Sand is an integral part of concrete. It is generally called fine aggregate, which refers to rock particles with a particle size of less than 5mm. It can be generally divided into natural sand and artificial sand.

At present, common sands are:

(1) Manufactured sand; (2) River sand (generally used for sand designated for key projects, and ordinary concrete is generally not used due to high price and small quantity); (3) Stone chip powder (produced as a by-product of crushed stone, with more particles at both ends and less in the middle, broken grading, more flake particles and more powder); (4) River sand (super fine sand, fineness modulus below 1.6, minimum 0.5); (5) Washed sand (including mountain sand, ancient river terrace sand, etc.); (6) Sea sand (most of them have not been desalinated, and some people secretly sell them after mixing 20% ~ 50% of the river sand); (7) Weathered sand (including weathered mountain sand and sand made of clay rock, argillaceous shale, argillaceous sandstone, marl, argillaceous slate and completely weathered rocks. The sand made of this rock has low strength, poor firmness, many soft particles, can not play a skeleton role in concrete, and has large water demand and adsorption); (8) Mud and sand (including unclean desilting sand, etc., with a maximum mud content of more than 20%); (9) Steel slag sand (poor stability); (10) Solid waste processing sand [including construction waste, sand making from waste lime yard materials (including discarded overburned and unburned lime blocks, etc.)], etc.

What is the difference between river sand, machine-made sand, washed sand, recycled aggregate, tailings sand and other sand used for concrete? What are the advantages and disadvantages?

River sand

River sand is a non-metallic ore produced by repeated collision and friction of natural stones under natural conditions through the force of water for a long time. Its composition is relatively complex, the surface has a certain smoothness and contains a lot of impurities. River sand particles are smooth, relatively clean and come from a wide range of sources. Application: river sand is cement standard sand, which is mostly used in construction, concrete, cementitious materials, road building materials, artificial marble, cement physical property inspection materials (i.e. cement standard sand), etc. The prepared concrete mixture has rich, full and dense slurry and good fluidity.

Machine-made sand

The mechanical particle size of the crushed sand is less than 754.4 mm. The finished product is more regular and can be processed into sand of different rules and sizes according to different process requirements. The slurry has the strongest binding force in concrete and can better meet daily needs.

Washing sand with water

Washing sand: refers to the sand in the river or on the old river bed. Through washing and classification, various grades and specifications of sand are separated. Because the washed sand is dug directly from the river, it will be mixed with small pebbles and fine sand. These pebbles are washed by the river for a long time, and their edges and corners are relatively round.

Recycled aggregate (construction waste)

The recycled aggregate of simple broken construction waste has many edges and corners, rough surface, and the components also contain hardened cement mortar. In addition, a large number of micro cracks are caused inside the concrete block due to damage accumulation in the crushing process, resulting in large porosity, large water absorption, large stacking porosity, high crushing index value and small stacking density of the recycled aggregate of construction waste, which can not be used on a large scale.

Sea sand

After desalination, the sea sand with chloride ion content less than 0.02% can be used in engineering.

Sand making from waste residue and tailings

At present, steel slag sand and quicklime granular sand are used in the market. The disadvantages of these two kinds of sand are poor volume stability or high content of heavy metal ions, high post-treatment cost and high quality risk.