Although shotcrete reinforced with polypropylene fiber was first used in Europe in 1968, it was not until 1988 that a high volume of polypropylene fiber was successfully used in a shotcrete application. Conditions related to crack resistance and rebounding had resulted in a compromise on steel fiber length, making the mid-range length most commonly specified. Because of the low modulus or flexible nature of the polypropylene fibers, it was hoped that longer fibers and higher volumes could be used without causing problems of manageability in the field.
A research program was undertaken to determine whether or not polypropylene fibers could be readily added, mixed, and pumped in the shotcrete process at high volume levels that would meet established toughness index values. It was found that as fiber length increased for a given volume quantity, the ability of shotcrete to carry load after first crack increased dramatically. The longer fibers were better able to bond or mechanically anchor in the concrete matrix, whereas the shorter fibers tended to pull out. The first actual project to take advantage of these test results was at Oldman River Dam in southern Alberta. They tried the polypropylene fibers at 10.1 pounds per cubic yard. Strength and toughness requirements were met, with the contractor reporting a 19 percent reduction in the fiber reinforcement cost as well as reduced rebound, resulting in further economy.