Sand and gravel aggregate refers to granular materials such as sand and stone that are mixed with cement and water when making mortar or concrete. It is also called aggregate. It is a granular loose material that acts as a skeleton or filling in concrete. In concrete, sand and gravel account for about 3/4 of the total volume of concrete, which is divided into coarse aggregate and fine aggregate.

The aggregate with a particle size> 4.75 mm is called coarse aggregate, commonly known as stone. There are two commonly used gravel and pebbles. Crushed stone is made of natural rocks or rocks that are mechanically crushed and sieved, and rock particles with a particle size greater than 4.75 mm. Pebbles are rock particles larger than 4.75 mm in diameter, which are formed by natural weathering, water flow handling, sorting, and accumulation. Pebble and gravel particles whose length is greater than 2.4 times the average particle size of the corresponding particle size of the particle are needle-shaped particles; those whose thickness is less than 0.4 times the average particle size are flaky particles (the average particle size refers to the upper and lower limit of the particle size Average diameter). Pebbles and crushed stones for construction shall meet the technical requirements of the national standard GB/T 14685-2001 "Pebbles and Crushed Stones for Construction".

Aggregates with a particle size of <4.75 mm are called fine aggregates, commonly known as sand. According to the source of production, sand is divided into two types: natural sand and artificial sand. Natural sand is rock particles with a particle size of less than 4.75 mm formed by natural weathering, water transport, sorting, and accumulation, but does not include soft rock and weathered rock particles. Natural sand includes river sand, lake sand, mountain sand and desalinated sea sand. Artificial sand is a general term for machine-made sand and mixed sand that have been treated with soil removal. The more common ones are garnet sand and natural emery sand.

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