FREE AND RESTRAINED SHRINKAGE OF NORMAL AND HIGH-STRENGTH CONCRETES

Free and restrained shrinkage of concretes with and without silica fume were studied. A special uniaxial restraining rig was developed in which the stress required to prevent shrinkage from occurring could be monitored. Variables studied were the water-cement ratio (w/c), influence of silica fume, and exposure conditions (either exposure to drying environment immediately after casting or immediate sealing of the concrete after casting). The presence of silica fume increased free plastic shrinkage of the concrete and led to earlier cracking than a similar low-w/c concrete (0.33) with no silica fume. The sealed low water-binder ratio (w/b) concretes (0.33) developed considerable restraining (residual) stress, but none of them cracked. This stress was higher in the silica fume concrete.