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.

Recently, deterioration of reinforced concrete structures has been an issue of concern, such that repair methods and repair practice have been studied by many organizations. In this study the flexural behavior of FRP reinforced concrete beams (FRPC beams) was studied. The experimental values of the tensile stress in the main reinforcement, the concrete crack width, and the center displacement of FRPC beam agreed well with the calculated values. The flexural behavior of repaired reinforced concrete beams (RRC beams) using FRP and polymer mortar was studied. The results showed that tensile stress in the main reinforcement, the concrete crack width, and the center displacement of the beam were decreased after repair work. The elastic theory of reinforced concrete was still effective on the repaired beam. The values of tensile stress in the main reinforcement, and the center displacement of the beam could be calculated.

This paper deals with a new type of semiprefabricated slab. The slab is made of precast thin slab stiffened by a set of folded wire fabric including cast in-situ topping concrete. This study covers both the salient features of design and construction of this flooring system and experimental work carried out to study the flexural behavior of the slabs cast using the system. The results of the experiment showed that composite precast slab consisting of the precast thin slab and in-situ topping concrete can be designed as a monolithic component.

Concrete structures, old or new, often experience formation of cracks, even though these are accounted for by the designer at the time of construction. To repair these cracks, a large number of injectable inorganic materials (cements and cementitious grouts), organic materials (epoxies, polyurethanes, polyester, etc.) and mixtures of both have been used successfully and unsuccessfully. Cementitious materials seem to arouse great controversy among engineers, especially with regard to the acceptance levels of the consistency (water-cement ratio) to be used for injection. A hydraulic facility in Quebec is therefore evaluating a number of cementitious materials as well as various epoxies and polyurethanes for repairing its concrete structures. The paper describes the results of a study performed in the laboratory using normal portland cement (Type 10) and high early-strength cement (Type 30) both with and without superplasticizers, and two ultrafine cements, and recommends an arbitrary lower and higher limit of the water-cement ratio, which could be suitable for crack injection. It also presents some physical and mechanical data on these cements. 110-691