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3.2 Tested materialsIn the experiments fractionated material 1 to 4 mm was used. Four combinations of materials with different densities were chosen (table 2). The combinations brick / concrete and gypsum wallboard / concrete represent typical constituents of Construction and Demolition Waste. The material combinations containing coal as light material play of coarse no part in the recycling sector. They can be considered as model mixtures of a light organic material like wood and a heavier mineral component. In table 2 the so called “separability” is given as a feature of each particular material combination. It is defined as the quotient of the two differences of solid and fluid densities: ?S -?F q = (1) ?L -?F q: Separability rS: Density of the heavier component rL: Density of the lighter component rF: Density of the fluid Table 2: Features of tested materials
The separability of a material mixture decreases with decreasing values of q. Values q > 2.5 indicate a good separability down to particle sizes of 100 µm, q > 1.25 means that a separation with minor sharpness is possible only for coarser material, mixtures with values q < 1.25 are not separable by jigging. 3.3 Evaluation of the results of the jigging processThe stratification measured visually at the end of the treatment was used for evaluation of the jigging process. A perfect stratification is achieved if no foreign particles appear in each layer over the whole cross-section. The opposite “no stratification” means both materials are mixed statistically. Table 3 shows the gradation of the visually evaluation. Table 3: Symbols used for the semi-quantitative evaluation In the case of the coal / brick and the coal / concrete mixtures the stratification was additionally measured by image analysing. The resulting numerical value indicated the portion of foreign material in the bottom layer of the heavy material.
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