Effect Of Carbonated Fly Ash And Carbonation Curing On Strength And Permeability Of Cement Mortar

In order to improve the utilization rate of fly ash and reduce the pressure of carbon emission on the environment,this paper first uses fly ash to fix carbon,then adds carbonated fly ash into cement-based materials,and carries out standard curing and carbonation curing,so as to explore the feasibility of carbonated fly ash in cement-based materials.In this paper,the carbon absorption efficiency of low and high calcium fly ash,as well as the influence on its activity,phase composition and morphology before and after carbonation,were studied under different carbonization time(2h,4h)and different water-solid ratio(0.1,0.15,0.2).It was found that the content of calcium carbonate increased significantly after carbonation,and the morphology changed,and the carbon absorption efficiency of high calcium fly ash was much higher than that of low carbon fly ash,up to 5.12%,while the activity of fly ash before and after carbonization is not affected.In addition,carbonated fly ash can accelerate the hydration process of cement and promote the appearance of exothermic peak.Therefore,carbonated fly ash has a certain potential in the application of cement-based materials.Then,the effects of different water binder ratios(0.3,0.4,0.5)and different contents(10%,20% and 30%)of carbonated high calcium fly ash and 30%carbonated low calcium fly ash on the fluidity,mechanical properties,impermeability and chloride ion permeability of cement mortar were studied.It is found that carbonated fly ash can slightly reduce the fluidity of cement compared with non carbonized fly ash,and the decrease range is obvious with the decrease of water binder ratio.The results show that the addition of carbonated fly ash can improve the early strength of cement mortar,slightly reduce the 28 d strength of the specimen,and obviously enhance the 56 d compressive strength;while the capillary water absorption and electric flux of the cement mortar with carbonated fly ash increase obviously,but with the decrease of water binder ratio,this phenomenon is improved.Finally,after determining the optimal carbonation time,the effects of carbonated fly ash with different contents on the mechanical properties,impermeability and chloride ion permeability of cement mortar were studied.It was found that the early strength of the specimens was significantly improved under carbonation curing,and the 7d compressive strength of the specimens was significantly higher than other working conditions under the synergistic effect of carbonation curing and carbonated fly ash.Under carbonation curing,the capillary water absorption and electric flux of the specimens are significantly reduced,which improves the durability of cement mortar,and the improvement effect of carbonated fly ash cement mortar is more obvious.The carbon absorption of cement mortar after carbonation curing can reach 6.15%,but with the addition of fly ash,the carbon absorption of cement mortar decreases.