Study On Frost Resistance Of High Volume Fly Ash Concrete In Alpine Region

Fly ash,added into concrete as admixture,can reduce the industrial waste residue,at the same time it can play a role in reducing the hydration heat of concrete mixture,reduce early cracking,improve the later strength of concrete and other functions.But there are many different views on the frost resistance of fly ash concrete.In the alpine region,the temperature difference between day and night is large,winter is long in the negative temperature,so mass concrete engineering is easy to crack in the early stage,but sometimes the project must be constructed in winter.In this paper,the frost resistance of high volume fly ash concrete is studied.First of all,in this paper,four factors and three levels orthogonal test was designed for C30 concrete design.Through the analysis of test results of construction concrete workability and compressive strength,optimum parameters of mix design,reached a conclusion that in the design,the sand rate was 38% of the C30 fly ash concrete in cold area,and the dosage of water reducer was 1.3%,units with 165 kg / m3 water and water cement ratio is 0.41.Then,the compressive strength of fly ash concrete with different water cement ratio,different fly ash content and different air entraining agent was analyzed,We draw the following conclusions: the more fly ash in concrete,the greater early strength would decline,and the greater the 28 d ~ 90 d intensity.When the curing time was more than 28 d,the air content in fly ash concrete increased by 1%,the compressive strength was reduced by about 4% to about 6%.Secondly,for the alpine region of concrete subjected to freeze-thaw cycles and longterm continuous failure problems,from the analysis of the failure mechanism of freezing and thawing,through rapid freeze-thaw test,effects of the dosage of air entraining agent on the frost resistance of fly ash were researched.Then,the frost resistance of fly ash concrete with different amount of fly ash and different air entraining agent was analyzed by means of sub micro bubble characteristic parameters.At last,the compressive strength loss law of ordinary concrete and fly ash concrete in cycle of freezing and thawing is analyzed and compared,we draw the following conclusions: The frost resistance of fly ash concrete for 28 days was significantly lower than that of concrete without fly ash,and the frost resistance of fly ash concrete increased significantly with the increase of age.The air gap coefficient of concrete with fly ash content of 60 days is the smallest,and its durability coefficient is the biggest,and the frost resistance is the best.The air entraining agent can effectively improve the frost resistance of fly ash concrete.When the air content is about 5.2%,the coefficient of air bubble spacing is the smallest,and the frost resistance is the best.Finally,the resistance to chloride ion penetration of fly ash concrete with different fly ash content and different air entraining agent was studied by the electric flux test.The results show that prolonging the curing age of concrete is beneficial to improve the resistance to chloride ion penetration.With the increase of fly ash content,the resistance to chloride ion permeability increases first and then decreases,and reaches the best when the dosage is about 45%.With the increase of air content,the chloride ion permeability of fly ash concrete increases first and then decreases.When the content of air is about 5.2%,the permeability of chloride ion is the best.