Detection and analysis of microcracks in high-performance cementitious materials

Abstract

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 induce additional cracks. The technique presented in this paper allows identification of microcracks while avoiding artifacts induced by unwanted restraint, drying, or temperature variations. Small cylindrical samples of cement paste are cast around steel rods of different diameters. The rods restrain the autogenous shrinkage and may cause crack formation. After one month storage at 32°C, liquid gallium is intruded into the cracks under pressure and the samples are cooled. When the gallium solidifies, the crack pattern is frozen and can subsequently be analyzed by a number of techniques. A numerical analysis of the results was performed considering the mechanical properties of the cement pastes and the geometry of the samples. The experimental results and the numerical analysis showed that samples with larger steel rods (3 and 6 mm diameter) had the highest probability of developing microcracks.