International Concrete Abstracts Portal

SP112 Nondestructive Testing of Concrete has been especially prepared to present, examine, and promote the use of nondestructive testing techniques in concrete construction. Providing the latest information on the development and applications of nondestructive testing techniques, this collection of 11 papers will be of interest to anyone working in the field of concrete.

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.

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.

Presents an investigation to determine the within-test variability of various nondestructive test methods (NDT) and the correlation between NDT test results and the corresponding compressive strength of cores. The size effects of coarse aggregate on the variability and correlation were also evaluated. The NDT test methods evaluated in the test series include rebound hammer, pulse velocity, probe penetration, pullout, and CAPO (cut and pullout). Companion tests of field-cured standard cylinders and cores were also made at the ages when the NDT tests were made. Results show that the within-test variability of the in situ tests reported (except the pulse velocity test) is two to five times higher than that of the corresponding standard compression test and is affected significantly by the amount of coarse aggregate and its size. There is a good relationship between the results of in situ tests and the compressive strength. In general, the highest degree of correlation is for the pullout test followed by that for the CAPO (cut and pullout) test and rebound test, probe penetration test, and pulse velocity test.

Aim is to analyze the correlations between several nondestructive measured values (ultrasonic velocity and attenuation, rebound number) and the compressive strength of concrete. A computational program performs a step-by-step analysis. First, isolated linear correlations are established for each one of the three nondestructive tests. Then the results are compared with each other in the sense of a general multiple correlation of the values. Since the results obtained from the nondestructive tests are equally scattered, the program determines interactively, in a second step, the multiple coefficients of correlation and restarts the analysis several times by tentatively disregarding the presumably bad experimental results. Since the measured values also comprise a large spectrum of magnitude, limits of validity of the assumed correlations are investigated concomitantly with the process of analysis. A last step is performed to identify a tendency of deviation of the single and multiple correlations from the basic linear ones.