Title: Optimum Steam Curing Procedure in Precasting Plants
Author(s): J. A. Hanson
Publication: Journal Proceedings
Appears on pages(s): 75-100
Describes an investigation of the effect of various steam curing procedures on the compressive strength, indirect tensile strength, and elastic properties of concrete, with particular emphasis on steaming procedures compatible with the time requirements of modern prestressing plants. In the usual operation of these plants the time lapse from casting to steam shutoff remains nearly constant at 18 hr. Consequently this investigation generally varied the delay prior to steaming from 1 to 7 hr and the steaming periods from 17 hr down to 11 hr. The rate of steam room temperature increase varied from 20 to 80 F per hr up to three maximum temperatures, 125, 150, and 175 F. The data have shown that optimum values of these characteristics are obtained with a presteaming of approxi-mately 5 hr combined with a temperature rise rate of 40 F per hr up to a constant temperature of about 150 F. A maximum temperature of 175 F provided only moderate additional benefit. This steam curing study has emphatically demonstrated the adverse effect of delays in the neighborhood of only 1 hr. If such early application of steam is required by plant procedure, the temperature rise rate should be limited to 20 F per hr or less.