- Definition of manufactured sand
According to the national standard, all machine-made sand and mixed sand treated by soil removal are collectively referred to as artificial sand. The specific definition of machine-made sand is the rock particles with particle size less than 4.75mm produced by mechanical crushing and screening, but does not include the particles of soft rock and weathered rock.
- Specification of manufactured sand
At present, the artificial sand is basically medium coarse sand with fineness modulus between 2.6-3.6. The particle grading is stable and adjustable and contains a certain amount of stone powder. Except that the 150m sieve residue is increased, the rest sieve residue is mostly triangular or rectangular, with rough surface and sharp edges and corners. However, due to the different production ore sources of manufactured sand and the different equipment and processes for producing and processing manufactured sand throughout the country, the particle type and gradation of manufactured sand may be very different. For example, some manufactured sand has more flake particles, and some manufactured sand has a large particle gradation at both ends and small in the middle, but as long as it can meet all the technical indexes of artificial sand in the national standard, It can be used in concrete and mortar. Those that fail to meet the technical requirements of national standard artificial sand cannot be used, because the particle shape and gradation of manufactured sand can be adjusted and improved. At this point, artificial sand is essentially different from natural sand. The above characteristics are reduced by the mixing proportion of mixed sand.
The specifications of manufactured sand are divided into coarse, medium, fine and ultra-fine according to fineness modulus (MX):
The fineness modulus of coarse sand is 3.7-3.1, and the average particle size is more than 0.5mm;
The fineness modulus of medium sand is 3.0-2.3, and the average particle size is 0.5mm-0.35mm,
The fineness modulus of fine sand is 2.2-1.6, and the average particle size is 0.35mm-0.25mm;
The fineness modulus of ultra-fine sand is 1.5-0.7, and the average particle size is less than 0.25mm;
The larger the fineness modulus, the coarser the sand. The smaller the fineness modulus, the finer the sand.
- Grade and use of manufactured sand
(1) Grade: the grade of manufactured sand is divided into three grades: I, II and III according to its skill needs.
Class I sand is applicable to concrete with strength grade greater than C60;
Class II sand is applicable to concrete with strength grade c30-c60 and frost resistance, impermeability or other requirements;
Class III sand is applicable to concrete and construction mortar with strength grade less than C30;
- Requirements for manufactured sand
The particle size of manufactured sand is between 4.75-0.15mm, and there is a certain proportion limit for stone powder less than 0.075mm. The particle size is divided into 4.75, 2.36, 1.18, 0.60, 0.30 and 0.15. The particle size shall be better and continuous, and each particle size shall have a certain proportion. The particle shape shall be cubic as much as possible, and there are certain restrictions on the content of needle and flake.
- Grain gradation of manufactured sand
The particle gradation of sand refers to the matching proportion of sand size particles. If the sand is of the same thickness, the gap between them is larger. When the two sizes of sand are combined, the gap between them is reduced. With the combination of sand with three particle sizes, the gap is smaller. It can be seen that the porosity of sand depends on the matching degree of particle size at all levels of sand. Well graded sand can not only save cement, but also improve the compactness and strength of concrete and mortar.
- Raw materials of machine-made sand
Granite, basalt, river pebble, cobble, andesite, rhyolite, diabase, diorite, sandstone, limestone and other varieties are usually used as sand making raw materials for machine-made sand. The manufactured sand is distinguished by rock types, with differences in strength and use.
- Requirements for grain size of manufactured sand
The mine configuration requires fine particles of crushed materials. Generally speaking, needle and flake materials are easier to be ground when they enter the mill. The requirements of building gravel are just the opposite, and there are strict proportion restrictions on needle and flake. The main reason is that the cube particles have edges and corners, which can lock each other between particles. At the same time, cube particles have stronger adhesion and larger surface area than needle flake particles and circular particles.
- Characteristics of manufactured sand
The characteristics of concrete prepared with artificial sand are: the slump is reduced and the 28d standard strength of concrete is improved. If the slump remains unchanged, the water demand increases. However, after the water cement ratio increases without adding cement, the measured strength of concrete does not decrease under normal circumstances. The concrete proportioning design according to the law of natural sand shows that the water demand of artificial sand is large, the workability is slightly poor, and it is easy to produce bleeding, especially in low-strength concrete with less cement; If the concrete proportion design is carried out according to the characteristics of artificial sand, the concrete with good workability can be prepared by reasonably using the stone powder in artificial sand and adjusting the sand rate of artificial sand. The proportioning design method in the code for proportioning design of ordinary concrete is completely suitable for artificial sand. The fineness modulus of artificial sand most suitable for concrete preparation is 2.6-3.0 and the grading is zone 2.
- Inspection standard for manufactured sand
The state has standardized fine aggregate inspection standards, and the main inspection items include: apparent relative density, soundness, mud content, sand equivalent, methylene blue value, angularity, etc.