Lihui Xue

Effect of aging on the morphology of bitumen by atomic force microscopy.

Effect of aging on the morphology of bitumen was investigated. Two bitumens were aged according to the thin film oven test (TFOT), pressure aging vessel (PAV) test and ultraviolet (UV) radiation, respectively. The morphology of the binders before and after aging was characterized by atomic force microscopy. The physical properties and chemical compositions of the binders were also measured. The results showed that aging affected the bitumen morphology significantly. Aging increased the overall surface stiffness of the bitumen and made the bitumen surface more solid‐like. The extent of these changes was dependent on aging conditions. TFOT decreased the contrast between the dispersed domains and the matrix, which contributed to the single‐phase trend of the binders. The effect of PAV aging on morphology of the binders was dependent on the base bitumen. In one case, it further accelerated the single‐phase trend of bitumen in comparison with that after TFOT. In the other case, it caused the phase separation of bitumen. In both cases, PAV aging increased the surface roughness of the binders obviously. As a result of UV aging, the contrast between the matrix phase and dispersed phase was increased due to the difference in sensitivity to UV radiation of the bitumen molecules, which caused or further promoted the phase separation in the binders. Regardless of the aging procedure carried out, a strong correlation was observed between the changes in morphology and physical properties as well as chemical compositions of the binders before and after aging.

Effect of montmorillonite organic modification on microstructures and ultraviolet aging properties of bitumen

The effect of montmorillonite (MMT) organic modification on microstructures and ultraviolet (UV) aging properties of bitumen was investigated. The microstructures of MMT modified bitumen were characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM), respectively. The binders were aged by UV radiation. The UV aging properties of MMT modified bitumen was studied by determining physical properties and AFM analysis. XRD and FTIR analyses show that the sodium montmorillonite (Na+‐MMT) modified bitumen forms a phase‐separated structure, whereas the organo‐montmorillonite (OMMT) modified bitumen forms an intercalated structure. After Na+‐MMT modification, the contrast between the matrix and the dispersed domains is inverted according to AFM analysis. However, this contrast inversion is prevented with the introduction of OMMT due to the good compatibility between the OMMT and the bitumen. As a result of UV aging, both viscosity aging index and softening point increment of OMMT modified bitumen are lower than that of the unmodified bitumen and Na+‐MMT modified bitumen. Furthermore, the association interactions and single‐phase trend in OMMT modified bitumen are further prevented in comparison with Na+‐MMT modified bitumen during UV aging, indicating the good aging resistance of OMMT modified bitumen after organic modification of MMT.

Investigation of γ-(2,3-Epoxypropoxy)propyltrimethoxy Silane Surface Modified Layered Double Hydroxides Improving UV Ageing Resistance of Asphalt

γ-(2,3-Epoxypropoxy)propyltrimethoxy silane surface modified layered double hydroxides (KH560-LDHs) were prepared and used to improve the ultraviolet ageing resistance of asphalt. The results of X-ray photoelectron spectrometry (XPS) indicated that KH560 has been successfully grafted onto the surface of LDHs. The agglomeration of LDHs particles notably reduced after KH560 surface modification according to scanning electron microscopy (SEM), which implied that the KH560 surface modification was helpful to promote the dispersibility of LDHs in asphalt. Then, the influence of KH560-LDHs and LDHs on the physical and rheological properties of asphalt before and after UV ageing was thoroughly investigated. The storage stability test showed that the difference in softening point (ΔS) of LDHs modified asphalt decreased from 0.6 °C to 0.2 °C at an LDHs content of 1% after KH560 surface modification, and the tendency became more pronounced with the increase of LDH content, indicating that KH560 surface modification could improve the stability of LDHs in asphalt. After UV ageing, the viscous modulus (G’’) of asphalt significantly reduced, and correspondingly, the elastic modulus (G’) and rutting factor (G*/sin δ) rapidly increased. Moreover, the asphaltene increased and the amount of “bee-like” structures of the asphalt decreased. Compared with LDHs, KH560-LDHs obviously restrained performance deterioration of the asphalt, and helped to relieve the variation of the chemical compositions and morphology of asphalt, which suggested that the improvement of KH560-LDHs on UV ageing resistance of asphalt was superior to LDHs.

