Abstract

The paper presents an analysis of the influence of environmental factors on the cracking susceptibility of asphalt concrete resulting in a change in the durability of asphalt pavement. In order to assess the phenomenon, laboratory tests were carried out taking into account the destructive effects of moisture, freeze-thaw cycle and long-term ageing. The influence of both factors occurring simultaneously was also verified. Due to the different methods of assessing resistance to water and frost, the tests were carried out according to four variants of conditioning the samples: Polish Technical Requirements WT:2-2010 and WT:2-2014, AASTHO (American Association of State Highway and Transportation Officials) T 273, AASHTO TP 140 (MIST). Long-term aging was conducted according to AASHTO R 30 for 120 h and also in extended time to 216 h. Finally, ten variants of conditioning samples were tested. Asphalt concrete for wearing course was investigated. Parameters of mixtures with neat (50/70) and SBS-modified (45/80-55) binders were compared. The evaluation of changes in fracture toughness was carried out based on the results of testing SCB (Semicircular bending) specimens with a 10 mm notch depth at a temperature of +10 °C, at a loading rate of 1 mm/min. Fracture toughness, fracture energy and Flexibility Index were assessed. A group of 40 results for each of the mixtures was obtained, taking into account both the dispersion due to material heterogeneity (four samples for each of the conditioning variants) and variation in material properties caused by environmental factors (10 conditioning variants). The influence of water and frost action causes a decrease in fracture toughness and a reduction in fracture energy. Long-term ageing increases the stiffness of the mixture, thus increasing the fracture toughness. A significant increase in the brittleness of the material is observed, which reduces the deformation at fracture and thus the fracture energy. On the basis of the obtained results, it can be concluded that the destructive effect of environmental factors is clearly more visible in the case of a mixture with a neat binder. The comprehensive laboratory test results allowed for probabilistic analysis and reliability estimation related to the assessment of the durability of asphalt mixtures. It could be concluded that asphalt pavements made with the use of modified bitumen are characterized by significantly higher durability.

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