Fiber-reinforced concrete containing ultra high-strength micro steel fibers under active confinement

This paper presents an experimental study on the compressive behavior of steel fiber-reinforced concrete (SFRC) under active confining pressure. Four different SFRC mixes containing ultra high-strength micro steel fibers at two volume fractions of 1% and 2% were prepared to produce concretes with two different target compressive strengths of 50 and 100 MPa. The active confining pressure was applied on SFRC using a Hoek cell at different confinement levels of 5, 10, 15, and 25 MPa. The effects of confining pressure and steel fiber volume fraction on the compressive behavior of concrete were examined through the axial compression tests on unconfined and actively confined SFRCs. The results show that the axial strength and peak axial strain of SFRCs increase with an increase in the fiber volume fraction. The fiber volume fraction also affects the post-peak branch trend of the axial stress-strain relationships of SFRCs under a given confinement level. SFRCs with a higher volume fraction exhibit more shallow post-peak branches than those of SFRCs with a lower volume fraction. The results also show that the axial strain of SFRC at a given lateral strain increases with an increase in the volume fraction, indicating a reduced rate of dilation of SFRCs at a higher volume fraction. These promising findings point to the great potential of the use of ultra high-strength micro steel fibers in the development of high performance composite structural members in applications where the concrete will be subjected to lateral confinement.