Study On Performance Of New Concrete With Balls Made By Tailings Powder As Substitute For Coarse Aggregate

With the development of industrialization and the increasing consumption of mineral resources,more and more solid wastes such as tailings are produced by utilizing the mineral resources.Large number of tailings exist in tailings reservoirs,which not only occupy a large amount of land resources,but also cause great pollution and damage to the ecological environment.At the same time,these tailings reservoirs may also have dam breaks and other accidents,which pose a threat to the safety of human life and property.The research on tailings recovery and utilization has become a hot topic.In this paper,the mechanical properties,durability and microstructural properties of a new type of concrete with low activity tailings powder synthesized by artificial tailings ball as coarse aggregate are studied.The main research contents are as follows:(1)According to the national standard,the raw material test of coarse aggregate for tailings ball shows that the tailings ball basically meets the performance requirements of concrete coarse aggregate.The main difference between tailings and natural aggregates is that the strength of tailings ball itself is low,generally as follows about 40 MPa,the density is slightly higher and the water absorption rate is higher.Because it is made by centrifugal rolling process,it is mostly spherical and the particle size is more concentrated,and the void ratio is higher.(2)Using tailings ball coarse aggregate to design concrete mix proportion,the water-binder ratio of 0.5,0.45,0.4,0.35 and 0.3 is determined first,and then the amount of each part is calculated by "absolute volume method".It is found that there is slurry-bone separation in the mixtures in the trial mixing test.Therefore,it is necessary to adjust the sand ratio according to the filling principle and immerse the tailings ball coarse aggregate in advance to compensate for it.Higher water absorption.(3)Through the mechanical properties tests of tailings ball concrete,the cubic compressive strength increases linearly from 34.87 MPa to 51.21 MPa in the process of water-binder ratio decreasing from 0.5 to 0.3,and the measured elastic modulus of concrete of all strength levels is larger than the calculated value;the early strength is higher,the ratio of axial compressive strength to cubic compressive strength is about 84%,and the splitting tensile strength is cubic compressive strength.The strength ranges from 1/11 to 1/13.The relationship between compressive strength and water-binder ratio of tailings ball concrete satisfies the Boromi formula,but the regression coefficient is different from that of natural aggregate.(4)The failure modes of tailings ball concrete are as follows: when the water-binder ratio is large and the bonding force between aggregate and cement matrix is small,the failure modes are mainly the interface spalling between aggregate and cement matrix.When the water-binder ratio is small,the bonding force between aggregate and cement stone increases,while the strength of aggregate itself is low.Therefore,aggregate damage is the main failure mode,and the interfacial spalling damage is reduced.(5)The chloride penetration resistance and carbonization resistance of mineral ball concrete are better,which are consistent with the law of natural aggregate concrete.The durability of these two kinds of concrete increases with the decrease of water-binder ratio.The new concrete has good frost resistance.After 300 freeze-thaw tests,it still retains more than 75% dynamic elastic modulus,the mass loss is less than 0.3%,and the strength retention rate can reach about 90%.However,the frost resistance tends to decrease with the decrease of water-binder ratio.(6)The micro-interface between aggregate and cement paste of tailings ball concrete with different water-binder ratios was observed by scanning electron microscopy.It was found that the range of "interface transition zone" was less than 30 micron.With the decrease of water-binder ratio,the interfacial micro-cracks disappear,the transition zone becomes not obvious,and aggregate and cement matrix become a whole.