低放射性廢棄物處置場障壁受硫酸鹽侵蝕之劣化模式評估

The estimate of the degradation model of sulfate attacked barrier at low-level radioactive wastes field.

吳清哲(Ching-Je Wu)

指導教授 ： 黃偉慶

國立中央大學/工學院/土木工程學系/碩士(2006年)

摘要

低放射性廢棄物處置場主體由混凝土構成，台灣在四面環海情形下，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，而低放射廢棄物所含核種需經300年後，絕大部分才會自然消失，處置場障壁長期在此種服務環境下，可能對混凝土造成損害或劣化甚至影響其耐久性。
本研究針對低放射性廢棄物處置場所使用之混凝土材料，以實驗室模擬混凝土材料長期受硫酸鹽侵蝕下，探討混凝土材料長期在此環境下的行為，分析其可能劣化機制及對耐久性之影響。試驗結果得知(1)以卜作嵐材料取代部份水泥，能改善混凝土抗硫酸鹽侵蝕之能力；(2)受硫酸鹽侵蝕後，其侵蝕之深度及濃度皆隨著歷時時間增加，以卜作嵐材料取代部分水泥，能增加混凝土緻密性提升抗硫酸鹽侵蝕之能力；(3)混凝土在長期硫酸鹽侵蝕條件下，動彈性模數值隨著歷時時間而增加；(4)由微觀分析結果顯示，水泥漿體受硫酸鹽侵蝕之歷時下，其內部微結構明顯可發現侵蝕產物，造成試體剝落及開裂，而使用卜作嵐材料能明顯消耗水泥漿體中的氫氧化鈣含量，使得混凝土更加緻密。
此外，採用硫酸鹽侵蝕模型針對混凝土受硫酸鹽侵襲進行參數敏感度分析，結果顯示以擴散係數、C3A含量、硫酸鹽邊界濃度及水泥水化程度對硫酸鹽侵蝕影響程度最大。

關鍵字

低放射性廢棄物處置場 ； 混凝土障壁 ； 硫酸鹽侵蝕

並列摘要

The proposed low-level radioactive wastes disposal calls for the use of concrete. Since Taiwan is surrounded by the sea, the low-level radioactive wastes disposal site is very likely to suffer from the attack of different elements of the environment, specifically, sulfate attack. The attack of concrete material used at the low-level radioactive wastes disposal site by the sulfate was simulated in the laboratory to determine the long-term durability of concrete material. The possible degradation mechanism and potential influence on the durability were carefully examined in this study.
The results of the laboratory works shows that: (1)the replacement of a portion of Portland cement with pozzolanic materials was found to help the concrete to resist the sulfate attack; (2)after being attacked by the sulfate, the depth of sulfate penetration increases with elapsed time of sulfate attack; (3)the dynamic modulus of concrete under the attack of sulfate increased as the time elapsed; (4)shown by microstructural observations, the product of sulfate attack to concrete was found in the specimens obtained from the peel-off and cracked portion, and the consumption of calcium hydroxide in the body of concrete by pozzolanic materials makes the concrete more resistant to sulfate attack.
In addition, a parametric study on the development of sulfate attack was carried out using a computer program. The result shows that the diffusion coefficient of concrete, C3A content of cement, sulfate boundary concentration, and the degree of hydration of cement were found to have greater effects on concrete by sulfate attack.

並列關鍵字

low-level radioactive wastes ； concrete barrier

參考文獻

黃兆龍，1999，「混凝土性質及行為」，詹氏書局。

Aköz, F., Türker, F., Koral, S., and Yüzer, N. (1999), “Effects of raised temperature of sulfate solutions on the sulfate resistance of mortars with and without silica fume.” Cement and Concrete Research, Vol. 29, pp. 537-544

Aguilera, J., Martínez-Ramírez, S., Pajares-Colomo, I., Blanco-Varela, M. T., (2003), “Formation of thaumasite in carbonated mortars.” Cement and Concrete Composites, Vol. 25, pp. 991-996.

A1-Dulaijan, S. U., Maslehuddin, M., A1-Zahrani, M. M., Sharif, A. M., Shameem, M., and Ibrahim, M. (2003), “Sulfate resistance of plain and blended cements exposed varving concentrations of sodium sulfate.” Cement and Concrete Composites, Vol. 25, pp. 429-437.

Al-Amoudi, O. B. (2002), “Attack on plain and blended cements exposed to aggressive sulfate environments.” Cement and Concrete Composites, Vol. 24, pp. 305-316.