Direct tension tests for determining the relationship between tensile stress and crack opening of ultra-high performance concrete

Abstract

This study reports the test results of direct tension tests of ultra-high performance concrete (UHPC) and ultra-high performance fiber reinforced concrete (UHPFRC). The idealized model of tensile stress versus crack opening was described for the prediction of tensile behavior. The mixtures of UHPC and UHPFRC were designed to achieve a compressive strength of 200 MPa. The direct tension tests were conducted on the prisms of 40x40x80 mm with notches of 5x5 mm in the middle of the prisms. The test results indicated that UHPC prisms failed in a brittle manner with a sudden drop of load in the descending branch, while UHPFRC prisms failed in a ductile manner with a strain hardening stage after the cracking stress and with a softening stage after the ultimate stress. The crack opening of UHPFRC prisms was much higher than that of UHPC prisms. The values of cracking stress, ultimate stress, and crack opening were significantly improved by increasing the volume of steel fibers from 1% to 2%. The prisms with small dimensions were adopted for the direct tension tests in this study, thus leading to the feasibility of testing and reducing the cost.