Handling alternative fuels - A progress report

The initial position for the research project was the increase in general technical approvals for cements that according to DIN 1045-2 are not approved in principle in Germany for all exposure classes. Various durability tests that are described in, for example [1], have to be carried out as part of the approval procedure. However, the corresponding test procedures are time-consuming and cost intensive. In a joint research project VDZ gGmbH and Clausthal Technical University have therefore identified some characteristic values based on degree of hydration that allow conclusions to be drawn about durability criteria. This could support and possibly accelerate the procedure for assessing cements that require general technical approval. Before the actual durability testing, which is not to be replaced but only amplified by the results of this research project, it is possible to test whether a cement is suitable to pass such a test. The concrete mix formulations are precisely defined in the approval test plans so the characteristic values developed in this research project are not aimed at concretes with arbitrary compositions but at cements with arbitrary compositions in defined concrete mix formulations. It has been possible to show that in most cases the concrete or mortar compressive strengths of the cements investigated in this research project provided only weak guide values or none at all for the results of the durability investigations. On the basis of the degree of hydration of the hardened cement paste and the porosity of standard mortars it was possible to identify characteristic values that seem suitable for carrying out an assessment with respect to the particular acceptance criteria of the durability tests. No tests on hardened concrete are needed for determining the characteristic values. The durability of concretes with compositions that conform to the approval test plans can be estimated with the aid of the properties of the hardened cement paste and mortar.