Deflection Measurement Considerations in Evaluating FRC Performance Using ASTM C 1018

Abstract

The issue of how the method of determining midspan deflection in American Society for Testing and Materials (ASTM) C1018 toughness tests influences first-crack strength, first-crack deflection, toughness indices, and residual strength factors is addressed by comparing results obtained using the method now required in the current standard. The standard is based on net midspan deflection determined as the nominal midspan deflection minus the average of the deflections measured at the beam supports, with corresponding same-specimen results based on nominal midspan deflection only which was not explicitly excluded in earlier versions of the standard. The problem of dealing with the portion of load-deflection relationship immediately after first crack when it is unstable is also discussed. The range of test specimens for which comparative data are reported includes a series of third-point-loaded beams with three different steel fibers of varying lengths, a second smaller series of beams that allows for assessment of the effects of beam size and fiber alignment, and a series of beams with a single type of fibrillated polypropylene fiber. Fiber contents are varied as well. The results demonstrate the extent to which the C1018 parameters are effective in distinguishing the performance of the various fiber reinforced concrete mixtures in terms of fiber type, geometry, and amount.