Identification of microcracks caused by autogenous shrinkage

Detection and quantification of microcracks caused by restrained autogenous shrinkage in high-performance concrete is difficult. Available techniques either lack the required resolution or may cause further cracks indistinguishable from the original ones. The new technique presented in this paper allows detection of microcracks while avoiding artifacts induced by unwanted restraint, drying or temperature variations. The technique consists of casting small circular cylindrical samples of cement pastes in silicone moulds. Steel rods of different diameters are cast into the cement paste to restrain the autogenous shrinkage and cause crack formation during hardening. Subsequently, liquid gallium is intruded into the cracks under pressure. After solidification of the gallium, the crack pattern is frozen and can be analyzed after plane polishing of the samples. The microcracks are identified by optical microscopy, electron probe micro analysis, EPMA, and scanning electron microscopy, SEM. A preliminary analysis of the observed microcracks is presented in this paper.