Study On Resistance Performance Of Recycled Concrete Subjected To Chloride Ion Erosion On Original Concrete To Chloride Ion Corrosion

The original concrete in the coastal areas of China has been eroded by chloride ion in different degrees,resulting in chloride ion content to exceed national regulatory standards in recycled aggregates after crushing.The research group has studied samples of original concrete at different distances from coastline in coastal areas such as Pingtan and Changle in Fujian province.The test results show that the chloride ion content of recycled coarse aggregates obtained by crushing original concrete,which was Om,30m,100m,and 200m from the coastline,was 12 times,4 times,2 times,and 1 times more than the specification limit(0.06%)respectively.It can be seen that a large amount of waste concrete offshore or under the sea is excluded from the scope of renewable use due to the erosion of chloride ion.In this paper,the corrosion resistance performance of recycled concrete against chloride ion is improved through two methods of strengthening the recycled aggregate and adding mineral admixtures,so that the waste concrete in the coastal area can be recycled.The main research contents and results of this paper are as follows:1.Special CO2 high-pressure reactor is used to perform CO2 strengthening treatment on recycled aggregate with excessive chloride ion content,considering the different CO2 strengthening pressure and strengthening time,a total of 36 groups of experiments were designed to investigate the optimal CO2 strengthening method.Nano-SiO2 solution was used to soak the recycled aggregates with excessive chloride ion content,considering the different solution concentrations and soaking time,a total of 28 groups of experiments were designed to investigate the optimal strengthening method of nano-SiO2 solution treatment.The experimental results show that both of the two strengthening methods can reduce the free chloride ion content of recycled aggregates,reduce the water absorption and crushing indexes and increase the apparent density of recycled aggregates.When the CO2 strengthening pressure is 0.1MPa and the strengthening time is 24h,the effect is optimal.When the solution concentration is 4%and the soaking time is 48 hours,the effect is optimal.2.Setting the different chloride ion contents of the recycled aggregate and different strengthening methods as variables,without mixing mineral admixtures,15 sets of mix proportions were designed to produce 45 recycled concrete specimens of size ?100mm×50mm.The electric flux of each sample was measured by the ASTM C1202 electric flux method,and the influence of different factors on the resistance to chloride ion erosion of recycled concrete made of original concrete eroded by chloride ions was studied.Experiments show that both the optimal strengthening methods of nano-SiO2 solution and CO2 can effectively reduce the electric flux of this kind of recycled concrete and that the former is more effective.After the recycled aggregate with chloride content less than 0.124%was treated by the optimal strengthening method,the prepared concrete had stronger resistance to chloride ion erosion than ordinary recycled concrete.3.Based on the use of the optimal strengthening method,different kinds and amounts of mineral admixtures were mixed in the recycled concrete,and the chloride ion content of the recycled aggregate was 0.581%.18 sets of mix proportions were designed to produce 54 recycled concrete specimens of size ?100mm×50mm.The same test method was used to study the influence of different variables on the resistance to corrosion of chloride ions of such recycled concrete.The test results show that the recycled concrete resistance to chloride ion erosion is stronger than ordinary recycled concrete when the combined total of fly ash and slag is 40%and the ratio is 3:7,5:5,7:3,or 3%,5%,8%of silica fume are added respectively on the basis of 30%addition of fly ash.The effect is best when the proportion of fly ash and slag is 5:5,or the fly ash content is 30%and the mixed silica fume content is 8%.The superimposed effect of the optimal strengthening treatment of recycled aggregates and the addition of mineral admixtures can further reduce the electric flux of recycled concrete to less than 1000C.The permeability evaluation grade is "very low" and it is a high impermeability recycled concrete.4.Based on the above 33 sets of mix proportion,99 recycled concrete specimens of size?100mmx50mm were produced and the diffusion coefficient of each specimen was measured by NEL method.Based on this,according to the existing chloride ion diffusion model,a chlorine ion diffusion model for such recycled concrete considering the different chloride ion contents of recycled aggregates and different mineral admixtures was established.