Following a 3-year development period, a new test for post-crack performance assessment of fiber-reinforced shotcrete (FRS) and fiber-reinforced concrete (FRC) based on round panels was passed by ASTM Committee C 09 in June 2002. The standard test method, known as C 1550-02, œStandard Test Method for Flexural Toughness of Fiber-Reinforced Concrete (Using Centrally-Loaded Round Panel), was published in the 2002 edition of the Annual Book of ASTM Standards V. 4.02.1 Publication of this standard test method is a major development in the fiber-reinforced shotcrete industry. It will, for the first time, permit a both reliable and economical estimation of post-cracking performance for this material.
The use of fibers in shotcrete has become an established form of reinforcement in many sectors of the underground construction industry over the last 20 years. The effective measurement of post-crack performance (toughness) in this material, however, is a problem that has plagued the industry and made the influence of parameters such as fiber type, mixture design, and spraying technique difficult to determine. Much of the difficulty is attributable to the high levels of within-batch variability obtained for even well-prepared sets of FRS samples when beams are used as the basis of toughness assessment. Typical levels of within-batch variability for toughness indices obtained using ASTM C 1018 beams range from 13 to 18%.2,3 More than18% is common for residual strength obtained using EFNARC beams.4 The imprecision associated with such high levels of variability has obscured trends in performance development and eroded confidence in the material. Some improvement occurred with the introduction of EFNARC panels in the 1990s,5,6 but this test suffered its own difficulties associated with seating problems and high costs. Other types of specimens have seen occasional use,7-10 but the size and expense of these tests have limited their use to special applications.
The first round panel test similar to the C 1550 configuration was undertaken in 1997 as part of an investigation of the influence of support conditions on structural behavior in FRC panels.11 The potential of this test was recognized by the Roads and Traffic Authority of New South Wales in Australia, which immediately sponsored a comparative study of FRS performance for several commonly available fibers.12 A specifi-cation based on this test13 was also introduced