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International Concrete Abstracts Portal

Showing 1-5 of 12 Abstracts search results

Document: 

SP112-05

Date: 

January 1, 1989

Author(s):

A. K. Maji and S.P. Shah

Publication:

Symposium Papers

Volume:

112

Abstract:

The fracture process of a composite material involves crushing or slippage of adjacent particles, microcracking, etc., resulting in changes in the load-versus-displacement behavior. A study of the fracture process is necessary to develop a rational material model. Laser holographic interferometry was applied to study the whole field deformation pattern. Speckle photography was used to measure quantitatively displacement discontinuities at bond cracks at various stages of loading. Acoustic emission (AE) techniques were applied to monitor microseismic activities resulting from the various fracture phenomena. The rate of microfracture was measured from the AE event rates. A source location algorithm was used to calculate the locations of the AE events. Specimens were made with different aggregate and void sizes to study their effect on crack patterns and load-displacement behaviors.

DOI:

10.14359/2846

Document: 

SP112-04

Date: 

January 1, 1989

Author(s):

M. Ohtsu

Publication:

Symposium Papers

Volume:

112

Abstract:

On the basis of the acoustic emission (AE) measuring technique, a diagnostic method for nondestructive evaluation of cracks in concrete is proposed. The diagnostics consist of a mechanical criterion of crack initiation, a quantitative waveform analysis of AE, the evaluation of deterioration by a test of core specimens, and the ultrasonic spectroscopic investigation of cracked members. Results of basic studies on these methods are summarized. Results of basic studies confirm the feasibility and the usefulness of the proposed method as diagnostics of cracks in concrete structures.

DOI:

10.14359/2840

Document: 

SP112-02

Date: 

January 1, 1989

Author(s):

A. Alexander and H. T. Thornton

Publication:

Symposium Papers

Volume:

112

Abstract:

A new improved prototype ultrasonic pitch-catch (two-transducer) and pulse echo (one-transducer) system has been developed for concrete. Signal generation and detection is done with piezoelectric crystals. A literature search revealed that no piezoelectric pulse-echo system had been developed for the ultrasonic range ( > 20 kHz) and that pitch-catch measurements needed further development. No commercial system could be found on the market for making pitch-catch measurements. Research by the U.S. Army Engineer Waterways Experiment Station has resulted in the development of a 200-kHz pitch-catch system with a signal-to-noise ratio of 18 and a pulse-echo system with a SNR of 8. The mass and dimensions of the improved system have been reduced significantly from the prior state-of-the-art system. The WES system works well for thickness measurements of portland-cement concrete pavement and can indicate the presence of voids.

DOI:

10.14359/3655

Document: 

SP112-11

Date: 

January 1, 1989

Author(s):

R. L. Dilly and W. L. Vogt

Publication:

Symposium Papers

Volume:

112

Abstract:

Pullout testing and maturity have practical construction applications. Maturity is used to determine curing duration. The pullout test is used to determine in-place strength and to verify the adequacy of cure. Personal computers with spreadsheet software are tools that can benefit concrete construction. Templates developed using spreadsheet software can be used to acquire and analyze relationships between in-place strength and compressive strength, and maturity. Experimental investigations using pullout testing and maturity were undertaken and are reported using graphic features of spreadsheet software. The results of these experimental investigations show that curing environment can affect in-place strength relationships. Also, the results show that top to bottom strength differences can exist and should be considered when determining in-place strength. The results obtained using the compressible disk pullout assemblies indicate that this test method can be used to determine in-place strength without formwork removal, and the method should be further researched.

DOI:

10.14359/3742

Document: 

SP112-09

Date: 

January 1, 1989

Author(s):

C. J. Turkstra, P. Zoltanetzky, Jr., H. P. Lim, and C. Gordon

Publication:

Symposium Papers

Volume:

112

Abstract:

Presents a comparison of 28 day concrete strength as measured by field probe penetration tests and standard laboratory cylinders. Over a period of 11 months, 318 matched sets of tests were performed on 4000-psi concrete at four major projects. Primary field variables include the project location, operators, test guns, and the element type on which the field tests were made. Corrections to account for temperature variations are considered. Results include statistical analysis of the effects of test parameters and the correlation between field and laboratory results. Based on standard statistical tests, it is concluded that the variability of field probe results is similar to that of the corresponding laboratory cylinder tests. Results did not depend significantly on operators or the particular equipment used. However, results did depend significantly on the type of structural element tested and on the range setting of the firing gun. It is concluded that the calibration charts provided with the equipment should be reviewed.

DOI:

10.14359/3736

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