Study On The Influence Discipline Of Electrochemical Chloride Extraction Treatment On Performances Of Concrete

The reinforcement corrosion is one of the main factors causing the reduction of the reinforced concrete structure durability and failure of structure. It causes huge economic loss directly and indirectly. There are many reasons accounting for the reinforced concrete corrosion. From the statistics of the present project destruction, various chlorine ion's invasion causes the steel corrosion. the electrochemistry method can discharge the chloride ion without destroying the original concrete protective layer and realize the non-destroy, low cost and fast repair for the concrete structure destroyed by the chloride ion corrosion. This technology has been used in the advanced countries.The experiments discussed in this thesis uses the self-developed electrochemistry chlorine extraction machine and carries out the electrochemistry chloride extraction of concrete containing different water-cement ratio (0.45,0.38,0.32 )and mineral admixtures. The mineral admixtures are added by 5% or 10% silica fume, 10% or 20%fly ash, 20% or 40% slag respectively. Meanwhile, the effects of chloride ion content chloride ion introduction ways and electrochemistry parameters on efficiency of electrochemistry chloride extraction and the distribution of the residual ions, were investigated. The electrochemistry parameters include different voltage (20 V , 40 V , 60 V), and different electrolyte solution (0.1mol/L Na3BO3 solution, the saturated Ca(OH)2 solution, tap water). At the same time, it follows reinforcement spontaneous potential, the reinforcement corrosion current and the concrete resistance change by using the half-element potential method, the current step method and the linear polarization method; At last, it carries out the observation on morphology of the cement hydration product and pore structure before and after the chloride extraction by the SEM and mercury porosimeter. It tries to reveal the influence of electrochemistry chloride extraction on the reinforced concrete structure from the microscopic view.The experimental results show that the chloride extraction increases with the water-cement ratio increasing, compactness of concrete is increased and the chloride extraction is influenced owing to the addition of mineral admixture. For the concrete with the same chloride introduction way, the chloride ion concentration is higher, the electric flux and the amount of the chloride extraction are more. The voltage exerted is higher, the chloride exaction of concrete in the initial period is higher, while chloride exaction at age of 14days is little. The chloride extraction efficiency of different electrolyte solution decrease successively as follows: Na3BO3 solution with 0.1mol/L > saturated Ca(OH)2 solution > tap water.The external electric field causes positive and negative ion to migrate and aggregate clearly in the concrete. After electrochemistry chloride extraction, the amount of chloride ion in the outer layer of concrete specimen is 2~3.5 times of that of the nearby the steel bar, the amount of K+ and Na+ nearby the steel bar can be 25 times and 35 times of that in the outer layer respectively. This kind of disparity can increase through the voltage enhancement and the electrolyte electrolysis ability's enhancement.Before the chloride exaction, the bigger the water-cement ratio is , the lower the spontaneous potential is. The reinforcement corrosion current is bigger and the concrete resistance is lower. The adding mineral amixture makes the reinforcement spontaneous potential positive. The fly ash content is more and the reinforcement corrosion current is higher, but the concrete resistance has no obvious change. The additon of the silica fume or slag makes the reinforcement corrosion current lower and the concrete resistance higher. The more is the immersion ion or the more dense is the salt solution, the spontaneous potential is more negative. The reinforcement corrosion current is lower and the concrete resistance is higher. The longer is the curing time, the value of the spontaneous potential is higher, the reinforcement corrosion current is smaller and the concrete resistance is bigger.In the process of the chloride extraction, the spontaneous potential of all the samples transfer negatively to the -1V obviously, and then the spontaneous potential remains constant. With electrochemistry chloride extraction time extension, the reinforcement corrosion current of all the samples increase constantly; the reinforcement corrosion current remains constant when electrifying 14days.The electrochemistry chlorine extraction causes Na+ and K+ ion to gather nearby the steel bar, makes the hydration product nearby the concrete soft and the water content in the interface of reinforced concrete to increase. It makes the lubricity between the steel bar and the concrete surface increase. The ion migration causes the inner layer concrete hydration product decomposition and the change. The comprehensive result of this change makes the adhesion strength between the plain steel bar and the concretes reduce up to 60%; Meanwhile, the longer is the electrochemistry chlorine extraction, the higher is the electrolyte electrolysis ability , and the bigger is the adhesion strenth loss ratio between the steel bar and the concretes.The electrochemistry chloride extraction makes the morphology and the pore structure of the cement hydration product in different depth change a lot. The porosity and micro pore content of the region nearby the steel concrete after the electrochemistry chloride extraction increase, and part of hydration product is decomposed. The hydration product in the outer layer of concrete is network shape, pore size is refined and the structure is compacted. Meanwhile, There are some acicular and the granular crystals in the hole, which enhance impermeability to resist outside medium seepage and durability of the concrete. Keyword: performances of concrete, electrochemistry chloride extraction, ion...