International Concrete Abstracts Portal

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.

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.

Provides background information related to the feasibility of offshore concrete structures for the development of hydrocarbon resources in both newly developing regions of the world and in areas of existing offshore operations where concrete is currently not used. Bottom-founded structures, floating structures, and other more specialized structures are described and their market potential discussed. Three hundred offshore platforms are planned for Asia and Australia between 1990 and 1995; many of these could be built with concrete. The use of local concrete materials and labor to produce moderate strength concrete for these platforms is discussed. Special design and safety considerations are noted. The structures can be built in dry docks, on skidways, or on submersible barges. Portions of the structures can be precast concrete. All of these structures involve some marine operations. General cost considerations and life-cycle costs are discussed.

According to the trade literature, the determinations of location, direction, and the cover thickness over a single steel bar in concrete are relatively easy and reliable from a magnetic measurement if the bar diameter is known. The estimation of the bar diameter is also possible if the cover thickness is known, although these results are less reliable. Only recent publications suggest double measurements from which both the cover thickness and the bar diameter can be estimated without previous knowledge of either of them. Unfortunately, the accuracy of diameter determination remains unimproved even with these methods. This paper attempts to present the further improvement of the magnetic determination of bar characteristics. The basic idea is to combine a magnetic device with a computer that calculates, without any previous knowledge about the bar: 1) the thickness of the concrete cover above the bar and, 2) the diameter of the bar. Preliminary data also indicate that distinction can be made whether the tested area is above a single bar or multiple bars, although this is not discussed in this paper. Experimental data obtained on laboratory specimens illustrate the new method.

Presents the results of radar tests conducted in a controlled laboratory environment to provide an independent assessment of the usefulness of the technique for investigating in situ concrete structures. Parameters studied include size and thickness of concrete elements, the presence of voids and steel reinforcement, and the influence of moisture. The use of a commercially available computerized signal enhancement system has also been examined to assess the potential benefits. Results are presented that include typical signal response traces and show the degree of precision that can reasonably be expected from radar measurements under a range of practical circumstances. Results are considered in the light of the basic theoretical factors and a number of important limitations are identified. It is concluded that the method offers considerable potential in a range of structural applications but is subject to a number of practical limitations, and guidance is offered concerning experimental technique and interpretation of results.