Changes in volume (quantity) by mixing components : trials on a small-scale and on a full-scale (factory)

Addition of minerals to organic components often cause changes in the final volume of a growing medium (increases or more frequently decreases), especially in case of mixing components with particles of different sizes and bulk densities. An experimental study was conducted, comprised of a small-scale trial in laboratory and a full-scale trial in five growing media companies. In the lab trial two mixtures (peat/pumice and peat/compost in different ratios) were prepared in a concrete mixer, and measured and theoretical volumes (EN 12580) were compared. In the full-scale, changes in volumes of an expected 80:20 vol:vol mixture of peat and pumice were studied after blending and packaging. In the lab, trial mixture volumes decreased linearly with increasing doses of pumice (up to 15% of reduction); on the contrary compost had a minimal effect on the final volumes. Reductions in volume were observed also in the full-scale trial, especially after packaging and the extent could be related with the highest dosages of pumice and with the addition of water during processing. During bags storage on pallets further drops of volume were noticed. The small-scale procedure can be predictive of the reduction of volume of the binary mixtures tested in plants.