International Concrete Abstracts Portal

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.

The use of nondestructive testing in the laboratory is well-documented and standard specifications are available. However, when these nondestructive testing methods are used on site, additional factors have to be taken into consideration to enable meaningful interpretation of measurements obtained. This aspect of knowledge has not received sufficient attention for standard specifications to be drafted. Suggestions are put forward in this paper on precautions to be taken when applying nondestructive testing on site. The methods of testing discussed include the magnetic method of concrete cover or bar size determination, the rebound hardness, ultrasonic pulse velocity and the penetration resistance (Windsor Probe) test. The methods of calibration in the laboratory are reviewed and the ways to check on equipment and its calibration during site work are proposed. The information to be recorded and the interpretation of data are discussed. The need for trained personnel to carry out site testing, as well as experienced professionals to interpret test results, is emphasized.

The pulse-echo method, the impulse-radar method, and the resonant-frequency test technique will provide accurate data relative to the physical and mechanical characteristics of in situ concrete and embedded reinforcement steel. These methods can be applied in combination or individually, dependent on the project application. Engineering data obtained from nondestructive (NDT) test procedures and enhanced by computer-analysis techniques are used in a wide variety of field inspection applications.

The half-cell potential method, one of the electrochemical techniques, is very simple and possibly the most practical method as the nondestructive inspection system for steel corrosion in concrete. However, at present, this method has been regarded as an inspection only for qualitative information on corrosion. In this study, the effectiveness of the half-cell potential method on the corrosion inspection system for steel in concrete was theoretically and experimentally analyzed, and the following results were obtained: 1) configuration of the potential distribution on the structure is more important than the value of potential itself for acquiring quantitative corrosion information on steel in concrete structures, 2) progressive corrosion area of steel reinforcement can be estimated by finding the inflection point of potential distribution curve, and 3) if the electric resistivity of concrete is measured at the same time as the potential, approximate corrosion weight loss of reinforcement can be estimated by using both the potential and this resistivity distribution data.

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.