Temporal and spatial development of drying shrinkage cracking in cement-based materials

In optical microscopy and acoustic emission (AE) experiments, the development in time and space of drying shrinkage cracks in hardened cement paste and a cement composite containing mono-sized glass particles has been studied. The results indicate two types of restraint, i.e. self-restraint of the specimen/structure, and aggregate restraint. In plain cement paste cracks initially develop perpendicular to the drying surface, but may subsequently grow parallel to the drying surfaces. In composites containing glass particles, aggregate restraint causes continuous growth of microcracks. AE monitoring has revealed that drying shrinkage cracks develop almost instantaneously at the onset of drying. Several AE parameters elucidate the details of the process. The two techniques are complementary: AE monitoring is suitable for temporal development assessment, whereas optical microscopy is very well suited for measuring crack geometry.