The Use of Classified Fly Ash to Produce High Performance Concrete

Waste materials may be upgraded to specification standards and occasionally to premium materials for use in the preparation of composites or for use on their own. The treatment for upgrading is a matter of cost and of the potential environmental problems that the treatment can create. The investigation presented in this paper shows an example of the improvements of fly ash properties achieved by a simple physical process, that is, air cyclone separation. This process gives a very fine ash with adequate pozzolanic activity and is suitable for producing high performance concrete with excellent durability, particularly when exposed to aggressive environments. This paper presents data on the properties of the fine fly ash, including lime reactivity, composition, size distribution and shape. The investigation was carried out using two fly ashes obtained by the process of air separation, using a prototype small air cyclone separator and an air mini-splitter. The properties of these ashes were compared to the properties of the original raw ash and with the properties of a fly ash processed industrially by the conventional mechanical separation process, which produces a fly ash conforming to the appropriate British specifications for use in the production of structural concrete. In this test programme, high performance concrete made with 0.3 fly ash and 0.7 ordinary Portland cement (by weight) as binder was assessed by measuring strength, porosity, and permeability. These properties were used to evaluate the performance of concrete and potential long term durability.