International Concrete Abstracts Portal

This paper presents the results of investigation on a pullout technique for the determination of in-situ strength of concrete. In essence, a pullout test consists of measuring the force required to pull out a specially shaped inserts whose enlarged end has been cast into the concrete. In this investigation, pullout tests were performed on 6OO-mm cubical concrete blocks. Compression strength tests were conducted on standard 15O-mm cubes and also on 1 00 x 200-mm cores drilled from the 6OO-mm blocks. Statistical analysis of the test data shows that there is a good correlation between the pullout strength and the corresponding compressive strength of cubes and cores. The test is simple, inexpensive, effective and has an acceptable degree of reproducibility. It has the potential to be a useful additional tool for in-situ quality control of concrete.

This paper reports on an investigation undertaken to determine the within-test variability at the ages of 1 to 3 days of various in-situ tests cur-rently being used in the field, and to determine their ability to predict early-age strength development of concrete for formwork removal purposes. The methods investigated included penetration resistance, pulse velocity, rebound number and two types of pullout tests. The tests were performed at 1, 2 and 3 days on plain concrete slabs, 300 x 1220 x 1220 mm in size. I The test results indicate that the pulse velocity method had the least variability with a within-test coefficient of variation of less than 0.5% whereas the rebound method had the highest variability with anaverage coefficient of variation in the order of 12%. The values for other in-situ tests ranged from 5 to 10%. It is concluded that all in-situ tests, with the exception of the rebound method, can predict the early-age strength development of concrete within a reasonable degree of accuracy, and thus can be applied to determine 5 safe stripping times for removal of formwork in concrete construction.

The standard method of determining the quality of hardened concrete is the cylinder test. Unliess test results fail to meet specified values, and other test procedures are called into play, the standard cylinder test is usually the only quantitative measure of the quality of concrete in a structure. Analysis of test results to ACI 214 enables assessments of this quality to be made. On two large projects in Toronto, horizontal elements were extensively test4d by in-place testing for form removal, termination of shring, and confirmation of specified 28-day strength. Permission to waive standard cylinder testing for these elemnets was obtained from trhe City Building Department. Out of interest the cylinders were made and tested. It is therefore possible to evaluate the quality of the concrete on these projects by both the standard procedure, and by in-place testing. This is addressed in this paper together with a discussion of statistical evaluation of in-place test data.

The determination of concrete properties using theoretical and/or empirical relationships is commonly used in the design and construction of concrete structures. It is argued that, at best, all such estimates could only be approximate, given the varied nature of concrete due to its intrinsic make-up and work-manship, as well as such factors as environmental conditions and age. The use of non-destructive testing of concrete should be assessed against this background. The current position on the testing of in-situ concrete is briefly reviewed and the potential application of the non-destructive tests discussed. A method combining the rebound hammer and pulse velocity readings is explained. Both tests are very simple and rapid to perform and from the studies undertaken in Australia and Scotland it would appear that the combined method approach could help to further increase the confidence in estimating the strength of in-situ concrete.

The purpose of the present paper is to obtain a practical expression for estimating the compressive strength of concrete the nondestructive testing method combining rebound number evaluation of the -I L L .n strength of concrete members or structures. with ultrasonic pulse velocity and to discuss its applicability to Experimental investigations were carried out to examine the effects of factors such as water-cement ratio, the maximum size and volume fraction of coarse aggregate, the curing condition and age of concrete. Accuracies of the prediction expressed in concrete strength are proposed. The equations are applied for empirical formulae are examined by multiple and practical equations for estimating the evaluating the-strength distribution in a concrete column and in an existing concrete building.