| China has a vast territory with a large north-south span,and significant differences in climate change.The northern region experiences long periods of low temperature and freezing weather every year,especially in the cold and arid regions of northwest my country,where low temperature weather occurs for about half of the time.Taken into account the limitations of water conservancy project construction,it is necessary to carry out construction during the period of no or little water in winter,which undoubtedly increases the difficulty of construction.In addition,the weather in the northwest region is changeable and the temperature difference between day and night is large.No antifreeze is added or the antifreeze protection work during the construction period of the concrete structure is not done well,so that the concrete in the initial setting or curing period appears early freezing,which affects the hydration process of the concrete,delays the process of concrete reaching the critical strength,and even the concrete Permanent damage to the structure greatly reduces the service life of the concrete and the practical value of the project.Aimed at the problems of premature cracking and peeling of early frozen concrete in the later service process,and the deterioration of later service materials under the salt and freezing erosion environment,the results were obtained through on-site investigation of hydraulic structures in the cold and arid areas of northwestern China,and water and soil samples were collected for inspection.The corrosive medium is analyzed,the working environment of the concrete structure is analyzed,and the corresponding indoor accelerated test is designed to determine the curing conditions for the most severe damage to the early-freezing concrete.Analyze the frost resistance durability of concrete under different mix ratios.By collecting data such as mass loss rate,relative dynamic elastic modulus,compressive strength,ultrasonic wave velocity and pore size distribution,it is concluded that changing the mix ratio has an effect on the deterioration of early-freezing concrete durability.Influence,and then get the best mix ratio.Based on the RSM response model,the concrete compressive strength is regression fitting,and the best mix ratio is found by statistical methods.The main conclusions of this paper are as follows:(1)Under the influence of different freezing temperatures,the order of durability is:-10℃early-freezing concrete<-5℃ early-freezing concrete;under the conditions of different freezing moments,the durability ranking is: 3.5h<1h <8h<24h< have not been frozen in the previous period.(2)The water-binder ratio and air content greatly affect the durability of early-frozen concrete.Adding fly ash is not good for the early strength of concrete,but it improves the durability of early-frozen concrete after the freeze-thaw cycle.The experiment shows that the best mixing ratio is: water-binder ratio 0.35,fly ash content 20%,and air-entraining agent0.01%.(3)The water-binder ratio,air content and fly ash have significant effects on the pores of concrete.The larger the water-binder ratio,the more the larger the internal pores.With the addition of fly ash,the internal space is dense,thereby reducing harmful effects.The number of holes;the increase in air content is conducive to improving the internal pores,thereby enhancing the frost resistance and durability of concrete.According to the results,the best mixing ratio is 0.35 water-binder ratio,20% fly ash content,and 0.01% air-entraining agent content.(4)Accorded to the RSM response model to analyze the 28 d compressive strength of concrete,it can be seen that the best mix ratio to improve the durability of early-freeze concrete is 0.35 water-binder ratio,20% fly ash content,and 0.01% air-entraining agent content.Among the single factors that affect the compressive strength,the significant degree is water-binder ratio> fly ash content> air-entraining amount;in the two-factor interaction that affects compressive strength,the significant degree is water-binder ratio and The amount of fly ash>the amount of fly ash and the amount of air-entraining agent>the water-binder ratio and the amount of air-entraining agent.In this paper,through a rigorous and appropriate indoor accelerated test,the decay process of the frost resistance durability of early frozen concrete materials under the influence of waterbinder ratio,fly ash and air-entraining agent is studied,and it is verified by statistical methods.The best mix ratio can provide a reference for the construction of hydraulic structures in cold and arid areas. |
