International Concrete Abstracts Portal

An investigation was carried out to evaluate the effectiveness of epoxy systems injected into cracks in concrete in order to repair damaged concrete structures. It was found that the usual parameters (viscosity, elastic modulus) characterizing epoxy system are not sufficient for such an evaluation, since concrete microstructure and crack width are determinant factors. Successful1 injection into larger macrocracks (>0,8 mm) is independent of the epoxy system viscosity. However, for narrower cracks (< O,3 mm), the effectiveness of the injection strongly depends on the viscosity of the epoxy system, so that a threshold value of viscosity can be determined for each microcrack width. The injection of epoxy systems into cracks of porous concretes causes, in addition to the crack filling, an impregnation of the material surrounding the crack area. This impregnation causes a strength increase, which is higher for more porous concretes and higher epoxy system viscosity. The mechanical behaviour of injected concretes do not depend significantly on the mechanical properties of the epoxy system, whereas the rheological properties of the epoxy system can affect the performances of injected concretes.

Recently, the quality of the surface layer of concrete has been recognized as an important index to relate the durability of concrete structures. However, an appropriate assessing method has not yet been achieved. The assessment of the change in the quality of the surface layer should be made from the viewpoint of not only the mechanical property but also other physical and chemical properties, such as pore structure, carbonation and so on. Attaching importance to the simplicity of tests on site, the authors have proposed that the pull-off tensile strength by the pull-off method is applicable to the former and the recovering speed in the rapid air permeability test to the latter. This study describes the results of tests on the surface layer of concrete using specimens exposed in both inland and seashore locations in the cold district of Japan. Then, the capabilities of two specific tests are examined to assess the properties of the surface layer of concrete due to weathering and other environmental attacks.

SP128 Leading world experts met in Hong Kong to participate in The ACI conference on Evaluation and Rehabilitation of Concrete Structures and Innovations and Design. The specific purpose of the Conference was to disseminate technical information on emerging concrete technology in the Pacific rim region. You can review the results of that timely event in a two volume document comprised of 90 technical papers. Volume I contains paper dealing with materials. Topics include: high elastic surface coatings, concrete deterioration on high chloride and sulfate environment, nondestructive testing, impact-echo technique, fiber reinforcement, injectable cementitious materials, and case studies. Volume II is comprised of papers pertaining to design aspects. Topics include: concrete for offshore structures, performance of structural repairs, design of high-strength and reinforced concrete structures, design of beams and columns, and case studies.order.

A detailed investigation was made to study the shear transfer between precast prestressed beams and in situ concrete in a relatively new method of construction of continuous bridge decks where the ends of precast beams are connected to an integral in situ crosshead away from the supports. The main advantages of this method are: Increasing the span length, standardization of the beams, elimination of the deep support girder, obtaining full continuity for the dead and live loads, and possibility for using straight beams in skew and curved bridges. The prestressed beam used in the investigation was an inverted T-section, and it was concluded that: 1) The shear force is transferred from a small length at the end of the beam. 2) The in situ concrete nibs can take this shear force without stirrups. 3) There is no need either to project all the bars into the in situ concrete or to prestress the connection transversely. 4) The shape of top flanges of the prestressed beam had a significant effect on the shear transfer capacity of the connection. 5) For the beams without top flanges, the shear strength of the connection can be modified by using transverse prestressing, web shear connectors, or projection of the bars.

The wind tunnel tests were carried out on rigid models of tall buildings with square plan shape to study the effects of interference on wind loads on tall buildings. This paper presents the results of the same. Effects of various geometric and flow parameters on total force and moments are reported, which are deduced from the wind pressure values obtained on isolated instrumented buildings in the vicinity.