How to judge the quality of sand aggregate
The quality of sand and gravel aggregate in sand making plants mainly depends on the mud content, particle gradation, and the strength of sand and gravel.
Sand and gravel aggregates have a large mud content. At present, the mining of river sand is prohibited in many places. Even if there is a supply of river sand, the mud content is relatively large and the quality is poor. Many concrete companies use stone leftovers—stone chips as fine aggregates, and sometimes the stone powder contains an astonishing amount of mud. The fineness modulus of fine aggregate sand varies greatly. Different sources and materials of fine aggregates of sand and gravel aggregates lead to great differences in fineness modulus. There are often multiple suppliers of fine aggregates, and the incoming materials are crossed, which intensifies the fluctuation of fineness modulus of fine aggregates.
Poor gradation of sand and gravel aggregates. The main performance is that the gravel factory sieves the gravel into 5-10mm, 10-25mm and 20-31.5mm grades for sale, and the concrete company uses it alone, resulting in poor gradation. In addition, the small scrap stone chips from the stone factory are often sold to concrete companies as so-called “machine-made sand”. The gradation of the stone chips is mostly “large particles at the two ends and insufficient particles in the middle”, which brings difficulties to the preparation of concrete.
Sand and gravel aggregate material is poor. Aggregate contains a large number of weathered and weak particles, resulting in low crushing value and high water absorption. On the one hand, the work performance of the concrete mixture is deteriorated, and on the other hand, the strength of the concrete is low and the durability is deteriorated. Aggregate particle shape is poor. Affected by the material of the aggregate parent rock and the production process, the content of needle flake particles in the aggregate 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.