A Study of the Changes in Concrete Properties Using Different Electrochemical methods

• Main Authors: Chang, Cheng-Chin, 張正勤
• Other Authors: Chang, Jiang Jhy
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/3xv2wd

博士 === 國立臺灣海洋大學 === 河海工程學系 === 104 === In this dissertation, the non-destructive electrochemical method was developed to protect or repair reinforced concrete and to build an integrated database of using electrochemical method in protecting or repairing reinforced concrete was the major goal. There are four categories in this dissertation and they are briefly described in the followings. 1.The influence of cathodic current on the alkali-silica aggregate reaction. The results showed that the crack initiation time increased as the initial alkali content increased, and decreased as the current density and water cement ratio increased. In addition, the accelerated alkali-silica aggregate reaction was observed at the rebar-concrete interface from the micro-hardness test and the accumulated sodium and potassium ion contents. As the influencing parameter , which is defined as the product of the cathodic current density and polarization time, increased, the yield strength, ultimate strength and elongation percentage degraded and the degradation effect was most apparent for the elongation percentage. It indicated that the cathodic current resulted in embrittlement of rebar. The results of this part provide engineer a warning while applying cathodic protection. 2.Electrochemical rehabilitation for cement based material suffered from alkali-silica aggregate reaction Results showed that the electrochemical habitation for cement based material suffered from alkali-silica aggregate reaction using 2N LiOH solution as electrolyte performed better than that using 1N LiOH in length change and compressive strength. In addition, when the second-time accelerated alkali-silica aggregated reaction was performed on repaired specimens the degradation on compressive strength for that repaired using 2N LiOH solution was less. However, the electrochemical deposition method had better effect on compressive strength restoration than the electrochemical migration of lithium ions no matter for cracked specimens or uncracked specimens. For cracked specimens, electrochemical deposition method resulted in calthium rich deposits on crack surface which increased the capability of preventing water and chloride penetration, and prevented the corrosion and carbonation. 3. The chloride removal efficiency of the electrochemical chloride extraction on reinforced concrete members with ribs Due to the existence of reinforcement cage, the chloride removal efficiency for chloride ions enclosed by the reinforcement cage was low, which was not observed for single rebar specimen. The chloride removal only was effective for concrete between titanium mesh (anode) and reinforcement (cathode), and for concrete not in this region the chloride removal efficiency became low. However, adding additional cathodic cell or interchanging the electrolysis cells can increase the chloride removal efficiency. Calcium carbonate was observed on anodic side except that using 0.1 N NaOH solution in the anodic cell as electrolyte. This result indicated that leaching of calcium ions happened during the process and if the leaching of calcium ions was severe it might resulted in enlargement in pore size and decrement in compressive strength. 4.The electrochemical chloride extraction method using auxiliary electrodes Two new electrochemical chloride extraction methods using auxiliary electrodes were developed. Results revealed that from mechanical behavior, physical property, chemical property and electrochemical property these two new methods showed no negative effect. The parallel arrangement of auxiliary electrodes (method B) performed better than the radial arrangement of auxiliary electrodes (method A). After 8-w desalination, more than 73% chloride ions were removed for both methods which meant the electrochemical chloride extraction method using auxiliary electrodes resolved the problem of worse removal efficiency for concrete with rebar cage and increased the chloride removal efficiency.