1. Standard for Quality and Inspection Methods of Sand and Stone for Ordinary Concrete stipulates: silt content of sand: concrete strength grade is greater than or equal to C60, and silt content is less than or equal to 2.0%; C55-C35 is not more than 3.0%; When the strength grade is less than C30, the silt content is not more than 5.0%. Mud content of coarse aggregate (gravel or pebble): greater than C60 and less than 0.5%; C55-C35 is not more than1.0%; When the strength grade is less than C30, the silt content is not more than 2.0%. 2. High silt content not only affects the strength of concrete, but also has a great influence on the durability of concrete. The frost resistance is obviously reduced, because the mud content in concrete will affect the uniformity of concrete: the bond between cement stone and gravel and cement stone; Unsealed air space will be formed in concrete; Moreover, in the case of freezing and thawing, the expansion rate and shrinkage rate of mud are different from those of concrete, so the durability of concrete is greatly affected. 3. The excessive mud content in sand and gravel reduces the bond strength of concrete aggregate interface and the tensile strength of concrete, which is not conducive to controlling concrete cracks. 4. It reduces the grip of cement slurry on coarse aggregate, thus reducing the strength of concrete. 5. Excessive mud content will reduce the internal friction between cement and macadam, increase internal stress, cause sliding and eventually crack, and reduce strength. In addition, too much mud may corrode steel bars and reduce their strength.