Influence of Test Machine Control Method on Flexural Performance of Fiber Reinforced Concrete Beams

Abstract

Abstract Flexural testing of fiber reinforced concrete (FRC) and shotcrete using beams has undergone a steady evolution over the past 30 years to the point where complex servo-controlled test machines are now required to undertake these tests. These machines have been found necessary in order to impose stable and reproducible test conditions on beams. Servo-controlled machines utilize closed-loop strain feedback mechanisms in an attempt to maintain stability throughout the post-crack deformation history of a brittle FRC specimen. However, some standard test methods for flexural performance assessment of FRC require displacement-control of the loading piston rather than strain-control based on the measured deformation of the beam. Displacement-control has frequently been found to result in unstable unloading of brittle FRC. Anecdotal evidence suggests that differences in the method of machine control may lead to changes in the apparent performance of specimens. An investigation was therefore instigated to examine the apparent performance of FRC beams tested using strain-controlled loading compared to displacement-control.