Study On Anti-Carbonization Of Recycled Concrete

With the application of recycled concrete more and more attention has been paid to the construction waste used in the production of concrete products not only the possibility of material supply but also the production scale and efficiency guarantee.However,under the action of CO₂ and SO₂,the concrete structure will be carbonized,and the concrete carbonation reaction will reduce the Ca?OH?₂ concentration and pH in the pore water,resulting in the reinforcement desensitization and corrosion.This is the main negative effect of concrete carbonization on concrete structure.The carbonation of concrete will be an important research topic in the field of concrete materials.Therefore,by setting three factors and three levels of orthogonal test,the influence of"water-cement ratio,ratio of recycled coarse aggregate substitution,fly ash content"on the carbonation resistance of recycled concrete was studied,and the compressive strength test was set up.The relationship between compressive strength and carbonation resistance of concrete is studied.The changes of recycled concrete before and after carbonization are analyzed by SEM.The carbonation resistance of recycled concrete is analyzed from the microscopic point of view.The experimental results show that:?1?Under the influence of single factor,the carbonation depth of recycled concrete increases with the increase of water-cement ratio,and the carbonation depth of recycled concrete increases with the increase of the replacement ratio of recycled coarse aggregate.However,the carbonation depth of recycled coarse aggregate is very close to that of 25%and 50%,and the carbonation depth of recycled concrete increases with the increase of fly ash content.The carbonation resistance of recycled concrete is the best when the content is 10.The influence of three factors on the carbonation depth of recycled concrete in 28 days is in the order of water-cement ratio>fly ash content>replacement rate of recycled coarse aggregate.?2?Under the influence of a single factor,the compressive strength of recycled concrete and the carbonation depth of recycled concrete are obvious,and the greater the compressive strength is,the smaller the carbonation depth is,that is,with the increase of water-cement ratio,the compressive strength of recycled concrete decreases gradually.The compressive strength and carbonation depth of recycled concrete decrease gradually with the increase of the replacement ratio of recycled coarse aggregate,and with the increase of fly ash content,the compressive strength of recycled concrete decreases gradually,and the carbonation depth increases with the increase of the content of fly ash.The compressive strength of recycled concrete decreases gradually and the carbonation depth increases gradually.?3?Comparing the above 9 kinds of recycled concrete,it is concluded that the recycled concrete with water cement ratio of 0.5,recycled coarse aggregate replacement ratio of 25%and fly ash content of 10%has the best carbonization resistance.?4?The microscopic morpHology of recycled concrete before and after carbonization was compared directly by electron microscope test.It was found that the water-cement ratio was the main factor affecting the microvoids in recycled concrete,and with the increase of water-cement ratio,the microvoids in recycled concrete increased.After carbonization,a large number of microvoids are coarsened,which will produce microcracks seriously.It is considered that the carbonation resistance of recycled concrete with the ratio of water to cement is 0.5,the ratio of recycled coarse aggregate is 25,and the content of fly ash is 10%.The C-S-H gel is arranged neatly before carbonization.The tiny C-S-H gel encapsulated Ca?OH?₂ tightly,and a large number of microvoids formed between the gel and the crystal were filled to form a more uniform and dense continuum.After carbonation,the C-S-H gel became irregular.only a small amount of granular CaCO₃ appeared on the surface of Ca?OH?₂.