Title: Contract Strength Requirements-Cores
Versus In Situ Evaluation
Author(s): V. M. Malhotra
Publication: Journal Proceedings
Appears on pages(s): 163-172
Keywords: accelerated tests;acceptability;building codes;compression tests; compressive strength;curing; cylinders; field tests;fresh concretes;hardened con-cretes; concrete cores;nondestructive tests;penetration tests;pullout tests;quality control.
The present day building codes allow acceptance of concrete on the basis of the 28-day compressive strength of test specimens cured under standard conditions. If test cylinders fail to reach the criterion specified in the codes, drilling and testing of cores is required as the codes permit no other method of evaluation. This paper discusses the problems associated with evaluation of core test data and emphasizes the contradictory nature of the available information. The effects of the variables such as length-depth ratio, embedded reinforcement, type of aggregate, strength level of concrete, direction of drilling, and curing of concrete are discussed. The unsatisfactory nature of the existing acceptance procedure is brought out and a case is made for the abandonment of the existing acceptance procedure in favor of a new approach. The suggested procedure consists of three steps: First, it is insured that concrete delivered to the site meets specification requirements. Second, accelerated strength testing is employed for acceptance testing. Third, emphasis is placed on in situ testing of hardened concrete using such methods as the pullout, penetration resistance, hardness, and pulse velocity.