International Concrete Abstracts Portal

ACI Committee 228 has been active in the field experiences in the area of nondestructive testing of concrete. This volume contains 16 papers of which many were presented at the two most recent technical sessions organized by the committee. The first session was held during the ACI Spring Convention in 1993 in Vancouver, BC, Canada. The second session was held during the American Concrete Institute Fall Convention in 1995 in Montreal, Quebec, Canada. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP168

Experimental work has been undertaken in the laboratory and on site to assist understanding and interpretation of the results of radar testing of structural concrete. This has included the development and use of a large-scale emulsion simulation tank in which a very large range of reinforcing steel and void configurations have been examined with field testing apparatus for a range of simulated concrete properties. A library of characteristic responses as well as limits of size and spacing upon successful resolution have been obtained. A large diameter co-axial transmission line has also been designed, fabricated and used to determine the fundamental electrical properties of a range of concretes and moisture conditions at frequencies from 1 MHz up to 1 GHz. Results have been compared with those for tests on larger concrete specimens with field testing apparatus and confirm the dominant influence of moisture compared with other aspects of the concrete composition. Frequency effects are quantified and related to characteristics of field antennas, and potential errors of using ‘typical’ values of concrete properties in interpretation and numerical modelling are identified. The test results from transmission line studies are compared with experimental and theoretical results from other research workers.

In the past few years, a great progress was done in the field of acoustical imaging. One aspect of this progress has been the application of this evolving technique to the non-destructive evaluation of civil engineering structures. This paper gives a brief review of the basic theory of acoustical imaging. It also describes a case study to highlight the practical aspects and the possibility of using this technique to assess the internal conditions of concrete structures.

This paper describes the application of geophysical tomography and scientific visualization techniques for evaluating the internal condition of massive concrete structures. The resulting output is a three dimensional representation of the structure showing the spatial distribution of ultrasound data. As various aspects of ultrasound data (e.g. velocity and attenuation) are related to concrete quality, the location and orientation of areas of inferior material or discontinties can be identified. In addition, specific features within the image can be highlighted and quantified. Results are presented from a preliminary study carried out to assess the potential application of this technique for evtiating the internal condition of large concrete elements. A large concrete block was constructed with a number of internal defects such as cracks, areas of poorly compacted concrete and uncemented aggregate, and large voids. A large number of measurements (ultrasonic pulse velocity) were taken to provide a network of velocities across a section. Algebraic tomographic techniques were then applied to reconstruct a two dimensional image. By taking a series of contiguous sections and stacking them together, a three dimensional model of the sample or structure was then created. Finally the three dimensional data set was visualized using advanced graphics techniques such as vohune rendering. Overall, the initial results are promising, and indicate that the presence and location of internal defects can be determined

The resistance of concretes to the transport of chloride ions is defined generally by the coefficient of diffusion. This, combined with a knowledge of the exposure of concrete to chlorides, can be used to estimate the depth of penetration of chlorides over a period of time. Therefore, an indication as to the likelihood of chlorides reaching reinforcement can be determined, and, if there is a risk of corrosion, preventive measures can be taken. The procedure to find the coefficient of diffusion from a standard diffusion test is well established. However, such a test may need several months to finish, depending on the quality of the concrete and the thickness of sample tested. As a consequence this is not a practicalmethod, and different organisations have conducted research to determine the coefficient of diffusion (D) more rapidly. The approach adopted has been to force chlorides through the test sample by applying a voltage, and such tests are known as accelerated chloride migration tests. By using this principle, and following from early studies by Whiting, a new test method for determining the chloride migration coefficient of the near surface concrete in-situ is being developed at Queen’s. This test makes use of a set up similar to the well established Autoclam permeability system. The results of an investigation carried out with this new apparatus is presented in this paper along with a description of the new test method. Early results indicated that this new test method could form the basis to determine the chloride diffusivity of the near surface concrete on site.