Study on the Fiber-Matrix Bonding Properties of Ultrahigh-Performance Concrete at Multiple Scales

Abstract

This study provides a systematic evaluation of the pullout behavior of steel fibers embedded in ultrahigh-performance concrete (UHPC) with calcium carbonate whiskers and carbon nanotubes at the micrometer and nanoscale levels. This study investigated mechanical and the bonding properties of the matrix at two different scales using the compressive test, flexural test, and single-fiber pullout test, which are important for the further improvement of concrete. The results show that at a specific dosage, both calcium carbonate whiskers and carbon nanotubes effectively improve the compressive and flexural properties of concrete. The pullout behavior at both scales is significantly optimized compared with the reference system. Comparing the bonding strength and pullout energy at the two scales, the calcium carbonate whiskers are better at improving the fiber-matrix bonding properties. Scanning electron microscopy (SEM) was used to observe the pulled-out fibers. The fracture mechanism of the matrix and the influence of the added material on the bonding properties of the matrix were validated microscopically.