Creep of high–strength concrete and normal–strength concrete

The development and use of high–strength concrete has been evolutionary. High–strength concrete is used for tall buildings, bridges, long–span structures and offshore platforms. Very little information is available on the creep of high–strength concrete compared with that of normal concrete at room and low temperatures. Test results are presented of creep strains at room temperature of high–strength concrete (70 Mpa) and normal concrete (40 MPa) subjected to stresses of 25, 50 and 75% of their 28 day strength for one year. Also provided are creep results of test specimens exposed to temperatures of 20, 0 and — 10°C for 91 days. In general, creep strains of high–strength concrete are smaller than those of normal concrete at all corresponding stress/strength ratios. The relation of creep to stress–strength ratio at room temperature was found to be linear for the two grades of concrete. Test results revealed that low temperatures had a minor effect on the magnitude of creep strains for both types of concrete. The creep mechanism of high–strength and normal concrete can be explained mainly by the diffusion of absorbed moisture, while at low temperatures both the gel deformation and absorbed moisture diffusion can cause a large change in the energy of the system, and accordingly creep strains were slightly increased.