Study On Properties And Frost Resistance Of Molybdenum Tailings Powder Modified Hydraulic Concrete

In recent years,with the rapid development of China’s economy,the exploitation and treatment of molybdenum tailings have also increased.The accumulation of tailings materials has led to the occupation of a large amount of land resources and environmental pollution.In addition,there are many thermal power plants in northern China,which leads to the shortage of fly ash in southern China due to transportation problems.Due to the particularity of its use environment,the temperature and humidity of hydraulic structures are different from those of ordinary buildings,especially in cold areas.The service life of common hydraulic dams will be seriously affected in the cold plateau environment.In view of the above problems,this paper intends to use molybdenum tailings instead of fly ash to prepare modified hydraulic concrete,which provides basic research for solving the dual problems of difficult storage of molybdenum tailings and shortage of raw materials for hydraulic concrete in cold regions,and realizes the resource utilization of solid waste.In this paper,concrete specimens were prepared by replacing fly ash with different contents（0%,10%,20%,25%and 30%）of molybdenum tailings powder.The cubic compressive strength test of molybdenum tailings hydraulic concrete under different standard curing ages（1d,7d,14d,28d and 45d）,the frost resistance test of molybdenum tailings hydraulic concrete under different freeze-thaw cycles（0 times,50 times,100 times,150 times,175 times and 200 times）,and the industrial CT scan after different freeze-thaw cycles（0times,50 times,100 times and 150 times）nondestructive testing.Based on the above experiments,the evaluation indexes of concrete compressive strength,mass loss,relative dynamic elastic modulus loss,porosity and pore volume distribution are discussed and analyzed,and the following conclusions are drawn:（1）Based on the cubic compressive strength test of concrete prepared by molybdenum tailings powder instead of fly ash,the effects of different curing ages and molybdenum tailings content on the compressive strength of concrete were studied.The results show that in the same standard curing age,the cubic compressive strength of molybdenum tailings hydraulic concrete increases first and then decreases with the increase of molybdenum tailings content,and the cubic compressive strength of concrete in the four experimental groups is higher than that of the control group RC（0%）at the same age.Under the same molybdenum tailings content,the growth rate of concrete cube compressive strength increased first and then decreased.Combined with the cubic compressive strength of concrete at each standard age,it can be found that the cubic compressive strength of M₂₀C（20%）concrete in the experimental group with 20%molybdenum tailings is at the highest level.Therefore,in terms of concrete cube compressive strength index,the optimal content of molybdenum tailings is 20%.（2）Based on the rapid freeze-thaw cycle test of concrete prepared by molybdenum tailings powder instead of fly ash,the effects of different freeze-thaw cycles and molybdenum tailings content on the frost resistance of concrete were studied by two indexes of mass loss and relative dynamic elastic modulus.With the increase of the number of freeze-thaw cycles,the quality of the molybdenum tailings hydraulic concrete test block gradually decreased,and the quality decreased rapidly after 100 freeze-thaw cycles.The mass loss rate decreases first and then increases with the increase of molybdenum tailings content.The relative dynamic elastic modulus of molybdenum tailings hydraulic concrete decreases gradually with the increase of freeze-thaw cycles.The relative dynamic elastic modulus of molybdenum tailings hydraulic concrete decreases first and then increases with the increase of molybdenum tailings content,and decreases slowly in the early stage of freeze-thaw cycle test and decreases rapidly in the later stage.Therefore,the index of frost resistance of concrete quality loss and relative dynamic elastic modulus loss point of view,molybdenum tailings optimal dosage is 20%.（3）Based on the preparation of concrete by replacing fly ash with molybdenum tailings powder,the industrial CT scanning test was carried out on the molybdenum tailings hydraulic concrete specimens after 0,50,100 and 150 freeze-thaw cycles to study the internal structure evolution.The results show that the overall change trend of the porosity of the molybdenum tailings hydraulic concrete specimens is consistent,which gradually increases with the increase of the number of freeze-thaw cycles,and the change rate of the pore volume is also accelerated.Under the same number of freeze-thaw cycles,the porosity of concrete specimens with the increase of molybdenum tailings content decreased first and then increased,and the porosity of concrete specimens with the maximum molybdenum tailings content is less than that without molybdenum tailings.The proportion of pore volume that（≤0.01mm³,0.01-0.1mm³,0.1-1mm³ and 1-10mm³）of molybdenum tailings hydraulic concrete is relatively small,while the proportion of pore volume（>10mm³）is relatively large,indicating that the incorporation of molybdenum tailings can reduce the porosity of concrete specimens.Through the above research,the effects of different amounts of molybdenum tailings powder on the mechanical properties and freeze-thaw deterioration of concrete during curing are comprehensively analyzed.In this paper,the optimal amount of molybdenum tailings is20%.The optimum content of molybdenum tailings concrete was revealed by experimental research,which provided a theoretical and application basis for solving the problem of tailings accumulation and realizing the recycling of tailings resources to reduce the frost damage of concrete in cold regions,and obtained a new type of building material.