Structure and mechanical properties of steel fiber, basalt fiber, and carbon fiber modified concrete

In this study, the workability, mechanical properties, failure mode, and microstructure of three types of fiber (steel fiber, basalt fiber, carbon fiber) modified concrete are characterized. The addition of steel fiber ≤ 40 kg/m³ or basalt fiber ≤ 6 kg/m³ shows little effect on the slump of concrete, there is an obvious decrease in slump as the carbon fiber addition exceeds 3 kg/m³. For steel fiber concrete, the relatively high 14-day mechanical properties belong to the 40 kg/m³ addition, with a compressive strength of 99.1 MPa and a bending strength of 18.5 MPa. The optimal addition of both basalt and carbon fibers is 3 kg/m³. For basalt fiber modified concrete, its 14-day compressive strength and bending strength are 111.1 MPa and 18.6 MPa respectively, and that for carbon fiber are 110.6 MPa and 18.2 MPa. Basalt fiber mainly reinforces concrete by its fracture energy, leading to brittle failure of specimens; whereas carbon fiber mainly relies on fiber pull-out to restrain the transverse expansion deformation of concrete, resulting in ductile failure of specimens. Consequently, the 3 kg/m³ carbon fiber-modified concrete with excellent mechanical strength and toughness is more suitable for building structures.