Performance evaluation of asphalt containing layered double hydroxides with different zinc ratio in the host layer

ABSTRACT The effects of five layered double hydroxides (LDHs) with different zinc ratio on the physical and rheological properties, chemical components, and anti-UV aging performance of asphalt were evaluated. Results show that LDHs improve the deformation resistance of asphalt at high temperature. After UV aging, LDH-modified asphalts show the smaller changes of physical and rheological properties and chemical components in comparison with asphalt, indicating the improved UV aging resistance. By comparison, the LDHs with higher ratio of zinc in the layers have the more outstanding UV reflection ability, leading to a beneficial effect in improving UV aging resistance of asphalt.

Investigation of Molecular Structure and Thermal Properties of Thermo-Oxidative Aged SBS in Blends and Their Relations

Tri-block copolymer styrene–butadiene (SBS) is extensively applied in bituminous highway construction due to its high elasticity and excellent weather resistance. With the extension of time, tri-block structural SBS automatically degrades into bi-block structural SB- with some terminal oxygen-containing groups under the comprehensive effects of light, heat, oxygen, etc. In this paper, the effects of aging temperature, aging time and oxygen concentration on the molecular structure of thermo-oxidative aged SBS were mainly investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), and the correlation between oxygen-containing groups and thermal properties (TG–DTG) was further discussed. The FTIR and XPS results show that rapid decomposition of SBS will occur with increments of aging temperature, aging time and oxygen concentration, and a large number of oxygen-containing groups such as –OH, C=O, –COOH, etc. will be formed during thermo-oxidative aging. In short-term aging, changes in aging temperature and oxygen concentration have a significant impact on the structural damage of SBS. However, in long-term aging, it has no further effect on the molecular structure of SBS or on increasing oxygen concentration. The TG and DTG results indicate that the concentration of substances with low molecular weight gradually increases with the improvement of the degree of aging of the SBS, while the initial decomposition rate increases at the beginning of thermal weightlessness and the decomposition rate slows down in comparison with neat SBS. From the relation between the XPS and TG results, it can be seen that the initial thermal stability of SBS rapidly reduces as the relative concentration of the oxygen-containing groups accumulates around 3%, while the maximum decomposition temperature slowly decreases when the relative concentration of the oxygen-containing groups is more than 3%, due to the difficult damage to strong bonds on the molecular structure of aged SBS.

Effect of layered double hydroxides on ultraviolet aging resistance of SBS modified bitumen membrane

Layered double hydroxides (LDHs)/styrene-butadiene-styrene (SBS) copolymer modified bitumen was prepared by melt blending. The effect of LDHs on the ultraviolet (UV) aging behavior of SBS modified bitumen was investigated. The changes of chemical structures of modified bitumen before and after UV aging were characterized by Fourier transform infrared spectroscopy (FTIR). The results show that LDHs obviously reduce the variation of softening point and low temperature flexibility of SBS modified bitumen under different UV radiation intensities, which indicates that the UV aging resistance performance of SBS modified bitumen is improved effectively by LDHs. Compared with SBS modified bitumen, the changes of carbonyl, sulfoxide and butadienyl of LDHs/SBS modified bitumen decrease significantly after UV aging according to FTIR analysis, demonstrating that the oxidation and degradation reactions of SBS modified bitumen were restrained effectively by adding LDHs.

Evaluation of aging performance of bitumen containing layered double hydroxides intercalated by UV absorbents

Abstract This paper investigated the ageing behaviour of bitumen modified with organically modified layered double hydroxides (LDH). Two organo-LDHs (OLDHs) intercalated by different UV absorbents, 2-hydroxybenzoic acid (HBA) and 2-hydroxy-4-methoxybenzo- phenone-5-sulfonic acid, were employed to modify one virgin bitumen using a laboratory high-shear mixer, for comparison purposes, a standard LDH was also included as a binder modifier in the experimental investigation. The rolling thin film oven test and UV exposure test were conducted to simulate the short-term and UV ageing of bitumen, respectively, and then the ageing performance of LDH and OLDH modified bitumens was evaluated by analysing the physical and rheological properties and chemical composition. The results showed that OLDH modified bitumens exhibited improved short-term ageing resistance due to the barrier property of layered OLDH to the penetration of oxygen and loss of light components. With respect to the UV ageing, OLDH modified bitumens were found to be less susceptible to UV radiation because of the improved compatibility with bitumen and UV shield effect of OLDH in comparison with LDH. Chemical composition analysis indicated an increase in the concentration of polar fractions resulting from the generation of oxygen-containing functional groups during ageing, leading to an increase of stiffness of bitumen, the increment of polar fraction of OLDH modified bitumens is smaller than that of LDH modified bitumen, exhibiting less ageing degree.