Sand aggregate is a general term for materials such as sand, pebble (gravel) gravel, crushed stone, block stone, aggregate stone, etc. Sand and gravel aggregates are the main building materials for concrete and piled stones in water conservancy projects. Humans use it to build and transform the world, consuming tens of billions of tons of gravel aggregates every year. Aggregate accounts for 60% to 75% of the volume of hardened concrete and is the main component of concrete.
1. Classification of sand and gravel
Sand is one of the main components of concrete and mortar, and it is a bulk material for civil engineering. Sand is generally divided into natural sand and artificial sand.
Natural sand: Rock particles formed by the action of natural conditions (mainly rock weathering) and having a particle size below Smm.
Artificial sand is machine-made sand: it refers to rock particles with a particle size of less than 4.75mm made by mechanical crushing and sieving after earth removal treatment. However, it does not contain soft rock and weathered rock particles.
Construction sand is generally divided into fine sand, medium sand, medium coarse sand and coarse sand. Medium coarse sand for general concrete and mortar. The specifications of sand are divided into three types: coarse, medium and fine according to fineness modulus (an indicator of the degree and type of natural sand particle size). Coarse sand: The fineness modulus is 3.7 ~ 3.1, and the average particle size is more than 0.5mm. Medium sand: Fineness modulus is 3.0 ~ 2.3, average particle size is 0.5 ~ 0.35mm. Fine sand: The fineness template is 2.2 ~ 1.6, and the average particle size is 0.35 ~ 0.25mm. Extra fine sand: The fineness modulus is 1.5 ~ 0.7, and the average particle size is 0.25 mm or less. The larger the fineness modulus, the coarser the sand.
The fineness modulus of ordinary concrete sand ranges from 3.7 to 1.6, that is, between the modulus coefficients of fine sand and coarse sand, especially medium sand, or coarse sand plus a small amount of fine sand, the ratio is 4: 1. The particle gradation of sand refers to the mixing ratio of sand-sized particles. If it is the same thickness of sand, the gap is the largest. When the two sizes of sand are combined, the gap is reduced. When the three sizes of sand are matched, the gap is smaller.
It can be seen that the porosity of the sand depends on the matching degree of the particle size of the sand. The graded sand not only saves cement, but also improves the density and strength of concrete and mortar.
Construction gravel is generally divided by particle size, such as melon seeds (0.5 ~ 1 cm), two or four ballast (2 ~ 4 cm), etc., and by material, such as concrete, there are often two types, one It is pebbles and one is gravel.
Stone refers to particles with a particle size greater than 4.75 mm. There are two kinds of gravel and pebble. Crushed stone is a particle with a particle size greater than 4.75 mm made by natural rock or rock rupture and sieving; pebble is a particle with a particle size greater than 4.75 mm formed by natural weathering, water flow handling and sorting.
The length of the particles in the pebbles and crushed stones is greater than the corresponding particle size of 2.4 times the average particle size of the particles are needle-shaped particles, the thickness is less than 0.4 times the uniform particle size is flaky particles. Uniform particle size refers to the uniform value of the upper and lower limits of the particle size.
Natural gravel refers to the loose confusion of sand and gravel, consisting of rock debris and cement. The composition of the rock is mainly quartz and feldspar, which is related to the surrounding area of the production area or the type of rock exposed in the upper reaches of the channel; the cement in the rock is commonly calcareous, siliceous, iron, and muddy. Difference.
Differences The layout of sand and gravel is quite different, some particles have uniform thickness and some are different in size; some sand and gravel have good roundness and some sand and gravel have sharp edges and corners. Sand and gravel are loose objects, but their granules are usually harder and their chemical properties are stable.
Natural sand and gravel are usually obtained by sieving directly from natural sand and gravel resources. The machine-made sandstone is obtained by mining the mountain and processing the ore through cracking, sieving and shaping. Mechanism sandstone follows the characterization of natural sandstone.
In practical use, the fineness modulus of sand and gravel can only be used as a reference, and we must pay attention to the true gradation of sand and gravel.
2, the source of sand
People usually call the sand collected from rivers, mountains, seas, etc. river sand, mountain sand, and sea sand, or collectively called natural sand, which is a natural mineral resource. With the increase in construction, deployment of gates, bridges, and foundation equipment, as well as the elimination of natural sand and gravel resources and the limited exploitation of shelter conditions, mining mines have been used as an important source of machined gravel over the past year.
The minerals commonly used in machine-made sandstone include: magmatic rocks, sedimentary rocks, and metamorphic rocks. Magmatic rocks are divided into: basalt, andesite, gritstone, rhyolite, granite, syenite, diorite, gabbro, peridotite; sedimentary rocks are divided into: conglomerate, sandstone, siltstone, limestone, dolomite ; Metamorphic rocks are divided into: marble, quartzite, gneiss, corner shale, serpentine. Poor other mines have different physical and chemical properties.
3. The role of sand and gravel in construction and foundation methods
Sand and gravel is the base material in the deployment of national economic settings and equipment. It is used for foundation engineering, concrete, mortar and corresponding finished products. Wait for the basic method to set up the indispensable aggregate materials for equipment deployment. Currently, cement concrete is the largest and most widely used in engineering equipment deployment, followed by asphalt concrete, and the amount of polymer concrete is relatively small.
Concrete is a kind of composite material, and sand and gravel is one of the most important component materials among them. In the concrete layout, sand and gravel play an important role as a skeleton, stabilizing the volume of concrete, reporting stress, and restraining shrinkage to prevent cracking. It plays an extremely important role in construction and foundation methods. It can be said that without sand and gravel, there would be no concrete, and there would be no concrete construction and foundation engineering.
The sandstone people are familiar with and understand the sandstone production, transportation, application and equipment related knowledge, which is crucial to the future direction of the sandstone industry, so as to be more professional in the supply of sandstone industry.