| With the rapid development of the engineering industry,a large amount of cement concrete is used in building construction.Cement production has caused great damage to the environment,high-volume fly ash concrete can not only reduce the amount of cement,but also the waste generated by the thermal power plant-fly ash as a concrete admixture to be used,this application reduces the pollution of the environment,but also saves the cost of the project,which has a broad application space.In recent years,due to the objective conditions such as duration,more and more mass concrete structures are constructed in winter,after concrete molding,the concrete subjected to early frostbite,its performance decreased significantly.Therefore,it is urgent to study the performance of high-volume fly ash concrete under negative temperature,in this paper,a series of studies on the mechanical properties and durability of high-volume fly ash concrete in alpine region,which have a certain value.First of all,this paper is aimed at the mechanical properties of high-volume fly ash concrete,which using three kinds of water-binder ratio and five kinds of content of fly ash.The compressive strength,splitting tensile strength and flexural strength of different age were tested,and the mechanical properties were analyzed.The results show: the main factors influencing the strength of concrete with large amount of fly ash are water-cement ratio,and the effect of fly ash content on compressive strength is more sensitive than other mechanical properties;with the increase of content of fly ash,the early mechanical properties of fresh concrete are significantly reduced,but the late growth is rapid and the content of fly ash is less than 35%,the mechanical properties of 90 d are not lower than that of ordinary concrete.Secondly,resistant freezing critical strength of minus temperature concrete is obtained by compressive strength guarantee rate.The compressive strength of 18 h ~ 48 h and 60 d were measured by using four kinds of concrete with water and cement ratio of 0.4,fly ash content of 25%,35%,45% and 55% respectively;After the early formation of minus temperature concrete subjected to different frozen system,and then transferred to standard maintenance,to test its 60 d compressive strength can reach the standard curing concrete corresponding to the age of compressive strength of 95%,and the pre-curing age and the final compressive strength were linearly fitted to obtain the resistant freezing critical strength of minus temperature concrete,and then the influence of the fly ash content and the freezing system on the frozen critical strength of the concrete was analyzed.The results show that the fly ash content increases and resistant freezing critical strength decreases,in the degree of damage to the damage: constant negative temperature freezing of gas<multiple freeze-thaw cycles<constant negative temperature freezing of water.Finally,in this paper,the influence of the concrete on the durability of the concrete after its resistant freezing critical strength is analyzed.Using rapid freezing and thawing method and anti-permeability test,testing the minus temperature of the concrete freeze-thaw cycle times and the amount of electricity can reach the standard conservation group 95%.The experimental results show that the antifreeze critical strength determined by the compressive strength guarantee rate does not make the frost resistance of 95%,on the durability requirements of the structure,should be appropriate to extend its pre-frozen pre-curing time,the construction of large-volume structures in winter concrete recommended fly ash content of 35%.At the same time,this paper also uses the bubble spacing coefficient analyzer to analyze the bubble structure of high volume fly ash concrete,it is found that the number of bubbles increases with the increase of fly ash content.It is suggested that the c high-volume fly ash concrete of evaluating the bubble parameters should be evaluated after 60 days. |
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