For performance-based specifications and design processes, a number of cracking-related index parameters have been proposed for asphalt mixtures in recent years. A number of these parameters have been developed to utilise results from fracture tests. This study conducted a comprehensive evaluation of various fracture index parameters including fracture energy, Illinois flexibility index, stress intensity factor and toughness index. Over 200 tests from 61 distinct test data sets representing 21 asphalt mixtures are included. The focus of this study is on low-temperature cracking and all indices were evaluated using test results from the disk-shaped compact tension fracture tests conducted at low temperatures. The objective of this study was to determine if there is a relationship between various fracture index parameters as well as to determine typical measurement variability associated with each parameter. Comparisons were made between different indices and correlations were determined for the mix rankings provided by individual indices. The results indicate that fracture energy successfully captured the mix rankings and showed a strong correlation with other indices. In order to better capture post-peak softening behaviour of asphalt mixtures, the flexibility and toughness indices have been utilised; however, these parameters were found to have high variability. A new index called fracture strain tolerance has been proposed that was shown to provide the same level of distinction between mixtures as the flexibility and toughness indices while having considerably lower variability. Finally, several areas were identified for future extension of this research.

Oxidative age hardening of bitumen results in increasing fatigue susceptibility of bituminous mixtures, thus reducing the service life of asphalt pavements. Polymer additives to bitumen have been shown to improve its viscoelastic properties and, in some cases, reduce the level of bitumen hardening. Fourier transform infrared (FT-IR) spectroscopy enables evaluation of oxidation levels in bitumen by measuring the concentration of oxygen-containing chemical functionalities. This paper summarizes the results of the investigation of oxidative age hardening of polymer-modified bitumens (PMB) caused by accelerated aging in laboratory conditions. The PMB samples are prepared with different concentrations of styrene–butadiene-based co-polymers. Next, the PMB samples are aged using standard procedures that employ air blowing at 163 °C for 85 min followed by conditioning the samples at 100 °C and 2.1 MPa pressure for 20 to 48 hours. The resultant changes in their chemical composition are evaluated by portable attenuated total reflection (ATR) spectrometer. Measurements of ketone, sulfoxide, and hydroxyl content in PMB samples indicated similar oxidation pathways to those of non-modified bitumens. In addition, no evidence of polymer degradation due to accelerated aging of PMB was found in this study.

Application of geogrids for asphalt layers in road and airport pavements has been studied since early 1980s. This type of geosynthetics is feasible to mitigate reflective cracking and to prolong fatigue life, that is, to reinforce asphalt layers within pavement structure. Up to now, many laboratory and field studies demonstrated significant benefits of using geogrids but still several aspects of their working mechanism within adjacent asphalt layers remain not fully understood and need to be further explored. This paper presents an initial part of the long-term study initiated in Poland in order to fully assess the benefits of using geogrids within asphalt layers. The first part of this paper presents the state-of-the-art review on geogrid applications in asphalt layers. The next part demonstrates and discusses the results obtained on the geogrid-reinforced beams under monotonic and cyclic loading conditions. Three types of large beams were prepared in the laboratory conditions. One group comprises reference beams without any reinforcement and the other two were reinforced, respectively, with glass and carbon geogrids. Specimens were evaluated in a custom-made 3PB/4PB fixture at 13°C in order to observe their behaviour under force-controlled fatigue test and displacement-controlled fracture test. Results demonstrated a beneficial impact of fibre reinforcement on the development of beam deflections in the fatigue tests and significantly higher fracture energy in the post-peak softening region. These results will be used to prepare a new experimental campaign to closely investigate the reinforcement mechanism of geogrids within asphalt layers. The paper concludes with short- and long-term plans necessary to develop an official design procedure for the pavements with geogrid-reinforced asphalt layers in Poland.