Zur Bestimmung der löslichen Bestandteile aus präkambrischen Grauwacken bei ihrer Verwendung als Zuschlag im Beton / Determination of soluble constituents from precambrian greywacke used as concrete aggregate

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 SiO₂(silica) only, greywacke aggregates release SiO₂too but also Al₂O₃, Fe₂O₃, MgO and K₂O in larger amounts. The accuracy of this method is demonstrated by analysing a normal concrete containing gravel aggregates.