Zum Reaktionsverhalten präkambrischer Grauwacken im alkalischen Milieu von Betonen / The reactions of precambrian greywackes in an alkaline pore solution of concretes

Two precambrian greywackes GW1A and GW1C with different structures were investigated to describe their reaction behaviour in concrete. A portlandcement CEM I, 32,5 with a high alkali content (Na₂O-eq. = 1,4 %) was used. The soluble constituents of the greywackes in the alkaline pore solution of the concrete were determined by using a special method of chemical concrete analysis. The concrete samples were storaged in a special fog chamber at 40 °C and 100 % rel. humidity until to 9 month. The following conclusions can be given:

1 The concrete samples which were made with greywacke GWIA show a damage value of about 4 to 5 by means of rifts observed. Analogeous to the damage it can be found that the concentration of the soluble constituents which were release from greywacke begins at zero and increases continual}· until the end of the investigation. A specific discussion of several soluble oxides shows enormous differences between the reactivity of certain constituents investigated.

2 The concrete samples which were manufactured with greywacke GWIC show a damage value of about 1...2 only. But the quantity of the soluble constituents which come from the greywacke is higher. Characteristically here is a shoot up of the soluble constituents after beginning of the cement hydration process. After this the content of the soluble constituents decreases again. This behaviour in chemical reactivity of greywacke investigated can be declared by different structures. The mainly differences between both the GWIA and the GWIC were the size of the greywacke constituents. The chemical reactivity which was determined immediately after the alkali attack of the pore solution of the hardened cement and the macroscopical reactivity observed by means of rifts after 9 month are not the same.