Artificial aggregate is artificial sand and stone materials crushed and grinded from rocks with mechanical method. As for the raw materials of artificial sand and stone materials, the rock type is unitary and the configuration is controllable, for this reason, the quarrying production can be carried out throughout the year, and it brings little harm to the environment. Therefore, it is more and more widely used by people both at home and abroad. Artificial coarse aggregate is usually called crushing stone whose particle shape is mainly affected by the lithology of raw stone and the model of crusher. Generally speaking, the particle shape of crushing stone made by limestone and granite is good, while the content of needle-shaped particles is high in crushed stone made by basalt and quartzite. Crushing stone produced by hammer crusher has square particle shape, while jaw crusher produces more needle flake particles which largely gather in fine stone. Artificial sand produced by rod mill is relatively ideal in both particle shape and grading. Once material source of artificial aggregate is selected, we need to adopt proper technological process and equipment to produce high-quality aggregate.
Artificial aggregate is rough in surface and has rich edges. It has a good bonding performance with set cement. Concrete produced by gravel has higher tensile strength. If limestone crushing stone is used to mix and produce concrete, linear expansion coefficient can be lowered, which is beneficial to temperature controlling. But compared with crushing stone whose surface is smooth and rounded, the porosity of concrete made by limestone crushing stone is about 0 ~ 11% higher. Thus more cement mortar is needed to fill it, that is, higher sand ratio and more cement are needed. In addition, the specific surface area of crushing stone is big and from the perspective of wet package surface, more cement mortar is also needed to achieve good workability.
Both natural aggregate and artificial aggregate require good grading. Grading is to assort aggregate of different particle diameter according to certain proportion. Therefore, original mixed aggregates need to be divided into several particle size grades, and generally screening machine, hydraulic classifier and mechanical classifier are used to grade them. Neither screening nor grading is able to completely separate aggregate according to the size of demarcation boundary. Some aggregates whose particle size is smaller than that of demarcation boundary is left on the screen and become ponysize aggregate, while aggregates whose particle size is bigger than that of demarcation boundary mixes with next-procedure product and become oversize aggregate. All these ponysize aggregates and oversize aggregates actually change the scheduled grades of aggregates.
