Determination of characteristic values based on the degree of hydration for predicting the durability of concrete

With correct composition, production and curing the essential feature of concrete as a construction material apart from its strength is its durability, i.e. its resistance to external influences. These influences can involve carbonation, frost or penetration by chlorides and can result in damage either to the reinforcement or to the concrete itself.

When using cements such as CEM II/B-M, for which there is no extensive experience with respect to durability, it is necessary to check beforehand whether they satisfy the requirements. A general building inspectorate approval (AZ application approval) issued by the DIBt (German Institute for Building Technology) is required for this purpose.

The definition of characteristic values that are simple to determine and allow conclusions to be drawn about the durability criteria would accelerate the procedure for assessing the cements. Before the actual durability testing, which was not to be replaced but only supplemented in this research project, it would be possible to establish whether a cement appears suitable for passing such a test.

Cements with several main constituents (clinker, granulated blastfurnace slag, fly ash and limestone) were produced in the research project. The individual constituents were grounded separately to different finenesses, characterised by various methods (chemical and mineralogical analysis, particle size distribution, BET) and then mixed to make CEM II/B cements and also cements that do not lie in the standard composition range for DIN EN 197-1. Mortar and concrete trials were used to determine characteristic parameters, such as the void filling of the cements, their hydration characteristics, the porosity of the mortars and concretes made with these cements, and the durability of the concretes. Characteristic values for predicting the durability were defined from the parameters relevant for each type of exposure.