Study On Impermeability Of High Volume Iron Ore Tailings Sand Concrete

With the development and optimization of material properties in the construction industry,in order to solve the environmental problems caused by the accumulation of a large number of tailings,many scholars have used iron tailings to replace some fine aggregates to prepare mixed aggregate concrete.It can not only solve the shortage of natural sand,but also improve the comprehensive utilization rate of solid waste.At present,scholars have done a lot of research in this field,but the content of iron tailings is still generally low,and there are many studies on mechanical properties and few studies on impermeability.In order to improve the content of iron tailings and the comprehensive utilization rate of solid waste,this thesis studies the concrete with large amount of iron tailings sand and its impermeability through experiments.The mineral composition of the active material was analyzed by XRD,and the microstructure and hydration products of iron tailings sand composite aggregate concrete were studied by SEM.The main research contents and conclusions are as follows :(1)The effects of water-binder ratio,iron tailings sand content and percentage of sand on the impermeability of iron tailings sand composite aggregate concrete were studied through experiments.The results show that the water-binder ratio is the main influencing factor affecting the change of impermeability of concrete,followed by the amount of iron tailings sand,and then the percentage of sand.The impermeability of concrete increases first and then decreases with the increase of water-binder ratio.With the increase of iron tailings sand replacement rate,it decreases first,then increases and then decreases.When the water-binder ratio is 0.5 and the percentage of sand is 40%,the impermeability grade of the composite aggregate concrete reaches the best.The optimal iron tailings sand content is increased to 50%,and the impermeability grade is54% higher than that of the concrete with 20% iron tailings.Therefore,appropriate water-binder ratio and percentage of sand can not only increase the iron tailings content of concrete but also improve the impermeability.(2)The mineral composition of cementitious materials was analyzed by XRD.The results show that the mineral composition of cement is mainly tricalcium silicate,dicalcium silicate,tricalcium aluminate and tetracalcium aluminoferrate;the mineral composition of silica fume is mainly silica,which provides pozzolanic activity and promotes hydration of materials;the mineral composition of iron tailings mainly includes silica,plagioclase,hematite and calcite.The micro-test of the optimal group and the worst group of impermeability was carried out by SEM.The results show that the hydration products are mainly acicular ettringite,tabular calcium hydroxide and hydrated calcium silicate gel.As the replacement rate of iron tailings sand increases from 50 % to 70 %,the number of internal pores increases,the amount of gel hydration products decreases sharply,and the micro cracks and pores near interfacial transition zone increase.The internal density of concrete decreases,some water passages are not fully filled,and the impermeability of concrete decreases linearly.Therefore,in terms of meso-structure,the number and size of internal pores,the amount of hydration products and the compactness of interfacial transition zone can affect the impermeability of concrete.(3)The research results show that by controlling the reasonable water-binder ratio,percentage of sand and slurry-bone ratio,a larger percentage of sand can be used to increase the proportion of iron tailings in the total mass of concrete,which can meet the general impermeability requirements and appropriate cost performance of the project.This thesis innovatively improves the optimal dosage of iron tailings in iron tailings sand impermeability concrete,and its performance is good.In addition,in the impermeability test,it is found that the existing sealing method can not be easily and effectively sealed.After repeated exploration and summary,the traditional butter plus cement method has been improved,and its sealing effect is good.