INFLUENCE OF PORTLAND CEMENT COMPOSITION ON ITS HYDRATION IN THE PRESENCE OF ZINC

The retarding effect of a zinc addition on the hydration of Portland cement is due to the precipitation of an amorphous layer of zinc hydroxide around the anhydrous grains. The evolution of this compound depends on different ions and their concentrations in the pore solution therefore of cement composition. The influence of sulfate proportions was studied in a previous paper. In the present one, the influence of other constituent of Portland cement is investigated. If the concentrations of calcium and hydroxide ions in the pore solution are enough, the hydration reaction starts again through the transformation of zinc hydroxide into crystalline calcium zinc hydroxide. Thus, free calcium in Portland cement is a favorable element as well as an important proportion of C3A. C4AF, C3S and minor elements have no influence on the conversion reaction of zinc hydroxide. (A) (Author/TRRL)