Low-temperature cracks (LTC) and intermediate-temperature cracks (ITC) are two important types of cracks in asphalt mixtures that cause damage to pavements and incur high maintenance costs on roads. On the other hand, temperature cycles, in addition to the traffic load on the asphalt mixtures, increase the possibility of structural failures. Therefore, it is necessary to study the solutions to deal with and control this type of cracking using appropriate methods. In this study, an attempt was made to evaluate the effect of amorphous poly alpha olef in (APAO) additive on the LTC and ITC behavior of Hot Mix Aspahlt (HMA) under loading conditions of modes I and II under constant temperature (CT) and variable temperature (VT) cycles. For this purpose, two geometries called symmetric specimen SCB (contains a vertical crack with an angle of 90◦) and classical-modified specimen SCB-2 (contains an angled crack with an angle of 35◦) were selected to simulate the loading conditions of mode I, as well as two geometries called modified specimen SCB-1 (contains a vertical crack with a 90-degree angle) and modified specimen SCB-2 (contains a vertical crack with a 90-degree angle) were selected to simulate mode II loading conditions. A total of four HMA mixtures were made, including one mixture without additives and three mixtures containing 3, 6, and 9 % APAO additives. Next, in order to simulate and match the road conditions with the laboratory samples, CT and VT conditions were applied to all samples. At temperatures of ± 15 ◦C, two fracture resistance indices called fracture toughness (KIC and KIIC) and fracture energy (GF) were studied to investigate the fracture behavior of HMA mixtures. Also, two other fracture indices, namely the Tensile Stiffness Index (TSI) and the Tensile Strength (TS), which represent the fracture behavior of the HMA mixture before the peak load, were evaluated. Finally, the flexibility of the mixtures was evaluated using brittleness indices such as the Flexibility Index (FI), Cracking Resistance Index (CRI), and Toughness Index (TI). The results showed that the fracture toughness and fracture energy of the HMA mixture containing 9 and 6 % APAO increased in mode I and II loading conditions under both CT and VT cycles compared to the base mixture. At temperatures of ± 15 ◦C, from the point of view of the fracture toughness index, the potential for creating angular cracks, and from the point of view of the fracture energy index, the full fracture potential of the mixture containing vertical cracks was higher (under CT and VT cycles). On the other hand, the reduction of the flexibility of the mixtures containing APAO percentages was concluded using FI, CRI, and TI indices. Also, the results showed that the addition of 3, 6, and 9 % of APAO additive to the HMA mixture increased the maximum preload indices, namely TSI and TS, and as a result, increased resistance to elastic deformation.

Keywords