The Mechanical Properties and Failure Mechanisms of Steel-Fiber- and Nano-Silica-Modified Crumb Rubber Concrete Subjected to Elevated Temperatures

Steel-fiber- and nano-silica-modified crumb rubber concrete (SFNS-CRC), a new kind of environmentally friendly concrete, is characterized by its high performance. It achieves the recycling and reuse of waste rubber and promotes sustainable development in the rubber industry. This study used 12 groups of 288 specimens to study its mechanical properties and failure mechanisms when subjected to elevated temperatures. In the experiments, a heating and loading apparatus invented in our laboratory was used. The chosen crumb rubber concrete contained 5% rubber by volume. Through specimen analysis, the failure modes, mass loss, and compressive and splitting strengths of the specimens, as well as their failure mechanisms, were tested and are discussed while taking into account three variables, namely steel fiber volume ratio (0%, 0.5%, 1.0%, and 1.5%), nano-silica content (0%, 1%, and 2%), and temperature (20 °C, 200 °C, 400 °C, and 600 °C). The test results indicate that the typical damage shapes of CRC subjected to elevated temperatures can be significantly ameliorated through the addition of steel fibers and nano-silica. This can lead to evident improvements in brittle failure and render CRC ductile. Essentially, it improves the integrity of SFNS-CRC specimens. The compressive and splitting tensile strengths of concrete mixtures subjected to elevated temperatures increase with an increase in the steel fiber content. There is an obvious improvement in the compressive strength when subjected to elevated temperatures and after adding nano-silica. The CRC with a content of 1.0% steel fiber is optimal, and the optimal content of nano-silica is 1.0%. In addition, SFNS-CRC performs better in terms of mechanical properties when subjected to elevated temperatures. The splitting tensile strength of SFNS-CRC is improved using steel fibers, and nano-silica plays a crucial role in improving compressive performance. SEM and XRD analyses helped verify the test results.