Combined Use of Fly Ash and Blast Furnace Slag as Concrete Additions

Project Number 309

The use of fly ash as pozzolanic concrete addition has been practiced in Germany for more than thirty years and it is laid down in the technical regulations. Ground granulated blast furnace slag has so far only been used as main constituent for the cement production. With the new European Standard for ground granulated blast furnace slag as latent hydraulic concrete addition (EN 15167), the use of ground granulated blast furnace slag as concrete addition will be possible in the future.

The tests shall verify that the properties of concretes made of Portland cements (CEM I) with the additions ground granulated blast furnace slag and fly ash are comparable to those of concretes made of blast furnace slag cement (CEM II/B-S, CEM III/A and CEM III/B) with fly ash. The investigations shall be conducted with cements of different kinds and strength classes as well as with fly ash and ground granulated blast furnace slag of different fineness. The grain size distributions of the single concrete raw materials are of special importance. The optimization of the binder properties will be made on mortars. Especially workability, air content and bulk density will be determined on the fresh mortar. On the hardened mortar, flexural tensile strength, compressive strength as well as carbonation behaviour will be determined. These properties will be verified on concretes samples.

Starting in January 2008 and finishing in September 2010, the project is carried out by the Institute of Building Materials Research (ibac) of RWTH Aachen University directed by Prof. Brameshuber and is technically supervised by the Working Panel Power Plant By-products . It is supported by the Federal Office for Building and Regional Planning within the framework of the research initiative "Future Building".