Around 1960, the industry began investigating the use of synthetic fibers to improve the performance of concrete. A January 1976 article reported that of several synthetic materials all but polypropylene had been ruled out, and the applications for polypropylene were still “somewhat limited.” By 1983, these fibers were in general use, but ASTM and ACI were still working on standard tests for measuring the properties of fiber-reinforced concrete. A photo from June 1983 shows polypropylene fibers as manufactured (left) and as they appear when mixed in concrete.