SEM-investigations on the microstructure of steam cured building materials: Fid-Bau Portal

SEM-investigations on the microstructure of steam cured building materials

Walk-Lauffer, B. / Huber, M. / Hums, D. / Knöfel, D. / Zürn, S.G.

Quartz sand, water, lime (and cement) are the raw materials of steam cured building materials. This kind of materials has been proved in the past in many fields of application. Most of their binding phases belong to the system CaO-SiO2-H2O (CSH). In autoclaved aerated concrete (AAC) crystallised CSH-phases (C-S-H I, 1.13 nm tobermorite) form about 50-80 wt.% of total solids during the hydrothermal process. To improve the technical properties of the hardened material it is of interest to know the kinetics of the phase evolution during the hydrothermal treatment and how the reactions are influenced by foreign cations. On that background the experimental scope is twofold: Influence of the foreign cations AL(3+) and K(+) on the basic system CaO-SiO2-H2O. Application to industrially relevant systems. The kind and morphology of the CSH phases depend strongly on the temperature and the chemical composition of the starting materials. This is valid for the model systems as well as for industrial products. Aluminum stabilizes 1.13 nm tobermorite and hinders the transformation to xonotlite. Alkalis disturb the crystallization and lead - in high concentrations - to near amorphous CSH phases in the product. The crystallinity of the CSH phases correlate with the distribution of the size of the air pores. The observed change in the microstructure affects the macroscopic properties. With increasing crystallinity of 1.13 nm tobermorite in the material - in well defined ranges - an improvement of the physico-mechanical properties of the products can be expected.