International Concrete Abstracts Portal

This paper describes an investigation that was carried out to determine the within-test variability of various nondestructive test methods and their correlation with the corresponding compressive strength. The nondestructive test methods that were studied were the pin penetration, the ultrasonic pulse velocity, and the nuclear density gage. The tests were performed on solid concrete blocks, cylinders, and reinforced concrete slabs at different ages. The within-test variability of the direct readings of the ultrasonic pulse velocity was small compared to the pin penetration and nuclear density gage. However, when the readings were translated into strength, the within-test variabilities of the standard compression test were about the same as the other methods. The relationship between strength and the pin penetration and pulse velocity readings were good, while the relationship between the density of fresh and hardened concrete and the nuclear gage readings were satisfactory.

Over the last 3 years, an impact-echo technique has proven to be an effective evaluation tool in identifying defects and locating embedded items in concrete structures. The advantages of the method are that it is nondestructive, relatively easy to calibrate, and testing can be conducted from one surface of the element under test. Operating experience with the impact-echo technique has shown that, within known limitations, the technique can provide a rapid nondestructive means for performing certain concrete condition surveys.

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.

During the mid-1970s, there was a boom in the construction industry in Saudi Arabia. To meet the housing requirements, and to furnish the infrastructure needed for a growing industry, construction had to be carried out at a pace unprecedented in the country's history. In the absence of guidelines, concrete specifications from other industrialized countries were used. However, when the structures started to show signs of deterioration within a short fraction of their design life, it was realized that specifications developed for temperate conditions cannot be used in this region. Field and laboratory studies carried out at King Fahd University of Petroleum and Minerals at Dhahran, Saudi Arabia, showed that concrete in this region should not only be designed for strength, but also for durability. Since permeability is one of the most important properties that control the durability of concrete, much emphasis should be given to the production of dense and impermeable concrete. This paper reports the results of an investigation carried out on a number of reinforced concrete structures exposed to underground and seawater conditions that showed serious signs of deterioration within less than 10 years after construction. The paper recommends repair procedures for the damaged structures and future practices to extend their service life.