AFM AND SEM STUDIES OF C-S-H GROWTH ON C_3S SURFACE DURING EARLY HYDRATION

摘要

The C-S-H formation, responsible for setting of cement, has been studied during early hydration of C_3S. Experimental kinetics studies during this period tend to prove that C-S-H nuclei grow parallel and perpendicular to the surface of C_3S grains with different rate depending on the lime concentration in solution. Numerical simulations of the C-S-H growth based on the aggregation of small elements around C-S-H nuclei on a flat surface well account for the experimental kinetics results. Direct observation of the hydration process at the interface C_3S-solution which were performed by Atomic Force Microscopy in a wet cell validate this model. The covering of a flat alite surface is observed as made by oriented aggregation of small elements of 60~*30~*5 nm with the most developed face parallel to the surface. The direct measure of the ratio between the growth parallel to the surface of C_3S and the growth perpendicular to the same surface is in accordance with the simulation of experimental results. High Resolution Scanning Electron Microscopy observations (magnification from 20 000 to 430 000) enables to observe actual C_3S grains hydrated at different percentages of reaction. The agglomeration of same elementary C-S-H particles (with almost the same size) have been observed with SEM at very low percentage of reaction but the dehydration under vacuum and sputtering conditions modify the sample altering C-S-H particles contrary to AFM.