Strain measurements on saturated concrete specimens

Summary A programme of work on the mode of deformation and failure of plain concrete has called for the measurement of local tensile strains on the surface and the over-all deformation of saturated, as well as dry, concrete test specimens. Two different strain-measuring techniques have been developed to give this information. In the first, electrical resistance strain gauges, suitably protected, are attached to the mould and cast in situ. These local in-surface gauges are located just beneath the plane of the surface of the specimen. In the second technique, detachable gauges of any length and suitable for measuring over-all strains are manufactured by attaching electrical resistance strain gauges to Perspex strips or rings. Details are given of the methods of manufacture and use of the gauges and comparisons are made between the strains measured with the in-surface and on-surface foil gauges and roller extensometers. The different values obtained imply that the gauges and extensometers are measuring basically different properties of a deformed concrete specimen, and when absolute strain measurements are required this should be recognized.