Lothenbach – Hydration of Blended Cements
B. Lothenbach1, E. Wieland2, R. Figi1, D. Rentsch1, B. Schwyn3
1 Empa, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Concrete & Construction Chemistry, 8600 Dübendorf, Switzerland
2 Paul Scherrer Institute, Laboratory for Waste Management, 5232 Villigen PSI, Switzerland
3 Nagra, National Cooperation for the Disposal of Radioactive Waste, 5430 Wettingen, Switzerland
The hydration of a CEM III/B and of a CEM I cement blended with silica fume was investigated experimentally. Changes in the composition of the hydrate assemblages of these cements were characterized by XRD, TGA, SEM/EDX and Si-NMR, while changes in the chemical composition of the pore solutions were determined by measuring pH and using ICP-OES and IC analysis.
In the two cements blended with silica fume a significant reduction of the pH to 12.3 and 11.3 was observed, depending on the amount of the silica fume added. After a hydration time of 1 month and longer, no portlandite could be detected in the cements. The main hydrates in both cements were C-S-H phases with a C/S ratio of about 1, ettringite and hemi- and/or monocarbonate. In the CEM III/B – silica fume mixture strongly reducing conditions were indicated by the relatively high HS– concentration in the pore solutions.
Thermodynamic modeling was used to elucidate conditions of over- or undersaturation of the pore solutions with regard to ettringite, C-S-H, portlandite, monocarbonate and SiO2. Thermodynamic modeling was further used to predict possible changes in the hydrate assemblage and the pore solution as hydration progresses.