Fiber reinforced concrete (FRC) is finding increased use in construction. FRC offers several advantages over rebar or wire mesh reinforced concrete including increased crack resistance, ductility, energy absorption, impact resistance and residual strength. FRC can also significantly lower materials and labor costs compared to rebar or wire mesh reinforced concrete. The strength of FRC is strongly dependent on the type, size, shape, and amount of fiber used, and testing is required to determine the correct proportions for each application. ASTM C1609 describes the methodology for testing the flexural strength of rectangular FRC beams with dimensions of either 4 x 4 x 14 inches or 6 x 6 x 20 inches.
A mechanical testing machine equipped with the appropriate bend fixture, two displacement transducers, and software capable of controlling the test and recording/analyzing the data is required. The test machine operates in compression at very slow test speeds under closed loop deflection rate control. Electro-Mechanical testers are preferred for control at these test speeds.
A “third-point loading” fixture is used with two support points below the beam and two loading noses on the top of the beam. A fixture is mounted on the beam’s neutral axis directly over the supports.
Two displacement transducers, one on each side of the beam, are mounted to the jig mid-span to measure beam deflection. The outputs of the transducers are averaged together to provide the net deflection measurement. This configuration ensures accurate measurement of mid-span deflection and minimizes errors due to concrete specimen twisting or seating in the supports.
Changes to the ADMET’s ASTM C1609 three-point bend fixture include:
Loading nose designed per ASTM C78
Bottom brackets designed according to ASTM C1812
For a summary of the test, click the Testing Procedure tab. If you need to perform these tests, please read the entire specification from the relevant ASTM publication.