Common classifications of sand and gravel aggregates and what conditions should be met for good aggregate gradation?
Sand and gravel aggregate is a general term for materials such as sand, pebbles (gravel), gravel, block stones, and aggregate stones in engineering construction.(stone crusher) It is the main building material for structures such as concrete and piled stones. It plays an important role in the fields of construction, transportation, environmental protection, etc. Playing a vital role, its classification can be divided based on its aggregate particle size, aggregate density and source.
According to their sources, sand and gravel aggregates can be divided into natural rock aggregates (gravel, pebbles, sand, etc.), recycled aggregates (crushed concrete, broken bricks, etc.), artificial aggregates (manufactured sand, expanded shale, Slag, powdery slag, etc.).
According to its particle size, it can be divided into coarse aggregate (particle size greater than 4.75mm) and fine aggregate (particle size less than 4.75mm).
According to its density, it can be divided into three types: heavy aggregate (density 3500~4000kg/m³), light aggregate (density 0~1000kg/m³), and ordinary aggregate (density 2500~2700kg/m³).
Regardless of the type of sand and gravel aggregate, its gradation has a great impact on the workability and economy of concrete, and directly affects the strength, impermeability, frost resistance, corrosion resistance, and durability of concrete. The better the gradation of sand and gravel aggregates, the higher the compressive strength of concrete and the greater the bearing capacity. From an economic point of view, the probability of problems and losses will be smaller.
It is understood that a good aggregate gradation should meet the requirements of screening range, maximum particle size, minimum particle size, uniformity coefficient and deviation coefficient, impurity content and particle shape to ensure the quality of the concrete production process. and performance.
Impurity content: controlled below 5% of the total weight;
Minimum particle size: should not be less than 0.15mm;
Maximum particle size: When the concrete strength requirements are high, the maximum particle size should not exceed 25mm. In some special cases, such as dams, bridges and other projects, the maximum particle size can reach over 60mm;
Particle shape: uniformly round or nearly round, avoiding sharp edges or irregularly shaped particles;
Screening range: The aggregate gradation should meet a certain screening range, that is, there is a certain proportional relationship between different particle sizes. Normally, the aggregate should be screened through 4 different particle size screens, each of which is 5mm. , 10mm, 20mm and 40mm, among which, the particle size between 5–10mm accounts for 15–30% of the total weight; the particle size between 10–20mm accounts for 40–60% of the total weight; the particle size between 20–40mm The particle size accounts for 25–40% of the total weight; the particle size above 40mm accounts for no more than 5% of the total weight;
Uniformity coefficient and deviation coefficient: The uniformity coefficient refers to the ratio between two adjacent sieve holes in the aggregate gradation. It should generally be between 12–1.5. The deviation coefficient refers to the ratio of each sieve hole in the aggregate gradation. The degree of difference between the proportion and the standard proportion, the deviation coefficient should be less than 0.4.
We must not only judge whether the aggregate gradation is good, but also do a good job in controlling the aggregate gradation. Artificial sand and gravel aggregates are processed through vibrating feeders, crushers, sand making machines, vibrating screens, sand washing machines, etc. It is jointly produced by the equipment, so if we want to control the gradation of aggregates, we can adjust the discharge opening size of the crushing equipment and sand making equipment, combined with the screening function of the vibrating screen, and achieve gradation control through coordination between the two.
In addition, different types of sand and gravel aggregates should be configured differently in production lines. A reasonable sand and gravel production line should be selected based on factors such as the properties, hardness, and particle size of the sand and gravel aggregates. As an expert in solutions for sand and gravel aggregate crushing production lines, Xingaonai Heavy Industry can not only provide customers with crushing and screening equipment and services from a single unit to a complete system, but its professional technology covers the entire process chain of material processing. We focus on different fields Whether it is the production of sand and gravel aggregates, the utilization of construction waste resources, or the grinding and processing of metal ores, we are the first choice.
