Study on Cracking Resistance of Basalt Fiber-Reinforced Microbond Asphalt Macadam

The aim of the present study was to explore the effect of basalt fibers on the cracking resistance of microbond asphalt macadam and reduce the occurrence of cracks in asphalt pavements with semirigid base. To this end, compressive resilient modulus tests, rutting tests, and semicircular bending tests were conducted on microbond asphalt macadam with different fiber contents, and the change trends of the compressive resilient modulus, dynamic stability, and flexibility index (FI) with fiber content were revealed. According to the results of this study, the addition of basalt fibers affected the compressive resilient modulus, dynamic stability, and FI of microbond asphalt macadam significantly. With the increase of fiber content, the compressive resilient modulus, dynamic stability, and FI presented a uniform trend of increasing first and decreasing afterwards. When the fiber content was 0.4%, various indices reached their maximum values, suggesting that the cracking resistance of the basalt fiber-reinforced microbond asphalt macadam was optimal under this content. This study is of great significance for the application and promotion of basalt fiber-reinforced microbond asphalt macadam.

Estimating Macrofracture Toughness of Sandstone Based on Nanoindentation

An upscaling method for estimating macrofracture toughness by nanoindentation results was proposed in this study. Grid nanoindentation tests were conducted on sandstone samples to obtain micromechanical properties of indents, including elastic modulus, hardness, and stiffness. Multifactor cluster analysis was then carried out to categorize the sandstone into five mechanical phases. Finally, the macrofracture toughness was predicted by using the macroelastic modulus of the sample and the critical energy release rate of the weakest phase. To verify this method, the upscaling result was compared with the macrofracture toughness measured by the notched semicircular bending (NSCB) test. The discrepancy in the macrofracture toughness from our method and the NSCB test was 8.8%, which was acceptable. Also, it is proved that our method can provide more accurate upscaling results compared to other methods.

Influence of Disc Specimen Configuration on Its Three-Dimensional Dynamic Stress Balance

In order to investigate the dynamic stress balance of different configurations of rock specimens, three-dimensional finite element models of SHPB were established. Five types of configuration disc specimens with a diameter of 75 mm and a thickness of 30 mm were impacted at a speed of 5 m/s using a special-shaped bullet. The propagation laws of stress wave on the contact surface of the specimen-bar and the inside of the specimen were analyzed, and the time history of the stress balance factors at different positions of the specimen was obtained. The results show that the amplitudes of the transmitted waves corresponding to the five types of disc specimens with different configurations have obvious differences, and the stress propagation in the specimen has three-dimensional characteristics. According to the ease of achieving stress balance, the five configuration specimens are ordered by notched semicircular bending disc, flattened Brazilian disc, cracked straight-through flattened Brazilian disc, Brazilian disc, and cracked straight-through Brazilian disc specimen. Among them, only the first three configurations of the specimen reached the stress balance. The dynamic stress balance is affected by the disc loading mode, end contact conditions, the presence of prefabricated cracks, and disc thickness. In addition, as the disc loading end is a processed platform, it is beneficial to achieve stress balance. Prefabricated cracks are not conducive to achieving stress balance. The loading method of the notched semicircular bending disc is more conducive to achieving stress balance. This research has a certain guiding significance for selecting suitable specimen configuration and research methods to carry out rock dynamic fracture experiments.