Aging mechanism of foamed asphalt under the coupling effect of salt-water-temperature

Compared to the hot-mixed asphalt, foamed asphalt significantly reduces harmful gas emissions and energy consumption. However, the effect of water usage on the performance and aging characteristics of foamed asphalt remains inconclusive. This study investigates the aging characteristics of foamed asphalt under the coupling effect of salt-water-temperature using atomic force microscopy (AFM) and Fourier-transform infrared spectroscopy (FTIR). Liaohe 90# asphalt and foamed asphalt with two foaming water contents (1.8 % and 5 %) were subjected to salt-freeze-thaw-dry-wet cycles for several times, respectively. The micro-morphology, modulus, adhesion and chemical functional groups of the specimens were obtained from the tests, and the correlation between the micro-property indexes and the macro-property indexes was analyzed. The results show that the microstructure of foamed asphalt tends to ‘homogenise’ as the number of freeze-thaw and wet-dry cycles increases; the roughness index decreases; the modulus and adhesion increase; the aromatic and sulphoxide indexes become greater. Taking the foamed asphalt FWMA-1.8 as an example, the modulus increased from 85.6 MPa to 119.6 MPa, with an increase of 39.72 %; the adhesion increased from 14.5nN to 16.3nN, with an increase of 14.5 %. The aromatic indices increased by 33.35 %, the sulphoxide indices increased by 155.55 %.There is a good correlation among sulphoxide indexes with the needle penetration(R 2 =0.74) and softening point(R 2 =0.73). Under the coupling effect of salt-water-temperature, the foamed asphalt experienced aging, the asphalt became hardened, and the asphaltene content increased. It was also revealed that the foaming water and foaming process affected the microstructure and chemical components of foamed asphalt. Excessive water consumption for foaming accelerates the deterioration of foamed asphalt. The results of the study provide some guidance for the popularization and application of foamed asphalt mixtures in the freezing zone. It is also important to further understand the aging process of foamed asphalt under salt-water-temperature coupling. • The effect of salt-water-temperature coupling on the ageing of foamed asphalt was investigated. • The aging process of foamed asphalt under salt-freeze-thaw-dry-wet cycling conditions remains in its initial stages. • The foamed asphalt aging under salt-water-temperature multifactorial coupling is primarily characterized by macromolecular formation. • Excessive water consumption for foaming accelerates the deterioration of foamed asphalt.