regulated,and these factors have a certain influence on the UV reflection and absorption capacity of LDHs.Therefore,it is of great significance to research the influence of laminate metal element composition,particle size and crystal regularity of LDHs on the performance of bitumen in order to further improve the UV aging performance of LDHs modified bitumen.In this paper,LDHs with different laminate metal element composition and particle size was selected,and LDHs with different crystal regularity was obtained by roasting reduction and nitric acid treatment.They were characterized by X-ray diffraction?XRD?,field emission scanning electron microscope?FE-SEM?,laser particle size analyzer,X-ray photoelectron spectroscopy?XPS?,transmission electron microscope?TEM?and Zeta potential analyzer.Moreover,visible spectrophotometer?UV-vis?was used to analyze the UV reflection and absorption capacity of LDHs.Then,LDHs modified bitumen was prepared by melt blending.And the effects of LDHs with different laminate metal element composition,particle size and crystal regularity on physical properties,rheological properties and UV aging resistance of bitumen were investigated by properties test and fourier transform infrared?FTIR?.The main conclusions were as follows:?1?For Mg₆Al₃Zn₂-LDHs?Mg₃Al-LDHs and Mg₂Al-LDHs.UV-vis results showed that Mg₆Al₃Zn₂-LDHs have the strongest reflection and absorption ability to ultraviolet light,which is attributed to the fact that the Zn element introduced by the main laminates that reduces the band gap of LDHs and enhances their UV absorption capacity.Physical and rheological properties tests showed that Mg₆Al₃Zn₂-LDHs can significantly inhibit the deterioration of the physical properties and rheological properties of the bitumen caused by aging,and improving bitumen resistance to ultraviolet aging.?2?The results of SEM showed that the size of three kinds of Mg₂Al-LDHs were 75nm,115nm and 180nm,respectively,and theUV-vis showed that the LDHs with particle size of 180nm have the best UV reflectance.The performance test before and after UV aging showed that,compared with LDHs modified bitumen with particle sizes of 75nm and 115nm,the Mg₂Al-LDHs with particle size of 180nm has better effect on improving the physical and rheological properties of bitumen after aging,and improves the UV aging resistance of bitumen.?3?For Mg₂Al-LDHs of different crystal regularity obtained by calcination regeration and nitric acid etching,The results of SEM showed that the layered structure of LDHs after calcining disappeared and particles reunite,while the LDHs after calcination regeration recover the layered structure,but the edges are warped.TEM results showed that the LDHs after nitric acid etching have an irregular lattice arrangement within a small range,resulting in lattice defect.The results of XPS and Zeta potential test showed that the number of hydroxyl groups of LDHs after nitric acid etching decreased and the Zeta potential increased.Moreover,the UV-vis results showed that compared with the original LDHs,the reflectivity of the LDHs after calcination regeration to ultraviolet became worse,while the UV absorptive capacity of LDHs treated by nitric acid etchin was significantly improved.The performance test of bitumen before and after UV aging showed that among the LDHs modified bitumen with different crystal regularity,the LDHs after nitric acid etching has the least influence on the physical properties before aging and the best to improve the physical and rheological properties of the bitumen after aging.?4?FTIR results showed that the carbonyl and sulfoxide index of the pristine bitumen increased by 8.8 and 1.2 times respectively before and after the UV aging,while among three kinds of laminate metal element composition of LDHs,the carbonyl and sulfoxide index of Mg₆Al₃Zn₂-LDHs modified bitumen increased slowly after UV aging,only for 5.4 and 0.4 times,and had excellent UV aging resistance.Compared with LDHs with particle size of 75 nm and 115 nm,the addition of LDHs with particle size of 180 nm make the degree of increase of carbonyl and sulfoxide groups of bitumen significantly decreased after UV aging,obviously improve the UV aging resistance of bitumen.The change of carbonyl and sulfoxide index of LDHs modified bitumen with different crystal regularity can be found that the increasing degree of LDHs modified bitumen after nitric acid etching was the least,and the UV aging resistance was obviously improved.This is consistent with the influence of LDHs with different laminate metal element composition,particle size and crystal regularity on the UV aging resistance of bitumen.