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