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 influence of mix constituents on the quality of concrete is discussed. Results demonstrate that the assessment of concrete performance based on the traditional parameters such as water-cement ratio and 28-day strength may be misleading. One way to insure a durable structure is to specify concrete by performance criteria. This would overcome not only the influence of constituents, but would also place emphasis on proper curing. For the protection of reinforcement against corrosion, performance criteria based on carbonation and water sorptivity are suggested.

The authors had tested eight square reinforced concrete columns subjected to combined flexure and constant axial loads of 0.254 to 0.629 f'?c A?g, and the test results were reported in a previous paper. This study is a continuation of that previous study. The objective of this study is to evaluate the ductility enhancement of high-strength concrete columns achieved by effectively confining the core concrete using transverse reinforcement with high yield strength. Four test columns were constructed using concrete with compressive strength of 130 MPa, transverse reinforcement with yield strength of 408 or 873 MPa, and ordinary longitudinal reinforcement. Those columns tested under reversed cyclic lateral loads with constant axial compressive load levels of 0.343 or 0.473. Test results indicated that even for such high-strength concrete columns adequate ductility was secured by using high-strength transverse reinforcement. Based on the test results, the stress-strain model on confined concrete previously proposed by the authors was modified to be applicable not only to ordinary strength concrete but also to high-strength concrete

The IBM tower in Singapore is a 40-story office/retail complex. The structure is V-shaped in plan up to the 16th floor, where one leg of the vee is dropped. The rhomboidal shape continues to the top. Services like emergency stairs, elevators, and mechanical rooms are located at the end of the vee, thus creating three cores at the base and two from the 17th floor up. There are no floors between the 16th and 23rd levels. The office floors from the 23rd to the 40th levels are supported on three main transfer girders at the 23rd level, spanning between the two service cores. A three-dimensional analysis was carried out for gravity and lateral loads. Transfer girders were analyzed separately using finite element techniques. Separate analysis was also performed for construction sequence loading on transfer girders. The final results in deflection matched closely with three-dimensional analysis. Severe restrictions on the deflection of transfer girders created unique design challenges.