Assessment of Variation in Strength from Surface of Concrete Using Modified Pull-Off Method

Abstract

A modified pull-off method, which was developed to assess the tensile strength of surface layers of concrete, is described. The modified pull-off method enabled the measurement of tensile strength at an arbitrary depth from concrete surface using a circular steel probe with a hollow cylinder. In this paper, the basic characteristics of the modified pull-off method were investigated. As for the influencing factors to exert on the test values, the effects of depth of core slit, core diameter, maximum size of coarse aggregate, and the moisture content were examined. In addition, the relationships of the pull-off tensile strength with the splitting-tensile strength and the compressive strength which was also estimated from the rebound number, the pulse velocity and the pin-penetration depth, were also examined. The applicability of the test was also examined by applying it to the surface layer of concrete cast using mold lines with permeable sheets. When applied to the damaged concrete due to freezing-thawing cycling in the laboratory, it was observed that the relationship between the depth of damaged concrete estimated from the pull-off tensile strength and freezing-thawing cycles could be expressed by a power expression. This suggests the possibility that the thickness of the damaged section can be predicted at the required freezing-thawing cycles.