buy mm crushed rock. 25mm Crushed Gravel BURNCO Landscape Supplies. 25mm Crushed Gravel is a mixture of sand, rock fines and rock that is best used as a packing gravel for underneath asphalt, concrete, driveways, garage pads, retaining walls and paving stones. It is a compaction material also known as 3/4" crush and road crush. 40mm Crushed Rock BURNCO Landscape Supplies. 40mm Crushed Rock .