Comparison of different approaches for determining the residual post-cracking strength index of fiber reinforced concrete for bridges

摘要

In Canada, there are different approaches to evaluate the performance of fiber reinforced concrete (FRC) for bridges based on the residual post-cracking strength index (R-i). They involve different combinations of test methods ASTM C78, ASTM C1399, and ASTM C1609. The aims of this study were to assess all possible (existing and new) methods to determine the Ri values, and capture the major differences between the current Canadian Highway Bridge Design Code (CHBDC S6-14) and the City of Winnipeg specification's approaches, as a case study. Flexural tests (ASTM C78, ASTM C1399, and ASTM C1609) were performed on 60 FRC beams (100 mmx 100 mmx 350 mm) prepared from concrete provided by four ready-mix concrete suppliers according to City of Winnipeg's bridge deck specifications for a project built in Winnipeg. The results showed that all the methods implemented herein for calculating the R-i of FRC gave comparable results. However, by using Method V, all required parameters (first peak load and residual loads at specified deflections) could be directly extracted from one load-deflection curve obtained from ASTM C1609. In addition, when using this method, the Ri can be calculated for each specimen, which enables quantifying the magnitude of variation from average values. Since this approach also requires fewer number of specimens, reducing time and cost of testing, it has been adopted by the City of Winnipeg in bridge specifications for FRC.