An environmental scanning electron microscope investigation of drying cement paste: Drying shrinkage, image analysis, and modeling

The Environment Scanning Electron Microscope (ESEM) and new image analysis techniques are used to document the microstructure of cement pastes. The ESEM is shown to be vital to the imaging of cement hydration products at early age. An image intensity matching technique, which computes deformation between images with a resolution of 0.1%, is used in conjunction with the ESEM. This technique is used to document drying shrinkage, which is defined as the length change associated with loss of water. The effects on drying shrinkage of w/c, curing temperature, age, and drying rate are investigated. The magnitude of shrinkage is shown to vary as a function of scale, from individual particles to an area or average behavior. Shrinkage is shown to be controlled by both microstructure and hydration product properties. W/C is shown to vary the microstructure while curing temperature, age, and drying rate affect the properties of the hydration products. Experiments and modeling shows there are restraining effects from calcium hydroxide and anhydrous cement that accounts for differences in shrinkage between single particle and average behavior. Modeling is also used to demonstrate that a cement paste shrinks more at older ages when normalized by the shrinkage of the calcium silicate hydrate and porosity. Experimental results form the basis for a more complete understanding of the (micro)structure-property relationships for cement paste.