A Study of the Chloride Diffusion Coefficients of HPC (I)

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Project title

Code/計畫編號

NSC85-2211-E019-001

Translated Name/計畫中文名

高性能混凝土材料物化性質探討整合型研究---高性能混凝土氯離子擴散係數研究(I)

Project Coordinator/計畫主持人

Wei-Chung Yeih

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Harbor and River Engineering

Website

https://www.grb.gov.tw/search/planDetail?id=219346

Year

1996

Start date/計畫起

01-08-1995

Expected Completion/計畫迄

31-07-1996

Bugetid/研究經費

293千元

ResearchField/研究領域

土木水利工程

本研究旨在探討混凝土中加速氯離子擴散實驗的正確理論模式與實驗法。由選擇出正確的理論模式後,嘗試辨明高性能混凝土對氯離子擴散性的影響並瞭解礦物添加物(波索蘭材料)對氯離子擴散性的影響。由研究成果顯示對於擴散槽試驗法自然擴散是以半穩態形式影響擴散行為,而電場加速移動則是以暫態形式影響到擴散行為。對於傳統兩槽式加速擴散試驗,在本文中首度嘗試將氯離子在陽極待測槽會結合成氯氣之消耗特性放入方程式中;結果顯示修正後所得之擴散係數與三槽試驗較接近,且較未修正前二槽方程式所求得之擴散係數為低。並且發現消耗源係數在同一電場強度下與混凝土品質無關,而對不同電場強度下該係數與電場強度成正比。由本研究顯示以三槽試驗法可以避免氯離子被陽極消耗的問題,而二槽試驗法確有氯離子消耗的問題,但是採用修正的方程式仍然可以得到與三槽類似的擴散係數。本研究也發現量測氯離子的精度影響到對擴散行為的判斷,僅有在足夠精度下才會發現傳統二槽式擴散試驗法需加入消耗源的修正項。本研究顯示氯離子擴散係數隨著混凝土強度上昇而下降,以波索蘭材質取代水泥可以降低擴散性;以接近強度之混凝土相比較時可發現有添加水淬爐石粉可以降低擴散性。 The main goal of this study is to identify the correct physical models and experimental methods for the accelerated chloride diffusion in concrete. By using the suitable method, the influence of concrete strength and pozollans on chloride diffusivity is examined. The results show that the natural diffusion process in concrete is in term of quasi-steady state and ions' migration due to the electrical field is in term of non-steady state. For the two-chamber accelerated test, the modified equation by adding a sink, which describes the electrochemical reaction; two chloride ions lose two electrons and combine into chloride gas, is first proposed in this study. The results show the diffusion coefficient obtained by using this modified equation is much closer to that obtained from three-chamber accelerated test, and the diffusion coefficient obtained from this modified equation is lower than that obtained from unmodified equation. Furthermore, the sink coefficient is found to be independent on the concrete property under the same electrical field intensity and linear proportional to the electrical field intensity. The three-chamber accelerated test can avoid chloride consumption problem where two-chamber accelerated test cannot do; however, if the modified equation involving the sink is used, similar diffusion coefficients can be obtained for these two experimental methods. Also it is found that the precision of chloride measurement can influence our judgement of using which mathematical model to describe the diffusion phenomenon. Only while the measurement precision is enough, one can find the sink term is obvious. Test results show the chloride diffusion coefficient decreases as the concrete compressive strength increases. Pozzolan replacement can decrease the diffusion coefficient. Comparing to the diffusion coefficient of the similar compressive strength concrete, the blust slag can significantly lower the diffusion coefficient.

Keyword(s)

高性能混凝土
物化性質
氯離子擴散係數
High performance concrete (HPC)
Physicochemical property
Chloride diffusion coefficient

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A Study of the Chloride Diffusion Coefficients of HPC (I)

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