Load relaxation in steel fibres embedded in cement matrices

Twenty-four hour load relaxation curves were obtained from single fibre pull-out specimens with 60 and 80% of the peak pull-out load applied as the initial load. Two fibre types, hooked and crimped, and two matrices, cement paste and microsilica cement paste, were investigated. Tests were conducted at the ages of 1, 7 and 28 d. Two test temperatures of 22°C and 100°C were chosen

Relaxation, as defined by the percent reduction in the applied initial load, was found to decrease with age and was found to increase with the applied initial load; microsilica addition resulted in a reduced relaxation. Hooked fibres were found to relax more than the crimped fibres. A high temperature of 100°C was found to significantly increase the relaxation. After 24 h of relaxation, the specimens, in general, had a poorer pull-out performance as measured by the peak pull-out load and the pull-out energy, compared to the virgin specimens.