Permeability And Prediction Of Free Chloride Ion In Recycled Aggregate Concrete With Fly Ash

Experimental work was carried out to investigate the free chloride ion penetration in recycled aggregate concrete with fly ash. By using the natural diffusion method, specimens with different fly ash content of 0%, 10%,20% and 30% were tested after corroding in fully saturation or wet-dry circulation for 30days, 60days, 90days and 120days respectively. And then specimen was drilled with diameter of 6mm to get the powder at the depth of 1 similar to 5mm, 6 similar to 10mm, 11 similar to 15mm and 16 similar to 20mm respectively, and then the powder was put in a bottle with distilled water. After 24 hours, this solution was filtered and neutralized by the diluted sulphuric acid; after ten drops of potassium chromate indicator was put into this solution, the silver nitrate solution was added to make it brick red, and the free chloride ion concentration was obtained by a formula. Then the impact of fly ash content and corroding time on free chloride ion (FCI) concentration (by mass) was discussed respectively; and the distributions of free chloride ion with the depth were also presented. And the mechanism of free chloride ion penetration was also put forward after comparison study between fully saturation and wet-dry circulation. Finally the improved grey model was applied to predict the FCI concentration in recycled aggregate concrete with different fly ash content after validation; and it is found that the model is feasible to predict with higher accuracy; and the prediction reveals that the effect of wet-dry circulation would decline with time and 20% was the best fly ash content for the durability of recycled aggregate concrete.