Monitoring fresh cementitious material by digital image correlation (DIC)

Abstract

Concrete undergoes strong displacements due to different processes at very early state, like shrinkage. This early state of concrete affects the long-term concrete performance. The concrete deformation cannot be directly attributed to a single process, due to the complexity of different processes such as, evaporation, water migration, settlement, formation of hydrates, shrinkage, early age cracking. Monitoring concrete properties at a very fresh state is essential to understand the different ongoing processes. Digital image correlation (DIC) has proven very useful as an optical and contactless method for surface monitoring of several materials. In the present paper the displacement distribution of fresh cementitious material from plastic state up to hardened state is studied by means of DIC. Moreover, an innovative technique of speckle pattern creation is presented, since creation of a pattern on fresh (and hence viscous) cementitious materials is not straightforward. The specimen surface is covered with a speckle pattern that deforms together with the specimen. The principle of DIC realizes a 3D continuous monitoring by recording the images at different time steps and comparing it to the reference or undeformed image. The experimental results confirmed the effectiveness and correctness of the new technique giving a global overview much more representative than point measurements with traditional displacement meters