Title: Accelerated Concrete Strength Testing at the CN Tower
Author(s): John A. Bickley
Publication: Symposium Paper
Appears on pages(s): 29-38
Keywords: accelerated tests; compressive strength; concretes; low-heat
cements; quality control; regression analysis; slipform construction;
Recognition of the advantages of being able to judge the compressive strength of concrete much sooner than by the traditional 28 day test has led to a 50 year search for reliable and convenient accelerated strength testing methods. The autogenous curing method was used as an integral part of the concrete quality assurance program during construction of the CN Communications Tower in Toronto. The results presented which are obtained from 547 sets of cylinders cast during the placing of 40,000 cu.yds. (30,580 m3) of slipformed concrete to a height of 1500 ft. (457 m) between July 1973 and February 1974 indicate that the 28 day or 90 day compressive strength of the concrete made with either low heat or normal Portland cements or a blend thereof can be accurately predicted from 2 day autogenous strength results. Accelerated strength determination played an important role in the control of quality and the overall structural safety of the concrete shaft of the world's tallest free standing structure.