Abstract
Moisture susceptibility and cracking are considered as two major causes of distress in asphalt pavement, which are developed and expanded under environmental factors such as Freeze-Thaw Cycles (FTC) and traffic loading. These causes of distress may be controlled by improving two factors of bituminous phase cohesion and adhesion between aggregates and bitumen. This article was aimed to study the rheological properties of bitumen, such as rotational viscosity, as well as the mechanical properties of asphalt mixture, such as moisture susceptibility, fracture resistance, and fracture brittleness, by using two additives, carbon black and hydrocarbon, which were obtained from the pyrolysis recycling of hospital waste caused by Covid-19. In this regard, a total of 8 mixtures were made, including a mix without any additive, three mixes of 1.25, 2, and 2.75 % hydrocarbon, three mixes of 6, 12, and 18 % carbon black, and a mix of 2.75 % hydrocarbon + 18 % carbon black. In order to determine the effect of FTC on the asphalt samples and to adapt the laboratory conditions to the road conditions, 1 and 3 cycles of Freeze-Thaw Damage (FTD) were applied, respectively, indicating 4 and 12 years of pavement distress. The results showed that the addition of different percentages of carbon black and hydrocarbons (separately and together) through improving bituminous phase cohesion and adhesion between aggregates and bitumen increased the samples resistance to the moisture susceptibility. It was also found that fracture energy (GF) and fracture toughness (KIC) of all mixes improved compared to the base sample. At last, the results of brittleness indicators revealed that all mixes containing 6, 12, and 18 % carbon black and 1.25, 2, and 2.75 % hydrocarbon had a more flexible behavior than the base mix under 1 cycle of FTD; while the mixes containing 18 % carbon black and 2.75 % hydrocarbon were just flexible under 3 cycles of FTD. Accordingly, it can be concluded that a mix containing 2.75 % hydrocarbon + 18 % carbon black had the best results in terms of viscosity, moisture susceptibility, and fracture resistance (under 1 and 3 FTD cycles).
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