A Method of Measuring the Displacement of an Ultra-High-Performance Fiber-Reinforced Concrete by Means of Unbound Gages

A study on Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) required accurate continuous displacement measurements to fully understand specimen compressive and split tensile behavior. From uniaxial compressive testing, load, and displacement data was acquired to develop specimen specific stress–strain diagrams from which the modulus of elasticity and strain at ultimate capacity of the material were found. Thus, a device suitable to measure the displacement and crack width opening was required during testing to gain knowledge of the behavior of UHPFRC subjected to compressive and tensile loads. The device normally used to measure average displacement is typically not used for ultimate strain conditions because of the potential LVDT damage from the often explosive compression failure of concrete specimens. Hence, this study investigated the use of Local Deformation Transducers (LDTs), which consists of strain gages attached at mid-length on a narrow strip of highly flexible and resilient material. Data collected from these gages corresponded well with UHPFRC test data collected from other institutions using more complex methods and proved to be a reliable source of measuring displacements with the intent of identifying modulus of elasticity, and concrete strains at first crack, and ultimate capacity for an UHPFRC.