Concrete Research and Technology

Granulated concrete samples obtained from the upper surface of deteriorated RC slabs under the surface asphalt layer of a road were examined by microscopic technique and chemical analyses. The muddy components in the granulated concrete were composed of fine-granulated cement pastes and externally invasive clays and asphalt. Deicing salts were thought to be involved in the granulation of concrete, because calcium hydroxide had completely disappeared from the cement pastes although carbonation was not observed. The granulation was considered to be triggered by cracks caused by re-bar corrosion or an alkali-silica reaction. It was estimated that the progress of granulation was due to a complex mechanism of physical action by repetition loads and chemical action by deicing salts.

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In this research, an improved analytical model of indirect joints in seismic retrofit method using steel braces was developed, and three-dimensional FEM analyses of direct shear test specimens of the indirect joints were carried out by using this model. The analytical results corresponded well to the test results. The authors conducted an analytical evaluation to clarify the shear transfer mechanism of the indirect joints. The results showed that if shear displacement between a steel brace and existing concrete of indirect joints in external seismic retrofit method is not large enough, there is a high probability that the anchors used in the indirect joints will be unable to exert their full shear force. They also showed that before shear slip on contact surfaces of the indirect joints occurrs, the bond resistance of the contact surfaces controls the behavior of the joints, and after that the frictional resistance of the contact surfaces and the shear resistance of the anchors control the behavior of the joints.

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