International Concrete Abstracts Portal

This paper summarizes recent developments in the impact-echo technique for locating defects in concrete structures. First, the impact-echo principle is reviewed and frequency analysis of impact-echo signals is explained for those unfamiliar with the technique. Advancements in signal processing that have been aimed at simplifying and automating data interpretation are discussed, and examples from the use of an artificial-intelligence technique for automated interpretation of signals from plate-like structures are shown. Impact-echo instrumentation is reviewed and an impact-echo field system is described. The newest application for the method is testing bar-like structures, such as columns and beams. Numerical and experimental controlled-flaw studies established the basis for the use of impact-echo for this application. Representative results obtained from impact-echo studies carried out on reinforced concrete columns with circular and rectangular cross sections are presented. Finally, an overview of ongoing research is presented.

A research program was undertaken to evaluate commercially available nondestructive testing techniques to locate voids in grouted tendon ducts. A laboratory scale mockup was used to evaluate several methods. On the basis of these results, impact-echo, ultrasonic, pulse-echo, and ultrasonic pitch-catch systems were selected for further evaluation. A full-scale mockup of a section representing an icewall of an offshore drilling structure was fabricated. It contained grouted tendon ducts with voids of various sizes and configuration. A test was carried out in which three teams of researchers from Canada and the U.S. evaluated nondestructively the mockup without knowledge of the locations or nature of the voids. This paper presents the results of the preceding evaluation and makes recommendations for further research.

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 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.

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.