International Concrete Abstracts Portal

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.

Gunite (dry-mix shotcrete) was introduced to the construction industry in the early days of concrete technology (1911) when many new ideas and concepts were just developing. The literature indicates that what we know as wet-mix shotcrete had its start about the same time but did not receive positive acceptance until 1950. The evolution of the shotcrete process to its present status in the construction industry is tracked by definitions of the process from Gunite in 1912 to the American Railway Engineers Association (AREA) definitions of Shotcrete in early the 1930s. By 1951, the adopted the term shotcrete, making it the official generic name of the process. The definitions by ACI from that time on reflect the introduction of new ideas and equipment into the market place. The author questions whether some low velocity shotcretes are truly shotcrete or just an extension of the concrete pumping process. A brief description and evaluation, from the past to present, of shotcrete materials, applications, and testing is presented. The future of the process is discussed and two major problems posed: the improvement of applicator workmanship and the development of a rational design for most shotcrete applications.

The assessment of reinforcement corrosion in concrete structures before visible cracking and rust stains occur will enable the engineer to take cost-effective and timely remedial action. While half-cell potential mapping techniques have been used very successfully to indicate the location of active corrosion, this method provides no information on the severity of the corrosion rate and hence the scale of the problem. The linear polarization technique provides a means of assessing directly the rate of active corrosion by measuring the response of the reinforcement to a small perturbative signal. The method has generally been restricted to laboratory studies, due to difficulties in evaluating the region of influence of the test by allowing for a relatively high concrete resistance and in the availability of field instrumentation. This paper reports on the development of unique programmable polarization equipment, enabling corrosion rate measurements to be easily collected and stored on site. The results of laboratory studies on control specimens are compared with those taken from structures in aggressive corrosion environments. Guidance is given on the interpretation of linear polarization results from durability studies for those unfamiliar with the technique.

Corrosion of steel reinforcement in concrete is one of the major problems with respect to the durability of reinforced concrete structures. Chloride ions are considered to be the major causes of premature corrosion of steel reinforcements. A test building was constructed in 1984 and has been exposed to a marine environment under the subtropical weather of Okinawa, Japan, for 6 years. This paper presents the evaluation on this test building, where nondestructive testing has been emphasized. Using a currently developed corrosion diagnosis system, the electrochemical characteristics, such as corrosion potential, polarization resistance, and concrete resistance, are measured. These characteristics are used to evaluate corrosion of the reinforcements, and the significance of this research is to enable one to evaluate corrosion of the reinforcements more quantitatively.

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.