Study of ‘real’ shrinkage by ESEM observations and digital image analysis

Defining the 'real' shrinkage values of concrete is still a subject of much debate. In shrinkage experiments size effects are inherently present. Through an attempt to determine the real shrinkage of cement-based materials, these size effects have to be eliminated or at least reduced as much a possible. In this contribution drying shrinkage experiments on thin cement paste samples are discussed. Thin-cast Portland cement paste specimens (2 mm) are used, polished to 1 mm with specially designed tools. Samples with and without aggregate inclusions (glass pearls) are considered. The specimens are dried in Environmental Scanning Electron Microscope (ESEM) from 100% to 20% relative humidity (RH). ESEM images are acquired during drying and analyzed by means of Digital Image Analysis. Both drying shrinkage and microcracking are determined. The analyses show a non-linear relation between RH and shrinkage deformations in the whole drying range (from 100% to 20%).Structural EngineeringCivil Engineering and Geoscience