Development of novel processing for the production of low-cost by-product fillers as a replacement for high-cost primary fillers- REFILL
The objective was to develop saleable 'by-product' fillers (BPFs) from the mineral residues of aggregate quarries. Two quarries were studied, namely siliceous residues from a quarry in Ireland and calcareous residues from a quarry in Greece. A study was also made of an innovative grinding technique, the Vortex Grinder, for particle size reduction to optimise the uses and value of the residues. The end users had interests in using the BPFs for elastomeric membranes, paints, GRP, paper, asphalt, concrete, sub-base and artificial soil. The Vortex Grinder has been able to produce fine powder from large particle feedstock and to lower the mean particle size of fine powders. The siliceous and calcareous BPFs have been shown to be suitable for use in elastomeric membranes and a large-scale trial has been carried out on the calcareous material. Several paints were formulated with calcareous BPFs but the results were disappointing. However, it was possible to formulate paints of reasonable quality by partially substituting extenders with Micronised BPFs. The use of calcareous MBPFs in the production of GRP panels was also studied and it has been shown that a partial replacement of extenders does not impair the quality of the panels produced. It has been concluded that the calcareous MBPFs may be incorporated in paper pulp by up to 5% as a substitute for expensive wood pulp, without any major changes in the production procedure. For the siliceous material, altering the ratio of the 0-2mm and blending it with washed 3mm gives acceptable retained stiffness and results in a fine aggregate source for use in a range of asphalt products. Work on siliceous BPFs for concrete has not been conclusive and further work is required. Practices have now been adopted which enable the sub-base to meet the Type-1 specification. The most economical option is to blend in a 0-1mm fraction, which has been washed out of the 0-2mm. When required this is now the preferred practice adopted by the quarry. Large-scale trials on artificial soils manufactured from composts and siliceous BPFs appear to be performing well for tree growth but are slightly under par as a growing media for grass.