Study On Reinforcement Corrosion Performance In Cecycled Aggregate Concrete With Original Concrete Eroded By Chloride Ion

There are a large number of buildings in the coastal and de-icing environment in China.In this environment,the original concrete is eroded by different degrees of chloride ion,so that the chloride content of the recycled aggregate often exceeds the standard(the limit is 0.06%),leading to the limitation of its recycling.In this thesis,using nano-SiO2 solution strengthening and CO2 strengthening to treat recycled aggregates eroded by chloride ion,in order to reduce the content of chlorine ion of recycled aggregate and enhance the performance of recycled aggregates,at the same time mineral admixture was blended to the mix proportion design of recycled concrete,and the optimizing mix proportion of corrosion-resistant recycled concrete was obtained.It lays the foundation for the regeneration of original concrete that is attacked by chloride ions.A total of 33 sets of recycled concrete mix ratios were designed to produce small beams with a size of 100mm ×100mm ×400mm.After standard curing 28d,and the electric power accelerates the corrosion 28d.The corrosion current density and polarization resistance of each corrosion age were tested by the PARSTAT4000 electrochemical workstation,and the effect of each variable on the corrosion performance of the steel bar was studied.This paper mainly carried out the following research:1.Ordinary recycled aggregate and the recycled aggregate with chloride content of 0.124%,0.283%,0.385%and 0.581%were prepared respectively.The nano-SiO2 solution strengthening program with different solution concentrations and different strengthening times and the CO2 strengthening program with different pressures of CO2 and different strengthening times were used to treat the recycled aggregates.The results showed that both of the two methods can reduce the chloride ion content,water absorption rate and crushing index of recycled coarse aggregate.When the concentration of nano-SiO2 solution was 4%and the strengthening time was 48h,the chloride content decreased from 0.581%to 0.237%,and the enhancement effect was the best.The pressure of CO2 strengthening was 0.1MPa,while the concentration of chlorine ion decreased from 0.581%to 0.382%when the strengthening time was 24h,5 and the enhancement effect was the best.Moreover,the enhanced effect of nano-SiO2 solution is better than that of CO2.2.According to the different chloride ion content of aggregate and different aggregate reinforcement methods,15 sets of recycled concrete mix proportions without mineral admixture were designed to test the corrosion performance of the steel bars.It was found that that chlorine ion content of the regenerated aggregate was in a linear relation with the corrosion rate of the rebar,and the corrosion rate of the rebar was decreased with the increase of chloride ion content of the recycled aggregate after the corrosion of 3d.The reinforcement corrosion performance of recycled concrete was promoted by using nano-SiO2 solution strengthening and CO2 strengthening.However,only through the enhancement of recycled aggregates,even if the recycled aggregate has the lowest chloride ion content(0.124%),the reinforcement corrosion resistance of recycled concrete is still inferior to ordinary recycled concrete.3.On the basis of the above-mentioned aggregate strengthening,after mixing different proportion of mineral admixtures,18 groups of recycled concrete mixture ratio were designed,a set of test set total replacement ratio of fly ash and slag is 40%,the proportion of the mixture was 3:7,5:5 and 7:3;the other group set the fly ash content of 30%,compounded by 3%,5%and 8%silica fume.It can be found that the reinforcement corrosion rate is increased with the increase of the proportion of fly ash and slag,and the optimal ratio is 5:5.The reinforcement corrosion rate decreases with the increase of silica fume content,and the optimal compounding ratio is based on 30%of fly ash content,and 8%of silica fume is blended.The reinforcement corrosion performance of the recycled concrete with the optimum ratio of fly ash and silica fume are better than that of mixed fly ash and slag.Compared with ordinary recycled concrete,no matter whether the aggregate is strengthened or not,it is only necessary to add the mineral admixture mentioned above.Even if the content of chloride ions in recycled aggregate is the highest(0.581%),the reinforcement corrosion performance of the recycled concrete is superior to the ordinary recycled concrete.4.Based on the existing steel corrosion model,this paper statistically analyzes the corrosion current density of 33 groups of recycled concrete,and establishes the prediction model of steel corrosion with the content of chloride ion,the proportion of different mineral admixtures and different corrosion ages.