Rock tailings manufacturing sand is the below 4.75㎜ particle generated after the stone crushing process for concrete aggregate production. It is also named as stone slag or stone chip, and it is one type of manufactured too.
Rock tailings sand is a kind of medium-coarse sand with a 2.8-3.5 fineness modulus, but the particle size gradation focuses on both ends, so its gradation is poor. In addition, the stones are usually processed by jaw crusher in rock quarries whose work principle is putting the stones into the gap between the two pieces of jaw plates, after the extruding, bending, crushing processes, the stones will be crushed. The crushing principle determines the shape of the rock tailings sand with more edges and corners, so when it is used to produce concrete with the same strength degree as natural sand concrete, it is bound to affect the flow, water-retaining cohesiveness properties of the concrete. In order to meet the construction requirements and achieve pumpability, you should add moderate amount bonding materials compared with the equal-sized natural concrete. Due to the differences between the quality of raw rock materials and the processing methods, there are various difference between the grain size gradation, grain shape, stone dust content of the rock tailings are different, especially for the grain gradation, if you don’t do the relative adjustment, the original tailings sand cannot be directly used as concrete aggregate.
The experimental results show that the method of mixing tailings sand and fine sand can make the grain gradation of tailings sand meet the construction standards. The tailings mixed sand used as concrete fine aggregate can increase the water demand of ready mix concrete production. However, by adding the superplasticizer or a high performance water reducing agent, you can also make the concrete mixtures slump reach (180 + 20) mm while keeping the water demand constant, which can get the same construction performance as the medium-course concrete; Using mixed tailings sand instead of natural sand to produce C30 (strength level) concrete can improve the strength of concrete. When the original tailings sand and fine sand ratio is 7: 3, the 28 d intensity of concrete can be increased by 8.7%. Therefore, the physical and mechanical properties of tailings mixed sand concrete can completely meet the construction requirements; The concrete shrinkage value of tailings mixed sand is larger than that of natural sand concrete. However, with the improvement of the gradation and fineness modulus of the mixed tailings sand, its influence on the concrete shrinkage performance shows a gradually decreasing trend.
The use of rock tailings sand instead of natural sand in ready mix concrete production, not only can alleviate the processing problem of stone tailings, but also can help to solve the shortage problems of natural sand, which is beneficial to make full use of existing resources and to realize a win-win situation between environmental protection and economical benefit.