Use of Hard Coal Fly Ash as Concrete Addition in Self-compacting Concrete with Alkali-sensitive Aggregates

Project Number 249

Self-compacting concrete is being increasingly used in the building industry. Advantages in the building construction result from a better accuracy of concrete surfaces and from saving time-intensive compaction due to self-compacting properties of these concretes. Thus, lower noise emissions are guaranteed for the construction of buildings and precast components, which on one hand enable night works on construction sites and on the other hand clearly improve the working conditions in precast element plants. The suitability of fly ash for the production of self-compacting concrete was already proved in a former VGB research project (VGB 209). Examinations on durability properties had not been performed by now.

In the framework of this research project it is to be proved that in combination with low alkali cement a high amount of fly ash can be used as concrete addition for the production of SCC to prevent a damaging alkali-silica reaction. This has also to be proved when using Portland cements with a high alkali content (NA2O equivalent more than 1 % by mass).

The impact of fly ash on the expansion of concrete or mortar specimen is examined with an already used concrete mixture with cement with a low alkali content (NA cement) and a Portland cement with a high alkali content as well as alkali sensitive aggregates.

The impact of fly ash on a damaging alkali-silica reaction is controlled by expansion tests, ultrasonic running time, crack initiation and on a spot check basis by thin section microscopy.

In addition to the storage in the fog chamber (40 °C; 99 % relative humidity) concrete samples stored outside will be tested.

The project is assigned to the VGB research programme "Waste management of coal-fired power plants and combustion plants" (ERKOM). Starting in 2003, the project is carried out by the Institute for Building Materials and Construction at the Technical University of Munich and is technically supervised by a working group of the working panel "Power Plant By-products".