Study of Creep in Concrete - Phase 2 (Hollowbox Beam)

摘要

Cylindrical concrete specimens 3 inches in diameter by 9 inches long and 6 inches in diameter by 18 inches long were tested in controlled storage environments of 20% RH, 50% RH, 75% RH, and 100% RH, with the temperature at 73 F in all cases. Creep specimens were subjected to constant sustained compressive loads causing stresses up to about 50% of the ultimate compressive strength of the concrete. Nonloaded companion specimens were included to determine shrinkage. Time-dependent strain measured on a loaded specimen (total creep) is shown to be the result of viscous flow (viscous creep) and of seepage of gel water (seepage creep). Total creep data from the cylinders were extrapolated to estimate the total creep of beams by plotting these data versus the ratio of the exposed surface area to volume. Errors in the estimates were determined from previous data obtained in hollow-box beam tests. For the top of the hollow-box beams, they were as follows: +8.8% near the center and +9.5% near one end (175 days after loading); +0.6% near the center and +4.8% near one end (897 days after loading); -1.8% near the center and +3.2% near one end (using maximum strain attained in the beams). (Author)