Research On The Electrochemical Approach To Accelerate The Dissolution Of Concrete

The electrochemical approach to accelerate the dissolution of cement based materials is a new technology that emerges internationally in recent years. It has been applied to researches to accelerate the dissolution of cement paste and mortar, and results in significant conclusions. Although the approach is feasible in the cases of cement paste and mortar, there are few reports about researches on concrete, especially fiber concrete. Researches on the dissolution of concrete concentrate on that of face concrete and roller compacted concrete. The field of electrochemical approach to accelerate dissolution of concrete still remains uninvestigated. In order to study its feasibility, the thesis develops the experimental researches from following aspects considering the shortages in present study:1. A set of testers of electrochemical approach to accelerate dissolution of concrete are designed and leads up in trial runs to the fact that: the electrified liquor in which specimen is immerged produces abundant bubbles, and its pH value changes distinctively. The change appears suddenly at the beginning of electrification, and then levels off. The current first increases to the climax, and gradually decreases. The higher the voltage is, the more time it takes to reach the climax. The dissolution amount of Ca²⁺ is large at the beginning, and shows a tendency of decreasing then. The diversifications of pH value of the liquor, current, and dissolution amount of Ca²⁺ cast mutual influences on each other. CaCO₃ turns out in the liquor. The conclusion is that the testers are available for electrochemical approach to accelerate dissolution of concrete.2. Comparing the dissolution amount of Ca²⁺, influences on the dissolution rate cased by the distance of the electrodes, voltage, environmental temperature, pH value of the liquor, and other factors are carefully studied to the following conclusions: the distance of the electrodes hardly impacts the dissolution rate. The higher the voltage is, the more rapid the dissolution is. Higher environmental temperature results in more rapid dissolution. PH value of the liquor near cathode influences the rate greatly.3. Electrochemically accelerating the dissolution of cement paste specimen, normal-strength concrete specimen, concrete specimen with silica fumes, and concrete specimen with fibers separately, properties of the dissolved and non-dissolved concretes are compared after a long period of dissolution considering the indicators such as dissolution amount of Ca²⁺ (count by CaO), water absorption rate of dry saturated surface, rate of ultrasonic wave, compressive strength, tensile splitting strength, dissolution depth, and frost resistance, and so on. Conclusions are drawn that dissolved electrochemically, the properties and indicators are changed more or less. Strength and durability of the concrete are reduced in different degrees. Concrete mix proportion influences the effect of electrochemical dissolution greatly; the larger the w/c is, the greater the unfavorable impact is. Concrete specimen with silica fumes suffers from less unfavorable impacts because of less amount of Ca(OH)2 in it and compact structure; Concrete specimen with steel fibers is seriously damaged for dissolution of large amount of Ca(OH)₂ and rust-eaten; In concrete specimen with polypropylene fibers, dissolution amount of Ca(OH)₂ is similar to normal-strength concrete, but performance of fibers are reduced because of dissolution.4. Through analyses of dissolved and non-dissolved specimens by means of X-ray diffraction, scanning electron microscopy, energy spectrum analysis, microcellular structure testing, microhardness testing and etc., conclusions are draw that electrochemical acceleration of the dissolution reduces greatly, even extinguishes the amount of Ca(OH)₂. The amount of other hydrates such as calcium silicate, and etc., are hydrolyzed. As a result, the amount of Ca²⁺ and the density are reduced. Meanwhile, as the porosity is increased, the pore structure is changed with more big ones and relatively less small ones. On the whole, the rigidity of the concrete is reduced, and the structure is gradually damaged. Finally, mechanism of the electrochemical acceleration of the dissolution of concrete are studied from macro and micro tests comprehensively,The thesis focuses on the electrochemical acceleration of the dissolution of concrete, which provides later researches in the field with certain reference value.