Principle and Implementation of Incorporating Nanomaterials to Develop Ultrahigh-Performance Concrete with Low Content of Steel Fibers

The effect of nanomaterials on the microstructure of ultrahigh-performance concrete (UHPC) has been intensively studied, but the relationships between the macroscopic flexural failure process and microstructures of nanomaterials modified UHPC and the influence of nanomaterials on flexural-tensile stress transfer mode between the UHPC matrix and steel fibers are still not clear. Understanding the relationships will assist in guidance development considering the use of nanomaterials to control the flexural performance of UHPC with low content of steel fibers. Therefore, this paper investigated the influence of nanomaterials on the flexural failure process of UHPC and unlocked the flexural-tensile stress transfer mode between the nanomodified concrete matrix and steel fibers. Owing to the modification effect of nanomaterials on the UHPC matrix as well as the interface and cobearing capacity between the matrix and steel fibers, the flexural-tensile stress transfer mode in UHPC composites conforms to isostrain parallel model. This significantly prolongs the elastic stage before initial cracking and increases the growth slope of fiber reinforcement stage after initial cracking, thus enhancing the flexural strength, compressive strength, and flexural toughness of UHPC with mono 1.2% by volume steel fibers by 45.8%, 62.2%, and 40.2%, respectively. The synergistic enhancement mechanisms of steel fibers and nanomaterials will enable the development of UHPC with a low content of steel fibers and high ratio of strength-to-density.