Durability Of Reactive Powder Concrete Under The Action Of Chloride Salt Freeze-thaw Cycling And Erosion

Durability failure of concrete structure caused by the coupling of multi-factor action is getting worse.Reactive powder concrete is a kind of cement-based composite materials with high mechanical properties and excellent durability,which is suitable for using as the body or protective materials of concrete structures in harsh environment.The durability of reactive powder concrete under coupling action of freeze-thaw cycling and chloride ion erosion was studied in this paper.The single factor action of chloride ion erosion test,coupling action of freeze-thaw cycling and chloride ion erosion test,capillary absorption test,chloride ion content test,and rehydrated test were carried out respectively.The performance indicators of reactive powder concrete under coupling action were measured,and the life prediction of reactive powder concrete was carried out.Finally,the deterioration mechanism of reactive powder concrete was analyzed.The physical and mechanical properties of reactive powder concrete under the action of chloride ion erosion as well as the coupling action was studied first in this paper.The mass loss rate increased slightly increase with the increase of cycling times,and relative dynamic elastic modulus was almost constant during the cycling.The variation of the compressive strength could be divided into three stages,namely,the initial rapid decline stage,stable stage and accelerated decline stage.The compressive strength decreased with the increase of natural soaking time,and it reduced by 14.5%after 720d soaking.It may be caused by the rehydration.The use of mass loss rate to evaluate the durability of reactive powder concrete coupling was unscientific.And the relative dynamic elastic modulus should not be used as a separate evaluation index of reactive powder concrete.The calculation method of chloride ion diffusion coefficient was established based on test results of chloride ion content test.The chloride ion diffusion coefficient decreased first and then increased with the increase of cycling times.The service life prediction models of reactive powder concrete was establish considering the freeze-thaw damage,chloride erosion and coupling action,respectively.What's more,the diffusion of chloride ion under soaking and coupled cycling was modeled based on cellular automata model.The modeling could provide a reference for the modeling of erosion medium diffusion under complex environment.The capillary absorption characteristics of reactive powder concrete after natural soaking and coupled cycling were determined through capillary absorption test,and the influence solution concentration and steel fiber content were also took into consideration.Results show that the solution absorption of reactive powder concrete growth faster in the early and slower later,volume is proportional to t1/2,respectively,in 15-180 min and 180-540 min.The solution absorption of specimens after soaking 720 d was slightly larger compared with specimens without soaking.However,the solution absorption of specimens reduced significantly after coupled cycling.This may be also caused by rehydration.The influence of rehydration on the performance of reactive powder concrete was analyzed through rehydration experiment.It can be concluded that rehydration happened during the natural soaking and coupled cycling with flocculent,flake,needle bar,amorphous form and ettringite erosion product generated.The rehydration could lead damage to concrete structure with high density,but it also could repair the damage to a certain extent.A new rehydration model was proposed based on the hydration model of cement-based material,and the simulation values of proposed rehydration model were consistent with the experimental values.It could provide a reference for subsequent rehydration model researches.What's more,the influence of pore size and NaCl concentration on the freezing temperature was analyzed according to Gibbs-Thomson equation.The influence of NaCl concentration and temperature on volume expansion rate was also experimental studied.The reason of the performance changes of reactive powder concrete were elaborated according to these results.The higher density of its internal structure was the main reason for the excellent durability of reactive powder concrete under the coupled action of chloride salt freeze-thaw cycling and erosion.