| Summary: | The UV aging of bitumen has a significant influence on the pavement service life, therefore, the research on UV aging has attracted increasing attention recently. It is known that the aging of bituminous pavements does not occur instantly through the full depth, instead, the aging depth of the bitumen increases gradually with the increasing aging time. The limitation of the research is that the development mechanism of the aging depth of bitumen is not clearly known. Various thicknesses of bituminous membranes were prepared and the UV light transmission and absorption properties of bituminous membranes were investigated by UV–visible spectrophotometric, aiming to determine the penetration depth of UV light in bitumen after UV aging. It is concluded that, for the same bituminous membrane, the transmittance of UV light increases with the increase of the light wavelength; while the transmittance of UV light decreases significantly with the increase of bituminous membrane thickness. The penetration depth of UV light in bitumen increases gradually with increasing UV aging time. The relationship between UV light penetration depth in bitumen and aging depth of bitumen was analyzed, and UV aging models of three parts of bitumen were established to reveal the development mechanism of the UV aging depth of bitumen during UV aging. The increasing aging depth of bitumen is due to the increase of UV light penetration depth in bitumen, and the diffusion action of aging products from surface bitumen to deeper bitumen. During the UV aging, the bitumen actually comprises three parts, namely, the surface direct aging part (UV light can reach), the deeper diffusion aging part (aged by the diffusion action) and the internal unaged part (UV light and diffusion action can not affect).
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