Anomalies of Shrinkage and Tensile Creep of Concrete

Experiments have shown that shrinkage of concrete is larger in those specimens which are loaded in tension compared to non-loaded specimens. The hypothesis is that this is a consequence of microcracking and increase of water diffusivity. Water diffusivity is indeed increased by tensile loading as several researchers have demonstrated. That shrinkage is increased by tensile loading is in contradiction to other theories which state that surface cracking is caused by eigenstresses during drying and thus the shrinkage strain is reduced. Several experimental series have been carried out on concretes with various strength and composition which have confirmed the phenomenon. Another phenomenon has been observed on concrete which was mixed with superabsorbent polymers (SAP). Superabsorbent polymers are a new class of admixture. They absorb a manifold of water compared to the own weight. Mixed in concrete, they store the water and release it during the hydration of cement. They can be used for internal curing of high-performance concrete, further, they can heal cracks and can make concrete more impervious. Tensile creep tests have been performed on dogbone shaped specimens. It appeared that tensile creep of SAP modified concrete was considerably reduced while shrinkage was not. The reason for this behavior is attributed to self-healing of microcracks. Results will be shown and discussed.