ELECTRONIC-METHODS FOR DETERMINING YOUNG'S MODULUS AND POISSON'S RATIO OF PORTLAND CEMENT CONCRETE

摘要

The purpose of this task was to develop improved methods for determining Young's modulus and Poisson's ratio of portland cement concrete. This report describes the development effort and presents the results of comparitive tests of various electronic and mechanical strain-measuring devices used on cylindrical concrete specimens.nExperiments were made with three separate methods of measuring longitudinal strain. Electrical resistance strain gages were mounted directly on the surface of the concrete, and a technique was developed for their attachment to damp concrete;a hoop transducer device utilizing electrical resistance strain gages was designed;and compressometers were used for mechanical measurements. Lateral strain meas¬urements were made with surface-mounted electrical resistance strain gages and with mechanical compressometers, and an experimental cantilever transducer device was designed and tested.nThe surface-mounted strain gages were demonstrated to provide a highly accurate method for determining Young's modulus and Poisson's ratio. The hoop device provides a highly reliable method for determining Young's modulus. The experimental cantilever transducer proved unsatisfactory.nThe Young's modulus test results with the surface-mounted strain gage method and the hoop transducer method were in close agreement;agreement between these two methods and the compressometer method were only fair. Variations either in gage lengths or in the circumferential position of the measuring device on the con¬crete cylinder caused wide variations in values of Young's modulus.nFor one-time determinations of concrete properties, use of the mechanical compressometer is deemed sufficiently accurate in view of the many variables involved. For time-dependent determinations of longitudinal strains, either the surface-mounted electrical resistance strain gages or the hoop transducer devices are preferred because the gage position can be held constant, whereas the mechanical compressometer is usually reapplied for each successive strain measurement.