Flexure testing made easy using the UNB "superflexomatic"

Abstract

Concrete is a very brittle material which has very little strength after the concrete matrix has cracked. To improve the ductility of concrete, reinforcing is added. One type of such reinforcing is in the form of discontinuous fibres. This is used as secondary reinforcing to control cracking of the member. In order to measure the amount of residual strength, after cracking, in a fibre reinforced member, the ASTM C 1018 standard for measuring flexural toughness is used. There have been concerns over the accuracy of such tests, due to error introduced by settlement of beam supports. The goal of this report is to design and test a yoke which is to be used to measure beam deflection. The purpose of the yoke is to eliminate errors caused by support settlement. Several fibre reinforced flexure specimens were tested using the yoke, as well as other methods to measure mid-span deflection. The results show that other methods used to measure mid-span deflection can be as much as 40 times greater than theoretical values, while measurements using the yoke are almost exactly the same as theoretical values. Overall, this report will show that using the yoke is far more accurate for measuring mid-span deflections than previous methods.