Abstract
Strong ultraviolet light and low-temperature are the typical environmental characteristics in high-altitude areas. The performance of SBS-modified asphalt in the above environmental characteristics needs further study. To improve the resistance ultraviolet (UV) ageing and low-temperature performance of copolymer- (SBS-) modified asphalt, an SBS-modified asphalt containing nano-ZnO and nano-TiO2 is proposed. In this paper, nano-ZnO, nano-TiO2, and SBS were used as modifiers with the silane coupling agent (KH-560) as the nanomaterial surface modification. The orthogonal test table was used to analyse the effects of the three modifiers on the physical properties of modified asphalt at different dosages. On this basis, the physical properties, low-temperature properties, and ageing indices (carbonyl index and sulfoxide index) were studied for base asphalt, SBS-modified asphalt, nano-ZnO/SBS-modified asphalt, and nano-ZnO/nano-TiO2/SBS composite-modified asphalt before and after photoaging. The content changes of characteristic elements (Zn and Ti) in the nano-ZnO/nano-TiO2/SBS composite-modified asphalt before and after ageing were studied by scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), and the UV ageing mechanism was revealed. The results indicate that two nanoparticles show the best compatibility with asphalt after surface modification and can improve the binding ability between SBS and base asphalt. The orthogonal test analysis shows that nano-ZnO has a highly significant effect on the low- and high-temperature performance of the nano-ZnO/nano-TiO2/SBS composite-modified asphalt, and nano-TiO2 has a significant effect on the high-temperature performance. Three optimal composite-modified systems for base asphalt including 4% nano-ZnO/1.5% nano-TiO2/3.2% SBS were proposed and had the best antiaging ability. Compared with the sulfoxide index, the carbonyl index changed most obviously before and after ageing. Additionally, the results reveal that nano-TiO2 has a good absorption effect at a wavelength of 365 nm (ultraviolet light), while nano-ZnO is liable to photolysis, and its activity decreases at this wavelength.
Highlights
In highway pavement engineering at high altitudes, the styrene-butadiene-styrene (SBS) block copolymer-modified asphalt is mostly used as a binder in the surface layer
Zhu investigated the effect of nano-ZnO on pavement performance of SK-70 base asphalt through differential scanning calorimetry (DSC), dynamic shear rheometer (DSR), and Brinell viscometer, and the results showed that nano-ZnO could improve significantly the low-temperature ductility, high-temperature rutting resistance, and ageing resistance of asphalt [10]
Zhang Hongliang et al indicated that the rutting factor of 3.0% nano-ZnO/0.5% nano-TiO2/3.7% SBS-modified asphalt at 88°C is 2.2 kPa which is above the limit (1.0 kPa) provided by AASHTO [30]. erefore, the suggested asphalt formula meets the requirements of high-temperature stability
Summary
In highway pavement engineering at high altitudes, the styrene-butadiene-styrene (SBS) block copolymer-modified asphalt is mostly used as a binder in the surface layer. Compared with the UV ageing of the base asphalt, the SBS-modified asphalt is affected by the base asphalt and SBS modifier; for example, the content of asphaltene depends on the synergistic effect between them [4,5,6]. Butadiene in SBS copolymers is degraded, the base asphalt is oxidized, and the ageing indices (sulfoxide index and carbonyl index) gradually increase. Eir interaction can effectively delay the ageing rate of SBS-modified asphalt [5, 7]. Due to the considerable difference in physical properties between SBS copolymers and base asphalt [7, 8], the compatibility and dispersion of SBS-modified asphalt are generally poor, which affects the ageing resistance of the modified asphalt
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