Results of tests carried out to investigate the causes of early-age cracking reported in some precast, prestressed, steam-cured structural members are reported. Cracks have been observed at the fabrication site even before structures are put into use. An investigationwas conducted into the development of concrete physical properties at early ages when the concrete is steam cured. Properties investigated were compressive strength, elastic modulus, splitting tensile strength, and poisson's ratio. A prestressed concrete producer sample was used in the fabrication of conventional 6- x 12-in. Cylinder test specimens. Test results were obtained for 8 hr, 14 hr, 1 day, 2 days, 3 days, 7 days, and 28 days. Tests were carried out on both steam-cured and companion standard moist-cured specimens for coparison.Steam curing was found to be beneficial to the development of all the physical properties only at early ages. The beneficial effect wasfound to be the least lasting on the tensile strength development in which the benefit appeared to have ceased even before steam curingwas discontinued. This resulted in lower tensile strength value forthe steam-cured specimens when compared with the values for their standard moist-cured companions. The observed low tensile strength developed in steam-cured specimens may be responsible, at least partially, for the cracking reported during strand release and form stripping at prestressing plants. This paper appears in transportation research record no. 1284, Cement, admixtures, and concrete 1990.
Samenvatting