Study On The Mix Design And Performance Of Mechanized Sand Concrete With Iron Tailings

In the past,natural river sand,as the main fine aggregate in concrete,played a vital role in the construction of infrastructure.With the rapid development of our urbanization process,the demand for concrete is surging,but natural river sand resources are facing exhaustion,natural river sand is a non-renewable resource,which is not renewable in a short time,excessive exploitation will break the ecological balance,bring serious impact on the surrounding environment.As an industrial solid waste produced after beneficiation,the reserves of iron tailings are constantly increasing.The accumulation of a large number of iron tailings not only wastes land resources,but also greatly damages the ecological environment of mines.The comprehensive utilization of iron tailings is bound to become an important means to improve the utilization efficiency of solid waste,and the processing of iron tailings into machine sand for concrete is a feasible waste benefit measure.It can not only solve the contradiction between supply and demand of construction sand,but also promote the application of machine-made sand in engineering construction.However,due to the lithology of tailings base material,sand making equipment and technology and other factors,the performance difference between iron tailings machine-made sand and natural river sand is significant.The machine-made sand concrete prepared according to the current specifications cannot meet the actual engineering requirements.Therefore,the existing concrete mix design method should be improved to ensure that the iron-tailings machine-made sand concrete can meet the engineering needs.Based on the above problems,this paper selects three concrete mix design methods to design the concrete mix of iron tailings machine-made sand,and conducts a comparative analysis on the design results to obtain the benchmark mix.On this basis,the influence law of water-binder ratio,sand rate and mineral admixture dosage on the performance of iron tailings machine-made sand concrete is studied,and the optimal range value is obtained.Realize the optimization of configuration parameters.By analyzing the characteristics of iron tailings mechanical sand,the effects of iron tailings mechanical sand gradation,stone powder content and sulfur content on the performance of concrete were studied,and the improvement measures were put forward.In this paper,the mix design method based on saturated surface dry aggregate,concrete mix design method based on raw material performance and common concrete mix design method are used to design C30,C40 and C50 iron tailings mechanical sand concrete,and the comparison test is carried out.The test results show that the concrete designed by raw material method takes into account the quality of iron tailings mechanical sand.The calculated sand rate is reasonable,the overall working performance is excellent,the compressive strength can meet the design requirements,reflecting good volume stability and durability.The working performance of standard method and saturated surface dry method is poor in low strength grade concrete,while the performance is better in medium and high strength grade concrete with excellent technical indexes of machine-made sand.Therefore,the raw material method is more suitable for the design of machine-made sand concrete with iron tailings.The influence law of water-binder ratio,sand rate and mineral admixture amount on the performance of iron tailings machine-made sand concrete was explored,and the appropriate range of these parameters was determined by comparing with river sand concrete,and the iron tailings machine-made sand concrete was prepared with the same working performance as river sand concrete,and the 28 d compressive strength was higher than river sand concrete.The suitable range of water-binder ratio of concrete with C30 iron tailings is 0.44～0.48,sand rate is 43%～45%,and the suitable content of fly ash and mineral powder is 20%:30%,respectively;The suitable range of water-binder ratio of concrete with C40 iron tailings is0.40～0.44,sand rate is 41%～45%,and the suitable content of fly ash and mineral powder is25%:20%,respectively.The suitable range of water-binder ratio of concrete with C50 iron tailings is 0.34～0.38,sand rate is 38%～42%,and the suitable content of fly ash and mineral powder is 20%:15%,respectively.The influence of mechanical sand properties of iron tailings on concrete properties was investigated.The mechanical sand grade of iron tailings has a significant influence on the concrete.The particle content of mechanical sand above 1.18 mm should be controlled between 25% and 35%,the particle content of 1.18 mm to 0.3mm should be controlled between 50% and 60%,and the particle content of less than 0.3mm should be controlled between 10% and 25%.It is beneficial to the development of working and mechanical properties.Appropriate amount of stone powder in iron tailings machine-made sand can improve the work and mechanical properties of concrete.For C30,C40 and C50 concrete,the optimal content range of stone powder in iron tailings machine-made sand is 9%～12%,6%～12% and 6%～9%,respectively.Compared with the reference group,iron tailings powder can effectively improve the mechanical properties of concrete,improve the chloride ion penetration resistance and freeze resistance.Through X-ray diffraction,mercury injection test and field emission electron scanning microscope,the influence rule of sulfur content in mechanical sand on concrete performance was studied.The increase of sulfur content led to the increase of gypsum and AFt crystal content in sulfur bearing mortar specimens,and a large amount of AFt would cause concrete expansion cracking and reduce the mechanical pproperties of iron tailings machine made sand concrete.