Study On The Influence Of Natural Sand On The Mechanical Properties And Durability Of Asphalt Concrete Core Wall

Asphalt concrete core wall dam has been widely used in water conservancy and hydropower projects because of its excellent impermeability and adaptability to uneven settlement of earth-rock dam.However,the research on the raw material of asphalt concrete with core wall is still insufficient.Based on a RCC core dam project under construction in Xinjiang,this paper selects typical natural sand and artificial sand based on the optimized mix ratio of the project,and explores the influence of natural sand on the related properties of core asphalt concrete through laboratory tests under the same mix ratio.Based on the existing water stability test methods,extend the soaking specimens of soaking time and increased temperature,at the same time,rules and regulations of the compressive strength of water stability factor evaluation index on the basis of increased flooding bending strain ratio and soaking splitting strength ratio evaluation index,analysis of the influence of natural sand has good performance of asphalt concrete wall;The durability model of core wall asphalt concrete was established according to the durability test data combined with time-temperature equivalence principle and Boltzmann function model,and the durability performance of core wall asphalt concrete prepared with two kinds of fine aggregate was analyzed and evaluated.The main conclusions are as follows:(1)Because natural sand has smooth surface,relatively weak bonding ability with asphalt,and can generate more free asphalt when asphalt concrete is mixed and formed,under the same mixture ratio,At the same compaction temperature and times,the decreasing percentage of porosity of Mashel specimens prepared with natural sand is 8.0%～14.1% and 0.7%～6.9% higher than that of artificial sand,respectively,which shows that natural sand has obvious improvement effect on the workability of asphalt concrete with core wall,and its mixture has strong adaptability to temperature change.(2)In the same mix ratio,the core wall asphalt concrete prepared by two kinds of fine aggregate has its own advantages and disadvantages,and can meet the requirements of the code.The compressive strength strain,tensile strain and bending strain of asphalt concrete prepared with natural sand are 9.1%,15.2% and33.4% higher than those made with artificial sand,respectively.It shows that natural sand can improve the deformation ability of asphalt concrete with core wall.(3)With the increase of soaking temperature and soaking time,the use of natural sand core wall of asphalt concrete’s durability evaluation index attenuation faster than artificial sand,show the natural sand core wall of water damage of asphalt concrete is weak,durable performance is poorer,and the evaluation index of asphalt concrete durability of the heart wall,The attenuation rate is the fastest bending strain ratio and the water stability coefficient of compressive strength is the slowest.(4)Scholars of the former Soviet Union have proposed that asphalt concrete soaked in water of 80℃for 75 hours is equivalent to the equivalent relationship of soaking in water of 20℃ for 1 year.However,according to the research in this paper,different asphalt mixtures and even different specimen sizes will have different stress and strain attenuation acceleration coefficients,which cannot be generalized.(5)The compressive water stability coefficient of asphalt concrete specimens with two kinds of fine aggregate after being immersed in water at 60℃ for 48 hours is 0.998 and 0.996,respectively;After soaking in water at 60℃ for 24 hours,the splits strength ratios were 0.983 and 1.006,respectively,which could meet the requirements of the specification.However,from the perspective of long-term performance,both the compressive water stability coefficient and the water-immersion splitting strength ratio have dropped below the evaluation index values specified in the code.Therefore,it is not appropriate to take 0.90 and0.70 as the lower limit index value to evaluate durability.(6)Since there is currently no specification for the evaluation index value of immersion bending strain ratio,when the lower limit index value of bending strain is used as the durability evaluation index of core wall asphalt concrete,the bending strain value of two kinds of fine aggregate prepared by soaking in water at 80℃ for 70 d is 1.670% and 3.119%,respectively.All meet the requirements of more than 1% in the specification.The test results show that natural sand can be used as fine aggregate for core wall asphalt concrete,which can meet the requirements of performance evaluation index in the existing code.