In Situ Tests: Variability and Strength Prediction of Concrete at Early Ages


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Title: In Situ Tests: Variability and Strength Prediction of Concrete at Early Ages

Author(s): G.G. Carette and V.M. Malhotra

Publication: Special Publication

Volume: 82


Appears on pages(s): 111-142

Keywords: age-strength relation; cores; form removal; fresh concre nondestructive tests; penetration tests; variability. compressive strength; concrete tes; impact hammer tests; tests; pullout tests; ultrasonic

Date: 9/1/1984

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.