低放射性廢棄物處置場混凝土障壁材料溶出劣化效應評估

Effects of leaching on cementitious material as barrier for low-level radioactive waste disposal

潘奕銘(Yi-Ming Pan)

指導教授 ： 黃偉慶

國立中央大學/工學院/土木工程學系/碩士(2007年)

摘要

低放射性廢棄物處置場主體由混凝土構成，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，可能對混凝土造成損害或劣化甚至影響其耐久性。
本研究針對低放射性處置場所使用之水泥基材長期處於地下環境等特有環境下，以實驗室模擬水泥砂漿及水泥漿長期暴露於各種不同環境，探討溶出行為對於水泥基材長期耐久性之影響。試驗結果得知（1）不論浸泡於純水、人工海水或硝酸銨溶液之砂漿試體皆出現明顯的強度折減，其中尤以浸泡於硝酸銨溶液之試體強渡折減最為顯著；（2）隨著溶出歷時時間之增加，將降低其容積比重並使得孔隙率隨之增加，尤其又以浸泡於硝酸銨溶液中之水泥砂漿試體最為顯著；（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，造成試體表面之重量嚴重損失，皆由電子顯微鏡之能量分散光譜儀（SEM-EDS）、電子探微儀量及電子能譜儀所觀測之水泥漿試體皆顯示鈣含量隨深度增加而降低。
此外，運用美國國家標準署CEMHYD3D程式模擬各參數對於溶出失鈣劣化之影響，由掺料參數及水化參數結果顯示，添加卜作嵐掺料對於抵抗溶出劣化有較好之功效，在水化參數方面，隨著水化程度越高時，將降低其溶出速率。在劣化參數方面，結果顯示隨著溶出劣化程度之增加，將使得氫氧化鈣損失量持續增加。

關鍵字

混凝土障壁 ； 低放射性廢棄物處置場 ； 失鈣劣化

並列摘要

The engineering barrier of the proposed low-level radioactive wastes disposal calls for the use of concrete. Since Taiwan is surrounded by oceans, the low-level radioactive wastes disposal site is very likely to suffer from the attack of adverse environment. In this study, leaching of concrete material was simulated in the laboratory to evaluate the long-term durability of concrete material. The possible degradation mechanism and potential influence on the durability were carefully examined.
The results of the laboratory works show that：（1）the residual compressive strength of mortar samples immersed in ammonium nitrate solution for 3 months reduced to 38％~45％ of the original compressive strength. After soaking in both pure water and ocean water environment, the residual compressive strength of mortar reduced to 75％~95％ of the original compressive strength.（2）Increases in leaching duration of cement mortars resulted in decreases in bulk density and increases in porosity of mortar specimens. （3）Microstructural observations showed that mortar samples in ammonium nitrate solution experienced accelerating leaching of Ca(OH)2, and SEM-EDS and XPS analyses show that the depths of leaching observed on cement mortar specimens are found to be deeper than the cement paste specimens.
The effects of leaching on properties of cement paste were also evaluated using the simulation program developed by NIST. The addition of pozolanic material（fly ash）to cement paste mixes was found to improve the resistance of cement paste. And the higher the degree of hydration, the lower the damage of leaching on cement pastes.

並列關鍵字

low-level radioactive wastes ； leaching ； concrete barrier

參考文獻

盧秉瑋，「混凝土工程障壁之氯離子及失鈣劣化行為」，碩士論文，國立中央大學土木工程研究所，中壢（2006）。

吳清哲，「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」，碩士論文，國立中央大學土木工程研究所，中壢（2006）

Alonso, C., Castellote, M., Llorente, I. and Andrade, C. (2006), “Ground water leaching resistance of high and ultra high performance concretes in relation to the testing convection regime, ” Cement and Concrete Research , Vol. 36, pp. 1583-1594.

Agostini, F., Lafhaj, Z., Skoczylas, F. and Loodsveldt, H. (2007), “Experimental study of accelerated leaching on hollow cylinders of mortar, ” Cement and Concrete Research, Vol. 37, pp. 71-78.

Bentz, D.P., Garboczi, E.J. (1992), “Modelling the leaching of calcium hydroride from cement paste: Effects on pore space percolation and diffusivity, ” Materials and Structures, Vol. 25, pp. 523-533.