Experimental Study On The Frost Resistance Of Fly Ash And Silica Fume Concrete

In the cold region, frost resistance of concrete is often the main factor determining thedurability of concrete. The aging and diseases of hydraulic engineering concretestructure is affected by freeze-thaw damage. It is the key problem to solve frostresistance of concrete in the cold regions hydraulic structure. Currently, highly efficientactive admixtures such as the fly ash and silica fume, is widely applied to hydraulicengineering.The study of the frost resistance influence of hydraulic structure concretewith fly ash and silica fume in cold regions has significance and has a wide foregroundof engineering applications.The status of study on frost resistance of concrete is overviewed, which focuses onthe freeze-thaw damage mechanism and measures to improve frost resistance.Freeze-thaw damage influencing factors are analyzed. Through rapid freezing andthawing test of concrete specimens, the effect of fly ash and silica fume on the frostresistance of hydraulic structure concrete in cold regions is studied. The ultrasonicvelocity of concrete before and after freezing and thawing cycles is studied.Rapid freezing and thawing test of the concrete specimens with different contents offly ash and silica fume. Through the variation analysis of the mass loss rate and therelative elastic modulus, the impact on frost resistance of the different content of fly ashand silica fume is determined, and the optimal dosage of fly ash and silica fume ofdifferent strength concrete is determined. The optimal dosage with silica fume: C20silica fume concrete optimal dosage is12%.The mass loss rate is0.68%after350freezing and thawing cycles, and the relative dynamic modulus is80.3%. C25silicafume concrete optimal dosage is9%. The mass loss rate after350freezing and thawingcycles is0.67%and relative dynamic modulus is86.4%. The optimal fly ash content is15%. After300freezing and thawing cycles, the mass loss rate is less than1.3%, andthe relative dynamic modulus is higher than82%. Fly ash and silica fume complexoptimal dosage is that fly ash content is20%and silica fume is2%, the mass loss rate ofC20concrete is less than1%and the relative move modulus is higher than99%after300freezing and thawing cycles. After650freezing and thawing cycles, the mass lossrate of C25concrete is4.9%. The relative dynamic modulus is85.9%. Simultaneously the ultrasonic velocity of C25double-doped fly ash and silica fume is detected beforeand after freezing and thawing, It is discovered that the ultrasonic velocity will decreaseafter freezing and thawing cycles, the ultrasonic velocity of the concrete which hasoccurred the freeze-thaw damage reduces to less than4.000km/s, and the variationultrasonic velocity is similar to the relative elastic modulus after thawing and changes.The test study shows the frost resistance effects of the hydraulic structure concretewith fly ash and silica fumeon in the cold regions. The optimal dosage of fly ash andsilica fume which has good frost resistance is determined. It has practical significance toimprove the frost durability of hydraulic structural concrete of in cold regions.