Microscopic Studies of the Early Hydration of Calcium Aluminate Cements

摘要

Three complimentary microscopy techniques have been used to characterise the early stages of hydration of calcium aluminate cements (CACs). In particular the study has focused on the amorphous products which form before the massive precipitation of hydrates at the end of the induction period. Analytical Transmission Electron Microscopy was used to characterise the products after drying and shows them to be rich in alumina. Atomic Force Microscopy provided high-resolution images of the same gel, showing its colloidal structure. Finally, x-ray transmission microscopy allowed the cement paste to be observed in the wet state over time as the chemical reaction occurs. The x-ray images show that the formation of CAC hydrates takes place by a dissolution-precipitation process. The amorphous products form quickly after the addition of water in two locations, in the solution and around the anhydrous cement grains. A thickening of the layer around anhydrous grains is observed over time.