Experimental Study For Freeze-Thaw And Corrosion Of Fly Ash Concrete

As one of the most widely used building materials, the concrete and its economy and durability have been paid more and more attention. In this paper, high strength concrete was made by mixing with a certain proportion of grade II fly ash. Then mechanical properties of fly ash concrete under the condition of freeze-thaw, sulphate and acid corrosion were studied to explore the influence of cold weather and corrosion substances on fly ash's strength and mechanism of freeze-thaw and corrosion was analyzed. This study is of great practical significance to the utilization of fly ash in industrial waste, the reducing of environmental pollution, as well as the application of fly ash concrete in the circumstances of freezing and thawing and corrosion. The main jobs include:Firstly, the class II fly ash concrete was tried to be compound by selecting multiple sets of water-cement ratio. Through lots of experiments, the test selected the best water-cement ratio and proved that class II fly ash can be compound to concrete with its compressive strength C45.Secondly, the test made concretes whose class II fly ash contents were respectively 0%, 10%, 18%, 25%, and tested their compressive strength after 28ds and 120ds. The results showed that with age increases, the addition of fly ash concrete's strength was more than ordinary one's, and at the same conditions of strength grade, the greater the amount of fly ash was, the higher the latter intensity of concrete containing 0%～25% quantity fly ash became.Thirdly, the specimen was frozen by gas and melted by liquid with different concentration rate of Na₂SO₄ and HCl solution as the melts medium, respectively went through 50, 70,100,150 times corrosion freeze-thaw cycles. Then the impact of times of freeze-thaw cycle, amount of fly ash and concentration of corrosion solution on concrete's strength were analyzed. The experimental results indicate that the strength of concrete declined after freeze-thaw and corrosion cycle, the compressive strength of fly ash concrete increased first then decreased with freeze-thaw and corrosion cycle, the curve was different from the ordinary concrete whose strength declined constantly. Thus it indicated that the impact of freeze-thaw and corrosion on the strength of fly ash concrete was lower compared with ordinary ones. At the same time, to the fly-ash concrete experiencing the same freeze-thaw and corrosion cycles, reducing of compressive strength was inversely proportional with the content of fly ash and was directly proportional to the concentration of corrosion solution.Finally, damage mechanism and mass loss of fly ash concrete under the coupling action of freezing and thawing and corrosion were analyzed. The research of this article provides important reference material for fly ash concrete's design and application in the north cold area.