M.R. de Rooij

Dynamic volume change measurements of cereal materials by environmental scanning electron microscopy and videomicroscopy

Moisture migration induced volume change in cereal materials was studied by environmental scanning electron microscopy, videomicroscopy and stereoscopy. It is shown that the in situ volume change can be monitored by the changes of projection area with the assumption of isotropic swelling/shrinkage. The projection area change from videomicroscopy matches well with the volume change by stereoscopy after dimensional normalization. The arbitrary volume values in between two relative humidity levels are available by interpolating the equilibrium volumes at beginning and ending. The sorption/desorption curves were fitted by the ‘parallel exponential kinetics’ model, which described two independent, parallel processes as ‘slow’ and ‘fast’. In the low relative humidity range, sorption curves match well with the ‘parallel exponential kinetics’ model and the two parallel processes tend to be identical when relative humidity increases. The diffusivity of water moisture in a cracker, which was estimated by the half‐equilibrium principle, has a strong dependence on relative humidity.

Active thin sections to study syneresis

Abstract Thin sections are made from hardened products. To achieve information on the very early hydration process of cementitious composites, one would need an “active thin section,” i.e., a thin section of a cement paste that is hardening while under investigation. In our research, it has been possible to construct such active thin sections. Using ordinary light microscopy it is possible to observe water movement and volume changes on hydrating specimens of about 100-μm thickness. This research is part of a larger project to investigate the formation of the interfacial transition zone. We believe that a process called syneresis might play an important role. Syneresis is the contraction of a gel under the expulsion of a liquid. This is addressed in the second part of this paper. This phenomenon is studied using active thin sections.

Long-term performance of marine structures in the Netherlands - validation of predictive models for chloride ingress

For many concrete infrastructural works a service life of 80, 100 or 200 years is required. To convince owners and authorities that these requirements can be met probability-based models for service life predictions have been developed. These models are based on theoretical and experimental laboratory studies. Many of these models focus on the probability of chloride-induced rebar corrosion. For a check of the reliability of one of these models, i.e. the DURACRETE model, predicted chloride profiles have been compared with chloride profiles measured in five marine concrete structures. Lessons learned from these existing structures in view of the reliability of numerical service life predictions are presented in this paper.

Dynamic volume change measurement in environmental scanning electron microscope

Moisture transport is one of the most important phenomena in organic materials in a variety of fields. As the result of this process in the fields of biology, polymer, food, and agriculture, volume change like swelling and shrinkage have received a lot of theoretical and experimental attention. However, many questions remain about the nature and behavior of moisture hydration and dehydration because of the limitations of the experimental techniques to study it. Although many methods are available to measure the static volume change both directly and indirectly when volume reaches its equilibrium, for example tilting sample stage in ESEM to make stereoscopic images, it is difficult to determine in situ the volume evolution during relative humidity (RH) changing, especially at the beginning of RH change due to the time limitation to tilt the stage without introducing additional errors. We describe here a procedure that provides a rapid way of measuring volume change as the function of relative humidity and time.