Making construction waste into raw materials for recycled concrete is beneficial for resource conservation and environmental protection. This paper investigated the effects of different recycled brick aggregate (RBA) replacement rates (30%, 50%, 70%, and 100%) and different contents of polypropylene fibers (PPFs) (0.08%, 0.10%, 0.12%, 0.16%, and 0.2%) on the mechanical properties of recycled brick concrete. Gray correlation was also used to analyze the degree of effect factors on the mechanical properties of concrete. The results showed that the mechanical properties decreased when the natural coarse aggregate (NCA) was replaced with RBA, while PPFs could better improve the mechanical properties of RBA concrete. The improvement of compressive and flexural properties was optimal when the PPF content was 0.12%; the improvement of tensile properties was optimal when the PPF content was 0.2%. In addition, PPFs significantly improved the toughness of RBA concrete. The gray correlation degrees between compressive strength (tensile strength, flexural strength) and NCA, RBA, and PPFs were 0.8964 (0.8691, 0.8935), 0.7301 (0.6530, 0.7074), and 0.5873 (0.5870, 0.5840), respectively.

Biaxial geogrids are manufactured with ribs oriented in two perpendicular directions to carry loads in these two directions. In real applications, applied loads may not necessarily follow the orientations of these ribs. How the geogrid responds if subjected to a tensile load at different directions is not well understood. In this study, the numerical software — FLAC was adopted to investigate the effect of the loading direction on the stress-strain response of a biaxial geogrid. The geogrid ribs were modeled using beam elements jointed at nodes and subjected to tension in one direction. The numerical results show that the stress-strain responses of the geogrids are different at different loading directions. The tensile strength of the geogrid, when subjected to a load in the direction different from the machine or cross-machine direction, is much lower than that loaded in the machine or cross-machine direction.