Erkundung und Modellierung der Verformungsmechanismen von Zementstein auf der Grundlage neuartiger Röntgen-Kleinwinkelstreuuntersuchungen
Zusammenfassung der Projektergebnisse
The processes involved in deformation of hardended cement paste (hcp) in its highly porous gel structure are not well understood. The objective of the present project was therefore to explore the microstructural mechanisms of creep in hcp by means of experimental investigations and, above all, to narrow down the structural size at which creep processes take place. For this purpose, creep and shrinkage tests were carried out on small-format hcp samples, whereby, in addition to the deformations, the structural changes occurring in the hcp were observed in-situ using small- and wide-angle X-ray scattering experiments (SAXS and WAXS methods). In a first step, a test rig was developed to enable combined creep and SAXS investigations. In a next step, very extensive combined tests were then carried out on hcp samples with different w/c ratios and moisture contents. The investigations showed that the theory of Feldmann and Sereda, according to which creep is due to sliding processes within individual C-S-H particles on a scale of < 5 nm, does not appear to be tenable. Instead, it was clearly shown that creep leads to significant changes in the structure size range between approx. 5 nm and 20 nm, which confirms Powers' theory. A quantification of the processes using the Porod theory as originally intended, proved to be unsuccessful, so that a method based on mass fractality had to be developed. The understanding of the microstructural processes and, above all, the influence of moisture content, developed in this way, now enables the further development of macroscopic creep models, but this was not the subject of the present project.
