Microcracking and Engineering Properties of High-Strength Concrete

摘要

An X-ray technique was used to study internal microcracking. Two classification systems were developed to analyze the microcracks: bond-mortar crack analysis and simple-combined crack analysis. Internal microcracks were observed at four strain levels. The observed microcracking mechanism is related to the failure mode in uniaxial compression. The results of the mechanical properties study are presented including data on compressive strength, strength gain with age, specimen size effect, static modulus of elasticity, Poisson's ratio, modulus of rupture, tensile splitting strength, unit weight, and drying effect on compressive and flexural strength of normal- and high-strength concretes. A criterion for definition of failure in uniaxial compression for the concretes tested is presented. Failure is considered to occur at the discontinuity point defined as that point when a self-propagating microcracking mechanism is developed, eventually causing disruptive failure with time. The predicted stress and strain ratios at discontinuity are compared to those at which sudden changes occur in Poisson's ratio and volume change curves.