A rheometric approach to assess plastic shrinkage and implications of early age drying on the microstructure of cement-based materials

3D printed cementitious materials are subjected to environmental drying from a very early age as it does not have any formwork protection. In this paper, we present a novel methodology using a rheometer for measuring the shrinkage strains in such stiff cement-based materials from the onset of processing. In this approach, cylindrical samples are placed between parallel plates attached to the rheometer and continuous monitoring of shrinkage strain is made possible by using a constant normal force protocol. Using this protocol, shrinkage strain was measured in samples subjected to external drying and protected from drying and also on samples with and without shrinkage reducing agent. It was found that the incorporation of about 3 wt% shrinkage reducing agent significantly reduces the early-age shrinkage strain. The effect of early-age drying induced microstructural changes was investigated in this study using mercury intrusion porosimetry, loss on ignition and electrical resistivity measurements. When subjected to early age drying, the porosity of the samples was found to increase significantly and the assessment of chemically bound water revealed that the degree of hydration was not uniform, but varied as a gradient with the minimal values at the drying surface.