Title: Adaptation of Accelerated Strength Testing Methods for Concrete Quality Control and Quality Assurance
Author(s): Tarun R. Naik
Publication: Symposium Paper
Appears on pages(s): 39-50
Keywords: accelerated tests; compressive strength; concretes; cylin-ders;
quality control; regression analysis.
This paper presents modified boiling water methods (M.B.W. Methods) and discusses how these methods can be adapted for regular quality con-trol and quality assurance of concrete for small as well as large pro-jects. These M.B.W. Methods were found to be more suitable than other A.S.T.M. methods. Accelerated strength test data can be used in two ways: (1) for quality control, where actual accelerated strength can be used as an established target value; and, (2) for quality assurance, where, if required by the contract specification, the future strength, e.g. the 28-day strength, can be projected from the accelerated strength. In order to predict the future strength, a basic correlation curve must be established for a given set of conditions. A minimum of ten to fifteen sets of data were found to be adequate in order to es-tablish this correlation curve. The A.S.T.M. boiling water method schedule requires the strength test to be performed at 28-l/2-hour age. In order to provide the greatest flexibility in scheduling, and to eli-minate the overtime work associated with the 28-l/2-hour test, modified boiling water methods were developed in which the test is performed at either 24-hour, 28-hour, 48-hour or 72-hour age. Adaptation of these four modified boiling water methods not only eliminated overtime work required on a regular working day, but it also eliminated work on holi-days and weekends. This study showed that any one of the commergially available single use cylinder molds can be used for the M.B.W. Methods. The single use tin molds, however, were preferable. An accelerated strength testing program, along with the reliability of results obtain-ed, is discussed in detail in this paper. Some of the more important observations given in this study are: (1) overtime work can be virtu-ally eliminated by adapting the methods given; (2) influence of initial concrete temperature had minimal effect upon the accelerated strength test value; (3) a job site testing laboratory is not needed; and, (4) the danger of being exposed to steam emanating from the boiling water tank and the danger in handling boiling cylinders was ill-founded.