Sand is a component of concrete and is generally called fine aggregate. It refers to rock particles with a particle size of less than 5mm. Generally, it can be divided into natural sand and artificial sand.
Common sands are:
(1) Machine-made sand;
(2) River sand (usually used for designated sand for key projects, and ordinary concrete is generally not used because of the high price and low quantity); (3) Stone chip powder (the by-product of the production of crushed stone, the particle distribution is more than at two ends and less in the middle, with broken grades. More flake particles and more powder);
(4) Jiang sand (extra-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, some people mix 20%-50% in river sand and sell them secretly);
(7) Weathered sand (including weathered mountain sand and sand made of claystone, argillaceous shale, argillaceous sandstone, marl, argillaceous slate and all kinds of fully weathered rocks, etc., sand made from this kind of rock Low strength, poor firmness, many weak particles, can not play a skeleton role in concrete at all, and require large water and high adsorption);
(8) Mud sand (including dredged sand that is not cleaned, etc., the highest mud content is more than 20%);
(9) Steel slag sand (with poor stability);
(10) Solid waste processing sand [including construction waste, waste lime yard waste (including discarded over-burned and under-burned lime blocks, etc.) sand making], etc.
River sand
River sand is a non-metallic ore that is produced by repeated collisions and frictions of natural stone under the force of water for a long time in its natural state. Its composition is more complex, the surface has a certain degree of smoothness, and the content of impurities is high. River sand particles are smooth, relatively clean, and have a wide range of sources.
Uses: River sand is cement standard sand, which is mostly used in construction, concrete, cementitious materials, road materials, artificial marble, cement physical performance inspection materials (ie cement standard sand), etc. The configured concrete mixture slurry is rich, full and dense, with good fluidity.
Machine-made sand
The machine-made sand refers to the rock particles whose particle size is less than 4.75mm after being broken by machinery. The finished product is more regular and can be processed into sand of different rules and sizes according to different technological requirements. The paste has the strongest binding force in concrete and can better meet daily needs.
Washed sand
Washed sand: refers to the sand in the river or the sand on the old river bed through washing and sorting to separate sand of various grades and specifications. Because the washed sand is dug directly from the river, it will be mixed with small pebbles and fine sand. These small pebbles are washed by the river for a long time, and the edges and corners are relatively round.
(Construction waste) recycled aggregate
Simple crushing of construction waste recycled aggregate has many edges and corners, rough surface, and hardened cement mortar in its components. In addition, the damage accumulated in the concrete block during the crushing process causes a large number of micro-cracks inside, resulting in the pores of the construction waste recycled aggregate itself It can not be used on a large scale because of its high rate, high water absorption rate, high bulk porosity, high crushing index value and low bulk density.
Sea sand
After desalination treatment, sea sand with a chloride ion content of not more than 0.02% can be used in engineering.
Sand making from waste residue and tailings
At present, there are steel slag sand and quicklime granular sand in the market. The disadvantages of these two kinds of sand are poor volume stability or high heavy metal ion content, high post-processing cost and high quality risk.
