Effect Of Carbonation On Chloride Binding And Rebar Corrosion Of Concrete Made With Marine Sand

Chloride in marine sand can cause large area corrosion of rebar in concrete.Even if the initial free chloride ions content introduced by marine sand is lower than the critical threshold,considering the effect of carbonization on the release and internal migration of solidified chloride ions,marine sand concrete structures may also be subject to the risk of durability damage beyond design expectations.The chloride ions curing and corrosion behavior of rebar in marine sand concrete were studied in this research.The main conclusions are as follows:(1)The carbonation re-releases the combined chloride ions into free chloride ions.the content of chloride ion in the carbonization zone of the carbonization zone is significantly higher than that in the non-carbonization zone,and carbonization drives chlorine ions migration.(2)Chloride ions have a certain influence on the anti-carbonation ability of concrete.The introduction of a certain amount of chloride ions in the marine sand will help improve the anti-carbonization ability of the concrete,which is related to the fact that chloride ions can promote cement hydration degree.(3)The model of chloride ions transport inside the concrete under carbonization was deduced.This model can be used to characterize the distribution law of chloride ions content increasing first and then decreasing along the depth of carbonation,and the time-dependent change of chloride ions concentration distribution curve.(4)The thickness of the protective layer has a certain influence on the corrosion potential of the rebar.Before the carbonization,the change of the corrosion potential of the rebar is not obvious.After the carbonization,the corrosion potential of the rebar with a smaller protective layer thickness affected by the carbonization zone is significantly reduced.While the thickness of the protective layer is larger,the rebar potential is essentially unaffected.The surface treatment method of rebar also has a certain influence on corrosion potential and corrosion current density of rebar.For Corrosion potential,the pre-rust rebar are the most positive,followed by rebar of original condition,and the potential of chemical treated rebar is the most negative;For corrosion current density,the chemical treated rebar has the smallest value,followed by the original rebar,and the Pre-rust rebar were the largest.(5)Early carbonization has a certain inhibitory effect on the corrosion process of rebar.Carbonization makes the concrete of the protective layer more dense,with increasing the resistivity of the concrete electrolyte,and reducing the corrosion rate of the rebar.(6)The actual engineering investigation shows that there exists a chloride concentration peak after carbonization.Chloride ions can be accumulated on half carbonized zone,which causes significantly increase of local free chlorine ions.Due to the dual effects of peak chloride content and carbonization,the degree of steel corrosion in concrete is very severe.(7)Accelerated carbonation tests and engineering investigations have proved that the concrete structure with marine sand must consider the synergistic effect of carbonization and chloride ions.The limit of chloride ions in marine sand concrete structures and the reasonable selection of existing marine sand concrete control measures should be carefully determined.