ABSTRACT
In order to quantity resistance to cracking due restrained shrinkage, ring tests were used according to the ASTM C1581-04 standard. Two specimens with a 38 mm thickness, 330 mm inner diameter and 152 mm height were cast around the steel ring. After the pouring, the specimens were immediately cured at 20°C and 50% R.H. The restrained shrinkage of the mortar composite caused compressive strain to develop in the steel ring. This last is measured by two strain gages bonded to the inner surface. The day of the crack initiation was determined thanks to the stress relaxation induced in the steel ring and the resulting sharp drop in the confining strain-time curve. After the cracking of the mortar, the crack width was monitored by a video-microscope with the maximum enlargement of ×175. Figure 1 shows a crack through the entire height of a specimen type 0R0F.
