(1) The aggregate has a large mud content. At present, mining of river sand is prohibited in many places. Even if there is river sand supply, the mud content is too large and the quality is poor. Many concrete companies use stone scraps-stone chips as fine aggregate, and sometimes the amount of mud in stone powder is staggering.

(2) Poor aggregate gradation. It is mainly manifested in the fact that the gravel sieves are divided into 5-10mm, 10-25mm and 20-31.5mm grades, and the concrete enterprises use it alone to cause gradation difference. In addition, the small scraps of stone chips in the stone factory are often sold as so-called "mechanical sand" to concrete companies. The gradation of stone chips is mostly "large particle content at both ends and insufficient particles in the middle", which makes it difficult to prepare concrete.

(3) The fineness modulus of fine aggregate sand varies greatly. The different sources and materials of fine aggregates result in great differences in fineness modulus. Concrete companies often have multiple fine aggregate suppliers, and the incoming materials cross over, exacerbating the fluctuation of fine aggregate modulus.

(4) Poor aggregate material. Aggregate contains a large amount of weathered and weak particles, resulting in low crushing value and high water absorption rate. On the one hand, the workability of the concrete mixture is deteriorated, on the other hand, the concrete strength is low, and the durability is deteriorated.

(5) Poor aggregate shape. Affected by the material and production process of aggregate mother rock, the content of aggregate needle flake particles is relatively high. Although some particles do not meet the needle flake specifications, the irregular particle shape leads to poor workability and mechanical properties of concrete.

Strengthening sand and gravel inspection is the key material to control aggregate quality

The quality of the fine aggregate is preliminarily determined by the "experience + test" method, with experience supplemented by the test.