低放射性最終處置設施之主體為混凝土，但不同於一般混凝土結構物之用途，低放射性最終處置設施的服務年限可能長達數百年之久。另外由於台灣環境氣候潮溼，四面環海，場址的選擇可能位於臨海區域且採用淺層處置，此環境利於腐蝕反應之發生，使得最終處置設施長期在此環境下可能產生劣化，進而影響混凝土長期耐久性。 本研究目的係針對低放射性最終處置設施之混凝土材料長期處於濱海環境及地表下等特有環境下，以實驗室模擬混凝土及水泥砂漿長期曝露於不良環境，探討氯離子侵蝕及失鈣等兩種劣化行為對於混凝土長期耐久性影響。試驗結果得知(1)水泥砂漿試體浸泡於硝酸銨中歷時3個月後殘餘抗壓強度約為原試體抗壓強度的35%至41%，顯示混凝土失鈣現象所產生的劣化後果相當嚴重；(2)由氯離子浸泡試驗(Ponding test)與加速氯離子試驗(ACMT)結果得知使用飛灰、爐石與矽灰等卜作嵐材料皆能有效改善混凝土抵抗氯離子入侵的能力，且以飛灰及爐石之改善效果更優於矽灰；(3)由微觀分析結果顯示，水泥砂漿試體浸泡硝酸銨溶液後會加速溶出氫氧化鈣，使水泥砂漿試體因失鈣而產生劣化。 此外，運用模擬程式推估氯離子入侵混凝土之濃度剖面與浸泡試驗所得實際氯離子濃度剖面十分接近，顯示使用傳輸模式可有效預估氯離子入侵混凝土之現象，未來可進一步發展，應用於低放射性廢棄物最終處置場混凝土障壁服務年限之推估。 The structure of final disposal site for low-level radioactive is mainly made of concrete. Being different from the use of the general concrete structures, the service life of the final disposal site is expected to be over 3 hundred years. In addition, due to the humid climate and coastal geography in Taiwan, the disposal site is likely to be located at coastal areas. For a shallow underground disposal site, the near-field is subjected to severe environmental conditions and resulting in degradation of the concrete. This research aimed at investigating the effects of the chloride ion ingress and leaching on the degradation and durability of concrete at the final disposal site, with emphasis on the influence of the severe environment in an underground coastal area. We learned from the tests that: (1)the residual compressive strength of mortar samples immersed in ammonium nitrate solution for 3 months reduced to 35%~41% of the original compressive strength, showing that the degradation of concrete by leaching is much detrimental; (2)according to the ponding test and ACMT test results, the replacement of a portion of cement with pozzolanic materials was found to effectively improve the concrete’s ability to resist chloride ingress, and the improving effects demonstrated by fly ash and slag were found to be better than silica fume; (3)the results of the microstructure observations showed that mortar samples in ammonium nitrate solution experienced accelerating leaching of CaOH2. In addition, the chloride ion ingress profiles predicted using a diffusion model were very close to the profiles obtained from the ponding test, indicating that the use of diffusion model is effective in predicting the phenomenon of chloride ingress to concrete. The model can be applied to predict the service life of concrete barrier of the final disposal site for low-level radioactive in the future.
