Influence Of Fly Ash And Tailings Sand On The Performance Of Aqueduct Concrete And Its Mix Ratio Optimization

Aqueduct is an important water conveyance structure in north China,which plays a positive role in local economic development and ecological protection.However,due to the huge temperature difference and freeze-thaw cycle,the concrete structure of the aqueduct cracked and its durability was reduced,which seriously affected the service life of the aqueduct and its normal economic benefits.At present,China’s rapid industrial development has produced a large number of industrial waste residue,how to improve the utilization rate of industrial waste residue has become an important problem to be solved urgently.Based on this,this paper carried out a study on the performance improvement of aqueduct concrete by using fly ash and tailings.The mechanical properties,failure process and thermal conductivity of concrete test blocks with different replacement rates of fly ash and tailings are studied.The quality loss of concrete and the change of relative moving mould during freeze-thaw cycle;Formula prediction of the optimal fit ratio and each performance of aqueduct concrete under the modeling of response surface method.It is expected to make full use of tailings,fly ash and other waste slag and provide some theoretical basis for the preparation of high-performance green and ecological aqueduct concrete.The main research contents are as follows:(1)Uniaxial compression tests were carried out on test blocks with different fly ash content and tailing sand content respectively.The results showed that with the increase of pulverized coal content,the compressive strength of concrete test blocks at the age of 3d and 7d continued to decrease,and the compressive strength at the age of 28 d first increased and then decreased,reaching the maximum value at the content of 20%.With the increase of the content of tailing sand,the compressive strength of concrete at 3d age continues to decrease.The compressive strength of concrete at 7d and 28 d increases first and then decreases,reaching the maximum value at 25% and 50% of the content respectively.(2)Uniaxial compression tests were carried out on the orthogonal test blocks,and it was found that the relationship between the factors influencing the compressive strength of concrete in 7d and 28 d was the addition amount of fly ash > aggregate particle size > tailing sand.The optimal ratio of compressive strength in 7d was the fly ash substitution rate of 10%,the tailings sand substitution rate of 0%,and the aggregate particle size of 20-25 mm.The optimal ratio of 28 d compressive strength is fly ash replacement rate of 10%,tailing sand replacement rate of 50%,aggregate particle size of 15-20mm;(3)VIC-3D(Digital Image Correlation 3 Dimensions)technique was used to monitor the strain in the failure process of the sample and analyze the crack generation and crack state of the concrete.The results showed that the strain area of the test block with fly ash substitution rate of 10%,tailing sand content of 25% and 50% was concentrated in the sample,with less crack generation and strong crack resistance.(4)Through the rapid freezing-thawing cycle test,the optimal combination of the ratio with the lowest mass loss rate and the slowest relative dynamic elastic modulus decline of the test block is obtained: the replacement rate of fly ash is 10%,the replacement rate of tailings is 50%,and the particle size of aggregate is 15-20 mm.Through the thermal conductivity test,it is found that the fly ash content is the most significant factor affecting the thermal conductivity,and the optimal level for it to reach the maximum value is the fly ash replacement rate of 20%,the tailings replacement rate of 50%,and the aggregate particle size of 5-15 mm.(5)The response surface method is used to establish a regression model to optimize the performance of the aqueduct concrete and obtain the prediction formulas of the concrete’s compressive strength,thermal conductivity and relative dynamic elastic modulus.The optimal ratio of industrial waste residue to meet the performance indexes of aqueduct concrete is the replacement rate of fly ash 7.55%,the replacement rate of tailing sand 42.46%,and the particle size of aggregate 15-20 mm.