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International Concrete Abstracts Portal

Showing 1-5 of 17 Abstracts search results

Document: 

SP168-08

Date: 

April 1, 1997

Author(s):

N. A. Cumming and 0. S. Ooi

Publication:

Symposium Papers

Volume:

168

Abstract:

A major structural repair and strengthening program was undertaken at a large grain shipping terminal on Canada’s northwest coast. The work was required to correct problems of excessive cracking and internal delamination in the silo walls. During the repair work, it was necessary to survey 42 silos to locate zones of delaminated or deteriorated concrete. This was done successfully using the impact-echo procedure. This paper describes the impact-echo survey and its findings. It further discusses correlation of test results to actual conditions encountered in the field.

DOI:

10.14359/5955


Document: 

SP168-05

Date: 

April 1, 1997

Author(s):

Michael E. Kalinski

Publication:

Symposium Papers

Volume:

168

Abstract:

An unidentified vehicle recently struck the bottom of a railroad overpass and damaged one of the concrete beams in the overpass. The damaged beam was taken intact to the University of Texas where the Spectral-Analysis- of-Surface-Waves (SASW) method was used to nondestructively delineate the damaged zones. SASW measurements performed on the beam revealed a significant velocity contrast between damaged and undamaged zones. These measurements were consistent with visual inspection of the beam and also indicated the presence of cracking that was not visibly detectable. In addition, SASW measurements taken while repairing the beam revealed how surface wave velocity measurements can be used to monitor improvements in the integrity of a beam after each repair step.

DOI:

10.14359/5951


Document: 

SP168-06

Date: 

April 1, 1997

Author(s):

Jiunn-Ming Lin and Mary Sansalone

Publication:

Symposium Papers

Volume:

168

Abstract:

Dilatational or P-wave speed in concrete is needed in impact-echo testing if the dimensions of structural elements or the location of flaws is to be determined. Previously the P-wave speed had to be determined from cores or from performing a test on a portion of the structure having known dimensions and no flaws. In cases where neither approach was possible, an estimate had to be made of the wave speed. This paper presents the details of a method for independently determining P-wave speed in concrete using a Rayleigh-wave speed measurement between two points on the surface. Such a procedure increases the power, versatility, and ease of use of the impact-echo method. In this paper the Rayleigh wave speed procedure is explained. Systematic errors involved in the measurement procedure areexamined, and the accuracies that can be expected using the procedure in conjunction with the impact-echo test procedure are discussed. Appropriate uses of the procedure are given, and the limitations of the method are stated. It is shown that the Rayleigh wave technique is an easy to use technique for estimating wave speeds. Typically, speeds within about 4% of the actual wave speed can be obtained.

DOI:

10.14359/5953


Document: 

SP168-12

Date: 

April 1, 1997

Author(s):

P. A. Muhammed Basheer, Peter R. V. Gilleece, Robin Andrews, and Adrian E. Long

Publication:

Symposium Papers

Volume:

168

Abstract:

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.

DOI:

10.14359/5943


Document: 

SP168-11

Date: 

April 1, 1997

Author(s):

M . Cl. A . T h o m a s , D . W i e s e , a n d H . Caratin

Publication:

Symposium Papers

Volume:

168

Abstract:

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

DOI:

10.14359/5942


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