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Sand and gravel aggregate is loose and granular in shape, and is the main component of building concrete and mortar, which can account for about 60%-75% of the volume of hardened concrete.Because the quality of sand and gravel aggregates directly affects the overall performance of building concrete, the infrastructure industry usually has the following requirements for the quality of sand and gravel aggregates:

1. The surface of the aggregate is clean and contains few harmful impurities, which cannot affect the setting and hardening of concrete and the durability of concrete in the 

later stage;

2. It should have good particle grading and low porosity, which is conducive to the adjustment of admixture performance and the improvement of concrete performance;

3. Whether it is natural sand aggregate or machine-made sand aggregate, it should have good strength and firmness in order to play the role of skeleton force transmission;

4. In the process of stone mining, it should be regularly tested for alkali activity. If there is a potential danger, corresponding measures should be taken, and it should be proved by professional tests;

5. Sand and gravel aggregates should have good firmness and low water absorption, which should not exceed 3.2, otherwise it will easily lead to concrete cracking.

Characteristics of qualified sand and gravel aggregate

1. The content of harmful impurities should not be higher than 1%, the content of mud lumps should not be higher than 1%, and the content of mud should not exceed 3%;

2. The sand and gravel aggregate particles are full in shape and are cubic, without too many needle-like particles, and the content of needle-like particles should not exceed 

15%.

3. The ratio of aggregate compressive strength to concrete strength grade should not be less than 1.5;

4. The gradation of sand and gravel aggregates is reasonable, more than 1.18 and less than 30%; less than 0.15 should be less than 20%; particles of 0.6 and 0.3 should account for 20%-30% respectively.

Characteristics of qualified sand and gravel aggregate

1. The content of harmful impurities should not be higher than 1%, the content of mud lumps should not be higher than 1%, and the content of mud should not exceed 3%;

2. The sand and gravel aggregate particles are full in shape and are cubic, without too many needle-like particles, and the content of needle-like particles should not exceed 

15%.

3. The ratio of aggregate compressive strength to concrete strength grade should not be less than 1.5;

4. The gradation of sand and gravel aggregates is reasonable, more than 1.18 and less than 30%; less than 0.15 should be less than 20%; particles of 0.6 and 0.3 should account for 20%-30% respectively.