Study On Electrochemical Chloride Extraction And Post Performance Of Reinforced Concrete

Corrosion of steel bar in concrete due to chloride ions attacking is one of the major reason leading to the degradation of reinforced concrete structures (RC) throughout the world. In order to extend the service life of existing RC structures contaminated by chloride ions, a non-destructive repair technique electrochemical chloride extraction (ECE) of reinforced concrete was developed, which involving mounting a temporary anode on the surface of the concrete and applying a direct current between this anode and the embedded steel bar to drive chloride ions away from steel bar and out of the concrete. Based on experiment of ECE, the efficiency of electrochemical chloride extraction and the side-effect may occurred in the process of electrochemical chloride extraction were studied. The details as follows:1. The effect of initial content of chloride, current density and electric quantity on efficiency of ECE was studied by determining the content of chloride ion in concrete. It is indicated that free chloride ion could be extracted from concrete by electrochemical chloride extraction.The less the initial content of chloride ion is, the higher the efficiency of electrochemical chloride extraction is. But for the same conditions of current density and electric quantity, the absolute amount of chloride ion extracted from concrete increased with the increasing of initial content of chloride ion. Current density adopted in ECE treatment has a little effect on the efficiency of ECE. Electric quantity adopted in ECE has an important effect on the efficiency, the more the electric quantity is, the higher the efficiency of electrochemical chloride extraction is. However, the increment of the efficiency is not clear when the electric quantity exceed 1500A·h/m2. The potential of steel bar was measured before and after ECE. It was found that the potential increased to more positive after ECE, which means the corrosion probability of steel bar decreased. And XRD results shows the content of Ca (OH)2 increased after ECE which contributes to the repassivation of steel bar.2. Compressive strength and permeability of specimens experienced ECE with different current density were measured. It is concluded that electrochemical chloride extraction has a little effect on the macro-compress strength of concrete, and improves the impermeability of concrete.3. The bond behaviour between steel bar and concrete after ECE treatment was studies using beam specimens. It is indicated that the bond behaviour between steel bar and concrete was deteriorated after electrochemical chloride extraction, the more the current and the electric quantity of ECE are, the more the loss of bond strength is. The effect of initial content of chloride ion on the bond strength can be neglected.4. By determining the content of chloride ion in freeze-thawed concrete after ECE treatment, it is shown that for the freeze-thawed reinforced concrete contaminated by chloride, the number of freeze-thaw cycle has a little effect on the efficiency of electrochemical chloride extraction, and the effect of current density and electric quantity on the efficiency is similar with that of unfreeze-thawed reinforced concrete.5. The bond behaviour between steel bar and freeze-thawed concrete after ECE treatment was studies using beam specimens. It can be concluded that the combined action of freeze-thaw cycles and electrochemical chloride extraction treatment results in the degradation of bond between steel bar and concrete, and the degree of bond degradation is not a simple superposition of the two action effect. With the increase of current density, electric quantity of electrochemical chloride extraction and the increase of freeze-thaw cycles, the bond strength obviously decreases. The effect of electrochemical chloride extraction on the bond strength of unfreeze-thawed specimens is greater than that of freeze-thawed specimens.6. Based on the test results of 7 ECE treated reinforced concrete columns under low reversed cyclic loading, the effects of ECE on seismic behavior of reinforced concrete column is analyzed. Owing to the degradation of bond between steel bar and concrete induced in the process of electrochemical chloride extraction treatment, the seismic behavior of reinforced concrete circular column contaminated by chloride was deteriorated, but the degree of deterioration is lower than that of bond strength of beam specimens which experienced electrochemical chloride extraction treatment with the same current density and electric quantity. With the increasing of current density and electric quantity, the bearing capacity, ductility and energy dissipation capacity of column decreased and the deterioration rate of stiffness increased.