Performance of BFS concrete: k-Value concept versus equivalent performance concept

Focusing on sustainability, the use of industrial by-products as cement replacing materials has become a common tendency and we are still trying to increase the replacement level without negatively affecting and even with the aim to improve some of the concrete’s properties (e.g. compressive strength, workability and durability). However, following the descriptions of the k-value concept of EN 206-1 (2000) and NBN B15-001 (2004) for type II additions, the use of high contents fly-ash (FA) or blast-furnace slag (BFS) is not allowed in more demanding environments and these concrete types can only be applied when the equivalent performance with a proper reference is proven (EN 206-1 (2000) and NBN B15-100 (2008)). Moreover, while the k-value concept is a generally known principle to determine the influence of these additions on strength, k-values are not commonly used for durability indicators. In this study, the two concepts (k-value concept and equivalent performance concept) are critically evaluated for BFS concrete. accelerated degradation tests were performed to investigate the resistance of Ordinary Portland cement (OPC) and BFS concrete against organic acids, carbonation, chloride ingress, sulphate attack (complete submersion) and the alkali–silica reaction. The cement replacement percentages varied from 50% to 85% and the influence of different curing periods was considered. The results showed that the performance of BFS concrete was better than that of OPC concrete, except for carbonation. Afterwards, the results were evaluated with the k-value concept and the equivalent performance concept. The latter method seemed to be the most promising one and application of the k-value concept, with respect to durability, seems to be ambiguous and laborious.