PEBBLES, GRAVEL, BROKEN OR CRUSHED STONE, OF A KIND COMMONLY USED FOR CONCRETE AGGREGATES, FOR ROAD METALLING OR FOR RAILWAY OR OTHER BALLAST, SHINGLE AND FLINT, WHETHER OR NOT HEAT-TREATED, MACADAM OF SLAG, DROSS OR SIMILAR INDUSTRIAL WASTE, WHETHER OR NOT INCORPORATING THE MATERIALS CITED IN THE FIRST PART OF THE HEADING, TARRED MACADAM, GRANULES, CHIPPINGS AND POWDER, OF STONES OF HEADING 2515 OR 2516, WHETHER OR NOT HEAT-TREATED