What are the types and technical properties of lightweight aggregate?

1. Types of lightweight aggregate. Any lightweight aggregate with aggregate particle size above 5mm and bulk density less than 1000kg/m3 is called light coarse aggregate. Light aggregate with particle size less than 5mm and bulk density less than 1200kg/m3 is called light fine aggregate.

According to different sources, lightweight aggregate can be divided into three categories: ① natural lightweight aggregate (such as pumice, volcanic slag and light sand); (2) Industrial waste lightweight aggregate (such as fly ash ceramsite, expansive slag, spontaneous combustion coal gangue, etc.). ); ③ Artificial lightweight aggregate (such as expanded perlite, shale ceramsite, clay ceramsite, etc.). ).

2. Technical performance of lightweight aggregate. The technical properties of lightweight aggregate mainly include loose density, strength, particle gradation and water absorption, in addition to durability, volume stability and harmful component content.

(1) loose density: the apparent density of lightweight aggregate directly affects the apparent density and performance of the prepared lightweight aggregate concrete. According to the loose density, light and coarse aggregates are divided into eight grades: 300, 400, 500, 600, 700, 800, 900, 1000kg/m3. The loose density of light sand is 400 kg/m3.

(2) Strength: The strength of light and coarse aggregates is usually measured by "cylinder pressure method". The compressive strength of cylinder is an index that indirectly reflects the particle strength of lightweight aggregate. For the same kind of lightweight aggregate, the compressive strength of cylinder is often linear with bulk density. However, the compressive strength of cylinder can not reflect the true strength of lightweight aggregate in concrete, so the technical specification also stipulates that the strength of lightweight aggregate is evaluated by strength label. "Cylinder pressure method" and strength label test method can refer to relevant specifications.

(3) Water absorption: The water absorption of lightweight aggregate is generally greater than that of ordinary aggregate, which will significantly affect the workability, water-cement ratio and strength of concrete mixture. When designing the mixture ratio of lightweight aggregate concrete, the additional water consumption must be calculated according to the water absorption rate of lightweight aggregate for one hour. According to the national standard, the water absorption rate of lightweight aggregate in one hour is: the water absorption rate of light sand and natural lightweight coarse aggregate is not specified, and the water absorption rate of other lightweight coarse aggregates should not be greater than 22%.

(4) Maximum particle size and particle gradation: The maximum particle size of lightweight aggregate concrete for thermal insulation and structural insulation should not be greater than 40 mm The lightweight aggregate of lightweight aggregate concrete for structure should not be greater than 20 mm 。

For the grading requirements of light coarse aggregate, the void ratio of natural grading should not be greater than 50%, and the fineness modulus of light sand should not be greater than 4.0. The screen margin greater than 5mm should not be greater than 10%.

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