International Concrete Abstracts Portal

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

Rheological properties of fresh concrete are important both for the requirements for various production methods and for designing the desirable properties for a particular concrete. The research reported in this paper provides more basic information about factors controlling rheological properties of concrete. The results of the traditional slump test and Tattersall's approach (two-point test) are discussed. The relationship between paste and concrete rheological properties is evaluated. Rheological properties can play an important role in improving the engineering properties of concrete and provide valuable information for design innovations.

In repairing cracked concrete structures, excellent workability and repairing effects have been obtained by using epoxy resins that are liquid organic polymer materials. However, in most situations, the repairing effects are not long-term and when these organic materials are used and exposed outside for a few years, they will deteriorate. Therefore, a material for crack injection, utilizing inorganic material such as ultra-fine slag cement, has been developed recently, and has shown good performance in terms of workability and durability. In this study, plain concrete beams and reinforced concrete beams repaired by using epoxy resin or ultra-fine slag cement are tested. The results show that the repairing effect deteriorates because of bleeding or drying shrinkage when inorganic material is used with a great deal of water. However, satisfactory properties are obtained using superplasticizer added to the inorganic repair material.

Concrete is a characteristically porous material, and whatever improvements are made in its formulation and fabrication, micropores and microvoids would always exist on their surfaces. These defects encourage the transport of aggressive agents into the body of concrete, bearing in mind that cracking, depth, and quality of cover concrete and the overall quality of concrete are the three factors that influence the penetration of these agents. Surface coatings on concrete have an important role in preserving the durability of concrete and the steel embedded in it. This paper presents test data on an acrylic-based highly elastic surface coating. The strength and elasticity of the coating, its ability to bridge cracks under static and dynamic loadings, its resistance to natural weathering, heat, oxidation, sunshine, and rain are discussed. Data are also presented on the adhesion strength of the coating to concrete substrate and its resistance to carbonation and chloride penetration. Both short- and long-term test data are presented. It is shown that a highly elastic rubber coating can provide long-term durability and stability to concrete structures, and that it can maintain its integrity, continuity, and adhesion to concrete under very aggressive environmental conditions.

Steel reinforcement embedded in concrete is normally passivated in its alkaline environment. In the presence of chlorides, however, the passivating layer is destroyed and the reinforcing bar corrodes, leading to concrete cracking and spalling. Several concrete rehabilitation techniques are available, of which only the cathodic protection (CP) of reinforcing bars was found to stop corrosion regardless of the chloride content of concrete. The CP system consists of reinforcing bars (cathode) connected to the negative terminal of a DC power supply, the positive output of which goes to an anode usually embedded in concrete. This paper describes some properties and applications of a proprietary activated titanium anode mesh and ribbon to a variety of old and new concrete structures: bridges, tunnels, buildings, wharves, piers, offshore platforms. Since its commercial introduction in 1985, 290,000 mý of this anode mesh has been or is being installed all over the world, whereas from 1987 the anode ribbon has been or is being applied to 29,000 mý of concrete surface. The paper addresses also the design and various installation techniques of anodes, as well as the testing, commissioning, and cost of the CP system.