Abstract
To reduce the thermal-oxidative aging of asphalt and the release amount of harmful volatiles during the construction of asphalt pavement, a new composite anti-aging agent was developed. Since the volatiles were mainly released from saturates and aromatics during the thermal-oxidative aging of asphalt, expanded graphite (EG) was selected as a stabilizing agent to load magnesium hydroxide (MH) and calcium carbonate (CaCO3) nanoparticles for preparing the anti-aging agents of saturates and aromatics, respectively. Thermal stability and volatile constituents released from saturates and aromatics before and after the thermal-oxidative aging were characterized using the isothermal Thermogravimetry/Differential Scanning Calorimetry-Fourier Transform Infrared Spectrometer test (TG/DSC-FTIR test). Test results indicate that anti-aging agents of EG/MH and EG/CaCO3 effectively inhibit the volatilization of light components in asphalt and improve the thermal stability of saturates and aromatics. Then, the proportions of EG, MH, and CaCO3 added in the developed composite anti-aging agent of EG/MH/CaCO3 are 2:1:3 by weight. EG/MH/CaCO3 plays a synergetic effect on inhibiting the thermal-oxidative aging of asphalt, and reduces the release amount of harmful volatiles during the thermal-oxidative aging after EG/MH/CaCO3 is added into asphalt at the proposed content of 10 wt.%. EG plays a synergistic role with MH and CaCO3 nanoparticles to prevent the chain reactions, inhibiting the thermal-oxidative aging of asphalt.
Highlights
Asphalt is a mixture of hydrocarbon and non-hydrocarbon compounds with very complex components
The decreasing rate of saturates/expanded graphite (EG)/magnesium hydroxide (MH) is much smaller than that of saturates. This indicates that the decomposition reaction and the volatilization of light components in saturates are decreased after adding EG/MH
During the thermal-oxidative aging of saturates. This is because EG/MH plays the filling and stabilizing roles in saturates, and the porous EG has a strong adsorption performance so that some short-chain hydrocarbon molecules are adsorbed by EG [12]
Summary
Asphalt is a mixture of hydrocarbon and non-hydrocarbon compounds with very complex components. Asphalt is one of the most widely used binder materials of pavement engineering in. It is vulnerable to aging during the construction and service life of asphalt pavement. Sunlight, oxygen, and moisture, asphalt becomes harder, leading to a series of pavement distresses such as crack, raveling, pot holes, etc. The released volatile organic compounds are harmful to the natural environment and construction workers’ health when the thermal-oxidative reaction of asphalt occurs at high temperature [2]. Thermal-oxidative aging exists in the construction and service processes of asphalt pavement, including mixing, paving, rolling, Materials 2020, 13, 4005; doi:10.3390/ma13184005 www.mdpi.com/journal/materials
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