Fly Ash Aggregates


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Title: Fly Ash Aggregates

Author(s): J. Bijen

Publication: Special Publication

Volume: 79


Appears on pages(s): 495-518

Keywords: aggregates; bonding; briquetting; costs; energy; fly ash; manufacturing; pelleting; sintering.

Date: 5/1/1983

The disposal of powdered coal fly ash is meeting objections, especially in heavily populated areas. The rate of utilization, however, in any country rarely exceeds fifty percent. In the Netherlands attention has been drawn to the production of artificial aggregates from fly ash to obviate the need of disposal. This is stimulated by the increasing scarcity of exploitable resources of coarse aggregates. This paper discusses a number of techniques to produce artificial aggregates from fly ash and describes methods of agglomerating and bonding of fly ash particles. The main agglomeration techniques are agitation and compaction. Bonding processes are subdivided into sintering, hydro-thermal processes and 'cold' bonding. In cold bonding the pozzolanic behaviour of fly ash is used. As a binder, lime or cement is applied, and optionally additions of calcium sulfate or sulfite. For each type of bonding one aggregate is evaluated. The fly ash aggregate processed on a sintering grate showsthe best quality and also has the lightest weight. The costs Of production are lowest for the cold bonded product, which seems to be competitive with ordinary natural aggregate in the Netherlands. However, to obtain the same target strength more Cement will be needed for the artificial fly ash aggregates.