| The penetration of chloride ions and the induction of corrosion of steel bars in concrete is a critical cause for the degradation against durability performance of reinforced concrete structures under marine environment.Electrochemical chloride extraction is a protection method which can effectively remove chloride ions in concrete and remain the performance of steel bars.In this paper,polymer modified conductive repair mortar is firstly developed,taking into account the difficulty of laying,rusting,and high cost of traditional stainless steel mesh and titanium mesh anode materials.Then study the effectiveness of electrochemical chlorine extraction and the quantitative influence of electrochemical parameters,concrete type,and steel bar layout on the efficiency of electrochemical dechlorination by using the polymer modified conductive repair mortar as the anode material for electrochemical chlorine extraction,and the effective measures to improve the efficiency of electrochemical chlorine extraction are put forward.The Constant potential accelerated corrosion and electrochemical chloride extraction tests are carried out using reinforced concrete specimens.The effectiveness of electrochemical chlorine extraction and its effect on reinforcement properties were analyzed according to monitor the stress/strain and electromagnetic field changes in the process of steel corrosion and performance recovery.The main conclusions are as follows:(1)Sulphoaluminate cement is used as the main cementing material,silica fume and mineral powder are used as auxiliary cementing materials,carbon fiber is the conductive phase,meanwhile,0-3% renewable modified latex powder(EVA)is added to prepare the polymer modified conductive repair mortar which aims to study its workability,compressive/flexural strength,bonding strength,permeability resistance and volume stability.The test results show that the setting time of EVA modified mortar is prolonged,fluidity is increased,and overall workability is improved;the addition of EVA improves the flexural strength of the repair mortar and also reduces the compressive strength,however,the toughness and bonding strength of the mortar are improved.The addition of EVA improves the resistance capacity to chloride ions penetration of the repair mortar,and also reduces the drying shrinkage and water absorption of the mortar.The recommended mixing proporation of high-performance polymer modified repair mortar is cementing material: sand:water=1:1.5:0.35,the content of polymer redispersible latex powder is 2%,the content of carbon fiber is 0.6%,respectively.(2)The electrochemical chloride extraction experiment on reinforced concrete with chloride ions,different steel bar layout and different strength levels was carried out,which contains using polymer modified conductive repair mortar as anode and setting different thicknesses.The results show that the addition of 0.6% carbon fiber to the polymer modified repair mortar reduces the resistivity of the mortar to about120 Ω·cm,which can be applied as an electrochemical chloride extraction anode.Compared with the stainless steel mesh anode,the conductive repair mortar anode has a slight lower chloride extraction efficiency,which can be used as a later cathodic protection anode and ordinary protective coating that can be recycled.The thinner of the conductive repair mortar anode,the higher the electrochemical chlorine extraction efficiency.Yet there is a phenomenon of chloride ion enrichment at the interface between the repair mortar anode and the concrete.The higher the desalination current density and the longer the electrification time,the higher the electrochemical dechlorination efficiency.The higher the strength and the denser the concrete,the lower the desalination efficiency.The steel cage in the concrete has the same electric potential after electrification,and the chlorine in the steel cage ions are difficult to remove by electrochemical chloride extraction efficiently.(3)To study the effects on electrochemical chlorine extraction efficiency and chloride ion enrichment in anode-concrete surface,such as intermittent pulse current,conductive repair mortar mesh laying,double anode layout.The test results show that compared with continuous current,intermittent pulse current can effectively improve the efficiency of electrochemical chlorine extraction.Among the parameters,the desalination efficiency of continuous energization for 14 days can be achieved with 3days power on and 3 days power off respectively..By arranging the conductive repair mortar anode into a grid,the contact area of the electrolyte solution is more conducive to the discharge of chloride ions and reduces the concentration of chloride ions at the interface.The use of conductive repair mortar and stainless steel mesh double anode arrangement which can prevent the mortar from cracking,and also shorten the migration distance of chloride ions,and reduce the chloride ion at the interface enrichment that can improve the efficiency of desalination.(4)The corrosion of reinforced concrete is accelerated by infiltration of chloride chlorides and constant potential,and electrochemically chlorine extraction is performed using conductive repair mortar anodes,and also with strain gauges attached to the inner wall,electromagnetic sensors,etc,which are used to monitor the corrosion of steel bars and the strain in the process of dechlorination.The results have shown that the corrosion expansion stress of steel bars is applied to the inner wall of the steel bars,and the strain can be monitored by internal strain gauges and the stress can be calculated.The magnetic permeability variation caused by the corrosion products of the steel bars can be monitored by the changes of the Hall voltage signal of the embedded electromagnetic sensors.The cracking of the concrete makes the extravasated solution reach the surface of the steel bar directly and the corrosion current increases suddenly.It can effectively remove chloride ions in concrete and the performance of steel bars can be restored by using polymer modified conductive repair mortar as anode to electrochemical chlorine extraction of accelerate corrosion reinforced concrete. |
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