Toshiro Kamada

THE EFFECTS OF SURFACE PREPARATION ON THE FRACTURE BEHAVIOR OF ECC/CONCRETE REPAIR SYSTEM

Abstract This paper presents the influence of surface preparation on the kink-crack trapping mechanism of engineered cementitious composite (ECC)/concrete repair system. In general, surface preparation of the substrate concrete is considered essential to achieve a durable repair. In this experiment, the “smooth surface” system showed more desirable behavior in the crack pattern and the crack widths than the “rough surface” system. This demonstrates that the smooth surface system is preferable to the rough surface system, from the view point of obtaining durable repair structure. The special phenomenon of kink-crack trapping which prevents the typical failure modes of delamination or spalling in repaired systems is best revealed when the substrate concrete is prepared to have a smooth surface prior to repair. This is in contrast to the standard approach when the substrate concrete is deliberately roughened to create better bonding to the new concrete.

Tension softening diagrams and evaluation of properties of steel fiber reinforced concrete

Abstract For a better understanding of the fracture behavior of concrete structures, knowledge of the post-cracking behavior of concrete material is essential. The tension softening diagram can describe the post-cracking behavior of concrete in tension. In this paper, the properties of various kinds of steel fiber reinforced concrete (SFRC) were evaluated by means of the tension softening diagrams, after discussion of the applicability of the fictitious crack model to SFRC. The fracture energy of conventional SFRC was independent of the specimen size. For the evaluation of the properties of SFRC with different matrix strength, the shape of the tension softening diagram and the fracture energy were superior to the flexural strength. The fracture energy of SFRC with high strength matrix was dependent on the tensile strength of the steel fiber.

NON-DESTRUCTIVE EVALUATION FOR HORIZONTAL CRACKS IN EXISTING RC SLABS BY ANALYSIS-AIDED IMPACT ELASTIC-WAVE METHODS

In this study, impact elastic-wave method was performed at the bottom surface of RC slab cut from an existing highway bridges to survey the horizontal cracks. Before measurements by impact elastic-wave method, impact response analysis was applied to determine optimal steel ball diameter, distance between impact point and receiving point of elastic-wave. Efficiency of analysis-aided impact elastic-wave method was confirmed by drilling and observing the interior of the RC slab by stick scanner. Evaluation results by this method agreed well with results of visual inspection. Thus, validity of the analysis-aided impact elastic-wave method on detection of horizontal cracks in RC slabs of highway bridges was demonstrated.