低放射性廢棄物處置設施之障壁主體由混凝土構成，但不同於一般混凝土結構物之用途，其服務年限需達數百年之久。此外由於台灣處於四面環海環境，使得低射性廢棄物處置場之場址可能位於濱海區域，處置場障壁混凝土長期處於此環境下，可能對混凝土造成劣化甚至影響其耐久性。 本研究主要探討混凝土材料受氯離子入侵之劣化，並使用氯離子濃度門檻值與信賴度的概念，預估鋼筋開始腐蝕之時間。以可能使用於高完整性承裝容器之H 配比、傳統配合設計方法ACI 配比與緻密配比，進行相關試驗與分析。 試驗結果顯示，低水膠比之混凝土內部結構較緻密，氯離子擴散路徑更為蜿蜒曲折，導致氯離子擴散係數較小，但氯離子在混凝土表層持續累積，造成曝露表層有較高的氯離子濃度。以擴散係數判別抵抗氯離子入侵之能力，H 配比優於ACI 配比。為推估氯離子引致之腐蝕劣化，依氯離子入侵濃度預估鋼筋開始腐蝕之時間，主要影響因素為擴散係數與時間m 因子。利用各配比於不同歷時時間濃度剖面進行殘差分析，並以信賴度之概念建立其擴散係數之區間，配合氯離子濃度門檻值與規範之保護層厚度，計算出鋼筋開始腐蝕之時間。 The structure of low-level radioactive waste disposal sites is mainly made of concrete. Different from the general purpose of concrete structures, the service life of the disposal sites is expected to be hundreds of years. In addition, Taiwan is surrounded by ocean, which suggests the disposal sites may be subject, therefore vulnerable, to the environment. When the disposal sites are exposed to such a condition in a long term, it may cause concrete deterioration and reduces its durability. This study focuses on the effect of chloride on concrete, and uses the chloride threshold to predict the time to initial corrosion of steel in concrete. Test and analysis include: 1) high integrity container of H mixture, 2) traditional ACI mixture and 3) denser mixture designs. The results show concrete internal structures with a low water-binder ratio are more compact, resulting in a lower chloride ion diffusion coefficient. However, chloride continuously accumulates, which causes a higher concentration on the surface. Based on the diffusion coefficient, H mixture is better than ACI mixture. To estimate the time to initial corrosion caused by chloride, two main factors are taken into consideration: the diffusion coefficient and time - m factor. Concentration profiles of chloride at different times are used for residual analysis. To define the acceptable range of the diffusion coefficient, we look into the threshold of the chloride concentration and the thickness of concrete, and further estimate the time to initial corrosion of steel in concrete.
