Nano-structural Changes of C-S-H in Hardened Cement Paste During Drying at 50°C

Y. Aono, F. Matsushita, S. Shibata and Y. Hama Journal of Advanced Concrete Technology, 5(3) 313-325, 2007 Pore structural changes in hardened cement pastes, subjected to drying and wetting/drying cycles, were studied at micrometer and nanometer levels. Characterization techniques included Nuclear Magnetic Resonance (NMR), nitrogen and water vapor adsorption, mercury intrusion porosimetry (MIP) and under-water weighing. Coarsening of pore structure was observed with MIP and increase in the true density of C-S-H was suggested by the result of under-water weighing. Decrease in specific surface area due to drying was observed with nitrogen adsorption, and water vapor adsorption associated with Excess Surface Work (ESW) analysis suggested a development of cohesive structure in C-S-H. NMR confirmed polymerization of silicate anion chains. The drying-induced coarsening of pore structure is probably attributed to polymerization of silicate anion chains and development of cohesive structure in C-S-H.

In this paper the nano-structure of CSH has been analysed by means of a number of different test methods. The authors obtain interesting conclusions by combining all experimental results. This contribution increases our insight into the nano-structure and the relevance for material properties. (Prof. F. H. Wittmann, Aedificat Institute Freiburg, Germany)