使用壓力滲透試驗探討混凝土中氯離子之滲透行為

Abstract

在探討混凝土耐久性實驗中，貯鹽實驗藉由擴散作用使氯鹽滲透進混凝土中，由氯離子的滲透狀況可以判斷混凝土的耐久性，但是齡期需要較長的時間。而常見的較快速試驗方法，使用電場來加速氯離子在混凝土中的遷移，本研究希望使用加壓的方式來加速氯鹽的滲透來縮短試驗齡期。 本研究使用壓力滲透的方式來加速氯離子的滲透，將滲透完之混凝土以厚度每0.5cm為單位，逐層量測各深度下氯離子濃度來探討不同試驗齡期及不同水灰比下氯離子在壓力作用下的遷移機制和滲透狀況，比較氯離子在壓力滲透試驗與貯鹽試驗的差異性與相關性。 由總氯離子含量的實驗結果來看，貯鹽實驗60天的總氯離子含量小於壓力滲透20天大於壓力滲透7天，60天貯鹽實驗之總氯離子含量相當於壓力滲透試驗13天之值。將濃度0.005%之深度定義為滲透深度，從滲透深度來看，貯鹽實驗60天之滲透深度在各水灰比皆大於壓力滲透20天，60天貯鹽實驗之滲透深度相當於壓力滲透試驗25天。藉由公式分析壓力滲透20天之氯離子滲透狀況，70%的總氯離子含量為滲透作用導致，30%為擴散作用所造成。

In the ponding test for concrete durability experiment, chloride ions are allowed to diffuse into concrete, with which concrete durability is assessed. One drawback of the test is that it takes pretty long time. This can be improved by application of electric field that accelerate chloride permeation into concrete. In this study, external pressure was applied to speed up chloride permeation to shorten the test time. This study applied pressure to accelerate chlorides permeation－ concrete with chlorides seepage got evaluated by a series of layers, each was in 0.5cm of thickness; under pressure, chloride concentration was measured at particular depths to be studied its shifting mechanism and its state of permeation at different trial times and at different W/B. The results were compared with those of the ponding test. The results came out as followed: the number of chlorides from 60 days of ponding test is smaller that of 20 days of pressured permeation, but larger than that of 7 days of the same one. The amount of chlorides from 60 days of ponding test is about equivalent to that from 13 days of pressure permeation. On a standpoint of permeation depth, with the depth of chloride permeation at its concentration of 0.005% as an indicator, the depth measured from ponding test of 60 days is deeper than that of 20 days of pressured permeation, and is about equivalent to that from 25 days of pressured permeation. The analysis performed with the formula presents the process of 20-day chloride permeation. It is concluded that 70% of total chlorides are brought about by permeation and 30% by diffusion.