貯鹽試驗為常見耐久性試驗,而相關規範訂定最短取樣時間為90天,因此試驗過程曠日費時。本研究為使判斷混凝土耐久性的過程能夠縮短,透過加壓方式加速氯離子於混凝土中傳輸,稱為「壓力滲透試驗」。 本研究透過水膠比為0.55之混凝土、靜水壓力大小為3、5 kgf/cm2進行壓力滲透試驗,相同試驗時間下,比較有無靜水壓力以及各種參數(卜作嵐材料種類及取代率、混凝土抗壓強度等)對於氯離子傳輸行為的影響。最後以「氯離子侵入深度」以及「氯離子濃度累積速率」作為指標,建立壓力滲透試驗做為加速性試驗取代貯鹽試驗的基礎。 為簡化分析靜水壓力下氯離子傳輸行為,假設滲流對於氯離子傳輸的影響由擴散作用貢獻,以擴散方程式擬合壓力滲透試驗氯離子含量,可計算得到等效氯離子傳輸係數(Deq),然而擴散方程式與滲流-擴散方程式線型不盡相同,隨著試驗時間以及靜水壓力的增加,滲流影響越顯著,兩者線型差異越大,相關係數R2越低。本研究選取R2為0.900以上做為參考,於特定試驗條件下,能利用等效氯離子傳輸係數(Deq)取代滲流-擴散方程式。從7天試驗結果顯示,貯鹽試驗擴散係數(D)與壓力滲透試驗等效氯離子傳輸係數(Deq)有良好線性關係,因此透過D與Deq,即能建立貯鹽試驗與壓力滲透試驗之間的關係,且Deq數值大小亦能夠判斷混凝土耐久性,其判斷結果與擴散係數(D)相符。 若以「氯離子侵入深度」為指標,試驗結果顯示21天5 kgf/cm2壓力滲透試驗做為加速性試驗能取代90天貯鹽試驗;又以「氯離子濃度累積速率」為指標,亦能發現相同結果。
Salt ponding test is a common method for evaluating the durability of concrete. Due to that chloride ion requires considerable time to penetrate the concrete specimen(e.g., 90-day Salt ponding test), the salt ponding test is regarded to be a long-term test. In order to shorten the process of evaluating the durability of concrete, this study adopts hydrostatic pressure to accelerate the movement of chloride ion, and this method is defined as “Seepage pressure test”. To know the transmission behavior of chloride ion, the influences caused by hydrostatic pressures, pozzolanic material types, replacement rates and compressive strengths under the same duration of testing time are discussed in this study. Two hydrostatic pressures 3 and 5 kgf/cm2 and water-cement ratio of 0.55 are adopted in the experiments. By quantifying the influences, the seepage pressure test can be proved to be an accelerated test and able to substitute salt ponding test with the indexes like the depth of chloride ion penetration and the accumulation rate of chloride ion concentration. In order to simplify the analysis of the transmission behavior of chloride ion under hydrostatic pressures, it is supposed that the transmission behavior is contributed by the diffusion. Therefore, the diffusion equation is fitted to the chloride concentration data from seepage pressure test to obtain equivalent chloride transmission coefficient Deq. However, the curved shape of diffusion equation and convection-diffusion equation are not the same. With the testing time increasing, the greater the difference between the two curved shape will be, and the correlation coefficient R2 will decrease. In this study, the correlation coefficient R2, higher than 0.900, is taken as a baseline, to make sure Deq can be applied to substitute convection-diffusion equation and describe the transmission behavior of chloride ion under hydrostatic pressures. Moreover, the 7 days experimental results show that diffusion coefficient D and equivalent chloride transmission coefficient Deq have a good linear relationship. Therefore, it is expected that D and Deq can be used to establish the relation between salt ponding test and seepage pressure test. In addition, Deq can also be applied to determine the durability of concrete. By taking the depth of chloride ion penetration as the index, experimental results show that 21-day seepage pressure test, with 5 kgf/cm2 hydrostatic pressure, can be used to substitute 90-day salt ponding test. Similarly, by taking the accumulation rate of chloride ion concentration as the index, the experimental results show the same as above.
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