Stresses and creep relaxation induced in restrained autogenous shrinkage of high-strength pastes and concretes

The development of internal stresses induced by restrained autogenous shrinkage in cement pastes and concretes with low water/binder ratios was investigated. The restrained autogenous stress developed was smaller than that expected on the basis of consideration of the autogenous shrinkage strain only. This was accounted for by relaxation due to early age creep. Reduction of w/b and the addition of silica fume led to stresses that could approach 50% of the strength. At such high stresses, the risk of cracking was significant. Development of the stress in high-strength concrete could not be directly related to the properties of its cement paste matrix. The presence of aggregates reduced proportionally the autogenous shrinkage. However, this was not accompanied by a similar proportional reduction in the induced stress, since the aggregate also caused a reduction in the creep relaxation effect. The reduced creep in the concrete, compared with the paste, was not always proportional to the aggregate content.