Coarse sand:Its fineness modulus is 3.1-3.7, and the average particle size is 0.5mm or more; Medium sand:Its fineness modulus is 2.3-3.0, and the average particle size is 0.35-0.5mm; Fine sand:Its fineness modulus is 1.6-2.2, and the average particle size is 0.25-0.35mm; Super-fine sand:Its fineness modulus is 0.7-1.5, and the average particle size is 0.25mm or less.