Effect of autogenous deformation on the cracking risk of slag cement concretes

Autogenous deformation under restrained conditions often leads to cracking and durability problems in concrete structures. It is therefore important to monitor accurately the early age development of autogenous deformation. However, its expression depends strongly on the measuring methods and on the choice of the time-zero. In order to determine the effect of slag on the evolution of autogenous deformation, a test rig was designed to monitor this deformation for three concretes with different slag content. The choice of different time-zero was also discussed based on different methods: setting evolution, time of peak expansion and evolution of deformation rate. Moreover, their restrained shrinkage was studied by means of a Temperature Stress Testing Machine (TSTM). Following these experiments, the slag cement concretes crack later than the Portland cement concrete despite the fact that they are characterized by a larger autogenous shrinkage. This behavior is mainly due to the expansion of their cement matrix at early age and their largest capacity to relax internal stresses.