Study On Carbonation Performance Of Fly Ash Concrete Under Freezing-thawing-wet-dry Cycle Coupling Damage

The durability damage of fly ash concrete structures is not caused by a single factor alone,but is regulated by two or more factors.In North China,buildings are not only eroded by carbon dioxide,but also freeze-thaw cycles occur frequently during the summer rainy season.As a result,buildings suffer severe dry and wet cycle damage and freeze-thaw cycle damage.Based on this,this paper designs a complete set of test plan and carries out the study of durability damage test under the influence of three factors.The effects of freeze-thaw cycle damage or dry-wet cycle damage on the carbonation performance of fly ash concrete,and the effects of freeze-thaw cycles and wet-dry cycle coupling on the carbonation performance of fly ash concrete were discussed.This paper selects four groups of fly ash concrete with fly ash content of 0%,10%,20%,and 30%.The main tests are: single freeze-thaw cycle test,single dry-wet cycle test and freeze-thaw cycle.Wet and dry cycle tests were conducted to study the effects of three damage modes on the dynamic elastic modulus and mass loss rate of fly ash concrete with different contents.Cycle tests were used to study the freeze-thaw cycle,dry-wet cycle and freeze-thaw cycle.Effect of Carbonation Performance of Fly Ash Concrete with Four Additives.The analysis results show that the dynamic elastic modulus and mass loss rate of concrete under three kinds of damages show a trend of first slight increase and then gradually decrease;the total damage degree of freeze-thaw-wet-wet cycle is much greater than the simple superposition of each single damage degree.Each damage factor is a negative damage effect relationship,that is,one damage factor accelerates the damage effect of another damage factor,or both accelerate injury;when the concrete’s elastic modulus reaches the same degree of damage in three damage modes,freeze-thaw-dry-wet cycle damage is 1.3 times that of the freeze-thaw cycle,3.8 times that of the wet-dry cycle;the analysis of concrete carbonation depth and test cycle times under different damage modes shows that when reaching a certain carbonization depth The freeze-thaw-dry-wet-carbonization model requires the least amount of time,the freeze-thaw-carbonization cycle takes the second place,and the dry-wet-carbonization cycle takes the longest;establishing a modified fly ash concrete under freeze-thaw-dry-wet cycle damage The carbonation model can provide some technical guidance for the analysis of carbonation properties of fly ash concrete.