Sand is one of main materials of concrete and mortar, and it's also a material in civil engineering. Generally, sands are classified into natural and man-made sand. Formed by the natural conditions (mainly the weathering of rocks), the size below 5mm is called natural sand. Man-made sand is made by machine, that is cleaning the soil crushed by the machine, after screen the size is belown 4.75mm.But don't contain the particles of soft and weathered rocks. According to the specification of sand fineness modulus(the index of characterization of natural sand particle size and thickness of coarse as below:),sands fineness is classified into large, middle and small.

The Fineness modulus is more larger, it's means the size of sand is more larger. The fineness modulus of the comer concrete sand  is between 3.7 to 1.6,or use the large,adding a little small sand,the ratio:4:1.

The mixture of sand particle is the mixing proportion of the sand particles. If it's the same size of sands, the interspace is largest, the two kinds size of sand mix, the interspace will decrease, the three kinds size of sand mix, the interspace is smaller. Thus, the porosity of the sand depends on the mixing of sand at all levels. Good level of sand, still can not only save the concrete and improve the mortar's density and intensity.