Band 4, Heft 3

With the help of X-ray for visualisation of salt transport in porous building materials it is now for the first time possible to check both, the description of salt transport processes as well as the mathematical transport models used. The tests were carried out with sandstone, however the results are transferable to other building materials having a comparable pore system.

Modern methods of instrumental analysis provide very convenient ways to characterize building materials. At present, wet chemical procedures are still in use not only for sample preparation but also for the real investigation. Raster electron microsopy and x-ray diffraction are the preferred instrumental methods of analysis in many places. In this review the high potential of optical molecular spectroscopy for characterization of building materials will be demonstrated by typical examples. Extensive series of wet chemical analysis may be substituted even by a single IR spectroscopic measurement combined with modern procedures of chemometric data evaluation.

Precambrian greywacke used as concrete aggregate can lead to damage of concrete structures under certain conditions (high humidity, certain concrete composition, high alkali content). The chemical analysis of the soluble constituents of a concrete damaged in such a way always shows that the composition of the hardened cementious material of the concrete is unusual. It is possible to determine the part of the oxydic constituents which are soluble from the greywacke in the concrete by using of a specific analytical method. This method is based on two analytical steps e. g. the first step is the total analysis of the concrete and the second step is the analysis of the concrete after sorting out the greywacke grains. By this the material which is available for mineral forming reactions can be determined. The investigations of the soluble constituents determined by this method show that opal containing sandstone releases SiO 2 (silica) only, greywacke aggregates release SiO 2 too but also Al 2 O 3 , Fe 2 O 3 , MgO and K 2 O in larger amounts. The accuracy of this method is demonstrated by analysing a normal concrete containing gravel aggregates.

The heat insulation layer in old single-leaf roofs often is humid because of the roof This increased humidity is to be considered in the context of restoration measures of the roof and if the yearly moisture fluctuation has to be estimated. Knowledge based on practical experience over decades confirms that effective drying can be achieved by appropriate restoration. Quantitative prediction of the time-dependence of the drying process, however, is not possible up to now. For this reason, the success of restoration of humid old roof systems remains uncertain. In this contribution, test results and a method to calculate moisture processes will be presented. In order to describe the drying process an approach based on diffusion is supplemented by specific border conditions of roofs. Statistical climatic data and temperature as well as vapour pressure, both depending on the chosen structure, range among these parameters. By means of this calculation method, time-dependent drying can be checked and a successful restoration procedure can be suggested. Most important values entering the planning of a restoration measure will be discussed.

Damage at renderings in base zones caused by splash water are often observed. During this procedure, different situations have been investigated. Several types of renderings and paint systems as well as the exposition of the buildings are taken into consideration. Suggestions for higher durability of renderings in the base zone are made.