The Effect Of Carbon Dioxide Curing On Properties Of Cement-based Materials With Fly Ash

At present,countries pay more and more attention on energy conservation and emissions reduction.The reduction of carbon emission becomes more and more important.Recently,researches on fixing carbon dioxide gas through the concrete manufacture have been hot spots.Based on the previous work on the carbonation curing of precast cement-base materials,the CO₂ curing technology of ordinary concrete mixed with fly ash was studied.Proper CO₂ curing process parameters of fly-ash concrete has been found and the concrete carbonation degree has been analyzed.First,carbonate titration method was developed for the determination of carbonation degree and carbonation depth of cement paste with fly ash under CO₂ curing degree and then mechanical behavior of concrete mixed with different content fly ash were investigated.Incorporated reaction dynamics of concrete under CO₂ curing with the microstructure change before and after CO₂ curing,the influence of CO₂ curing on fly ash concrete has been found.This study found that fly ash could improve the CO₂ curing degree of the cement based material with absorbing more carbon dioxide.CO₂ curing mainly affected specimen surface that fly ash could increase the depth and degree of carbonation.The specimen with 40% fly ash acquired the maximum carbonation degree and effect of applying ground granulated blast furnace slag and fly ash to cement paste has been studied.The influence of water-to-cement ratio was studied,the higher the water-to-cement ratio was,the bigger the carbonation degree of the specimens was.The specimen with water–to-cement ratio of 0.45 had the biggest carbonation degree and the carbonization depth increased with the increase of water-to-cement ratio.After the dry pre-curing test,specimen had been cured by CO₂ and the strength of the specimen could meet or exceed the strength of the control specimen.The strength of the wet-cured specimen was not changed after CO₂ curing.High concentration of carbon dioxide could improve the degree of carbonization of the specimen,effectively improving the mechanical properties of the specimen.After CO₂ curing,concrete mixed with 20% fly ash showed higher 3d,7d and 56 d strength than the fly ash-free specimen.For the specimens incorporated of fly ash,when the degree of carbonation curing of the specimen increased,the strength of concrete increased.Combined with XRD,SEM and Mercury intrusion porosimetry analysis,the harmful pores in the specimen decreased after carbon dioxide curing and the structure became more compact,so the mechanical properties of the specimen could be improved.The content of early harmful pores was increased by mixing with fly ash,the increase in large pores was conducive to the proliferation of carbon dioxide,improving the degree of carbon dioxide conservation.The harmful pores in the specimens declined after CO₂ curing and fly ash would promote the hydration degree of cement clinker.Through the dry pre-curing,the degree of CO₂ curing could increase and adopting fly ash content of 10% and 40% in the specimens could get the biggest carbonization degree.The initial strength can be improved by dry pre-curing and increasing the concentration of CO₂.However,the later strength of the specimens mixed with fly ash was mainly from the secondary reaction of fly ash.The strength of the specimen was positively correlated with the degree of CO₂ curing,and the higher the degree of carbon dioxide curing,the greater the strength increased.Thus,when adopting the humidity of 60% of the pre-curing and concentration of 90% of the CO₂ conservation would increase the degree of CO₂ curing and increase the strength of fly ash concrete.