Evaluation of the risk potential of concrete compositions

Economic reasons sometimes rule out the replacement of locally available, alkali-sensitive aggregates. In these cases, it is necessary to design concrete compositions that comprise the cements and additions available locally on the one hand and are not vulnerable to harmful ASR on the other hand. In order to be able to reliably assess these concrete mix formulations, a method allowing to test realistic concrete compositions for a potential harmful ASR in as little time as possible has to be developed. Such a performance test method is currently being developed as part of a research project sponsored by the AiF.

Fig. 1: Cabinet for storing bars at 60 °C over water Fig. 2: Expansion of concrete prisms (10 x 10 x 50 cm) with silica fume subjected to different types of storage

Work proceeds on the basis of a concrete test method developed in France, which consists of storing concrete prisms at 60 °C over water (Fig. 1) and measuring their length change as a function of time. The investigations are initially aimed at comparing the behaviour of concretes during this test to that shown by concretes of the same composition stored under practical conditions. This serves to ensure that the discrepancies occurring during the storage of concrete specimens containing pozzolana in a 40 °C fog chamber (Fig. 2) are excluded in the performance test method. The specimens exposed to accelerating reaction conditions did not exhibit any expansion, while sizeable expansion and cracking were observed after storage under realistic conditions.