低放處置場工程障壁之溶出失鈣及劣化敏感度分析; Effects of leaching on cementitious material as barrier and parameter sensitivity analysis for low-level radioactive waste disposal

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题名:	低放處置場工程障壁之溶出失鈣及劣化敏感度分析;Effects of leaching on cementitious material as barrier and parameter sensitivity analysis for low-level radioactive waste disposal
作者:	邱怡瑄;I-Hsuan Chiu
贡献者:	土木工程研究所
关键词:	低放射性廢棄物處置場;混凝土障壁;失鈣劣化;low-level radioactive wastes;concrete barrier;leaching
日期:	2009-07-03
上传时间:	2009-09-18 17:28:16 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	低放射性廢棄物處置場工程障壁主體由混凝土構成，由於台灣處於四面環海環境下，使得低放射性廢棄物處置場可能遭受外在環境各種元素的侵蝕，處置場障壁長期處於此服務環境下，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溶出失鈣效應，利用水泥基材分別製作水泥漿、水泥砂漿及混凝土試體，針對不同環境探討環境變化下混凝土材料受溶出失鈣之影響，以純水及人工海水浸泡混凝土試體模擬不同環境情況下失鈣情形，並以硝酸銨溶液模擬加速失鈣劣化。試驗結果得知（1）利用SEM-EDS測量各配比不同深度鈣矽比，混凝土試體在硝酸銨溶液中的抵抗溶出失鈣效應較優於水泥漿及水泥砂漿試體；（2）隨著試體曝露時間增加，水泥基材料之容積比重降低，顯示其受溶出失鈣導致孔隙增加；（3）由微觀分析結果顯示，水泥漿試體浸泡硝酸銨溶液後會加速溶出氫氧化鈣，造成試體表面之重量嚴重損失，由熱重分析試驗、X光繞射分析試驗所觀測之水泥漿試體皆顯示鈣含量隨深度增加而降低。運用美國國家標準署4SIGHT程式模擬各參數對於混凝土劣化之影響，由參數敏感度分析結果顯示，組成因子、水灰比及卜作嵐材料用量等混凝土材料參數對於抵抗環境離子的入侵有相當重要的影響，且可以組成因子評估各混凝土材料參數的重要程度。此外，混凝土障壁在多種劣化機制共同作用下，將會加速環境離子的入侵速率，而影響工程障壁的服務年限。 The barrier for low-level radioactive wastes disposal structures calls for the use of concrete. Taiwan is surrounded by marine environment where low-level radioactive waste disposal sites may be subject to intrusion of various elements from the external environment. When the disposal sites are exposed to such condition, it may cause concrete deterioration and reduces its durability. This study focuses on the effect of leaching of concrete as simulated in the laboratory to assess the durability in long term use of concrete materials. The basic mixture for cements, mortar and concrete were used to produce test specimens that were exposed to different conditions such as pure water and artificial salt water to simulate calcium loss under different circumstances. The possible mechanism and potential influence of calcium loss and concrete durability were then carefully examined. The results of the extensive laboratory experiments had shown that : (1) concrete materials has better resistance against calcium leaching in ammonium nitrate compared to cement mortar and cement when SEM-EDS measurement on the Ca/Si ratio were used. (2) The increase in duration of exposure of cement mortars resulted in the increase in porosity of the specimen and resulted in the decrease of bulk density. (3) Microstructural observation showed that mortar samples in ammonium nitrate solution experience accelerated leaching of Ca(OH)2, resulting in the severe deterioration of the surface of the specimen. The use of thermogravimetric analysis and X-ray diffraction analyses shows that the calcium content of the cement specimen decreases with depth. Using the 4SIGHT program developed by NIST, the effects of the concrete deterioration were also evaluated. Parameter sensitivity analysis result had shown that formation factor, the water cement ratio and pozolanic material usage were essential in the resistance to chloride ions intrusion; it is also considered as an important formation factor in estimating the concrete material parameter. In addition, the concrete barriers would buckle under joint degradation mechanism, which would speed up the chloride intrusion rate, thus affecting the service life of the concrete barrier.
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