Creep of Cracked Polymer Fiber Reinforced Concrete

Creep of cracked polymer fiber reinforced concrete is complex and not well understood. Fiber reinforced concrete creep can be attributed to fiber creep as well as interfacial fiber-matrix creep. The present work discusses the long-term behaviour of individual fibers and short-term bond strength between fiber and matrix. Polypropylene fibers, used as structural reinforcement, are being tested. A novel measuring method was adopted to measure the creep elongation of the fibers. Laser displacement sensors continuously measure the elongation of the fiber at a rate of 1 Hz. Different initial fiber lengths and sustained load levels are considered. The results show that at moderate load levels, the creep strain at failure can be an order of magnitude greater than the instantaneous strain. Additionally, experimental results of pull-out tests of the same fiber are reported. The results suggest that the age of the matrix is not influential in the pull-out behaviour. On the other hand, the matrix composition and imbedded length of the fiber have an important influence on the maximum pull-out force. The fiber embossment can increase post-peak performance. For the reported fiber, a continuous stress buildup and debonding mechanism is proposed to describe post-peak behaviour.