| 摘要: | 在過去的幾十年中大量高放射性廢棄物(High level waste, HLW)不斷產出，核能電廠用於放置高放射性廢棄物之臨時處置設施的儲存容量已經接近飽和狀態，高放射性廢棄物面臨最終處置的問題。深地層處置設施(Geological disposal facility, GDF)概念是將最終處置場建置在地表以下200 m ~ 1200 m之間，通過工程障壁結構(Engineered Barrier Systems, EBS)為中心理念進行設計，其中必須使用大量水泥系材料進行建造。由於普通水泥系材料具有高鹼性且高鹼溶液將會影響作?緩衝材料之膨潤土性能，故用於最終處置場內之低鹼性水泥系材料孔隙溶液pH值必須低於11。
本研究之主要目的為以本土常見材料製作低鹼性混凝土，並為後續擬定相關標準提供參考。首先製作低鹼性一般混凝土、低鹼性自充填混凝土以及低鹼性噴凝土共計製作15組配比。膠結材料的使用比例中，前兩者水泥、矽灰及飛灰之比為5:4:1；低鹼性噴凝土則為4:2:4。通過對新拌、硬固、耐久以及水密性質進行工程性質之分析，探討其總膠結材料用量以及用水量的變化對不同類型混凝土工程性質之影響，並結合國際文獻分析該低鹼性混凝土的運用情況。其次利用MX-80與SPV 200膨潤土模擬最終處置場之現場環境，探討pH值在7 ~ 13.5範圍內以及常溫(23±1 ℃)、中溫(50±1 ℃)與高溫(80±1 ℃)之環境下對其膨脹性能之影響；同時驗證低鹼性混凝土孔隙溶液是否可以減少對膨潤土之影響。
結果顯示，不同類型低鹼性混凝土皆需借助強塑劑才可達到符合工作性之範圍內，使用的比例在1.3 % ~ 3.5 % 之間；pH值在齡期90天時除了低鹼性噴凝土外，皆可降低至11以下；抗壓強度在約56天時發展完全，90天時最高可達約62 MPa；體積穩定性、抗硫酸鹽能力以及緻密性方面皆表現良好；其中，配比PC-LB350-W45、SCC-LB300-W29及SHC-LB330-W30之綜合表現在本研究三類混凝土中最佳。膨潤土之膨脹指數試驗結果顯示，pH值與溫度變化對膨潤土之膨脹性能有顯著影響，其需處於pH值小於11之環境下才可保證膨脹能力的穩定；且通過試驗證實，使用低鹼性混凝土可較普通混凝土而言顯著降低對膨潤土膨脹能力之影響。
;In the past decades, a large amount of high-level waste (HLW) has been continuously produced. Nuclear power plants are nearing full capacity for the temporary disposal facilities for HLW. The geological disposal facility (GDF) concept is to build the final disposal site between 200 m and 1,200 m below the surface and is designed with the engineered barrier systems (EBS) as the central concept, which requires the construction of a large volume of cement matrix materials. Because ordinary cement materials have high alkalinity and high alkalinity solution, and it will affect the performance of bentonite as buffer material, the pH value of the pore solution of low pH cement materials used in the final disposal site must be less than 11.
There are a total of 15 mixed designs. The ratio of cement, silica fume, and fly ash for low pH of general concrete and low pH of self-compacting concrete are 5:4:1, while the ratio of low pH of shotcrete (sprayed concrete) is 4:2:4. Then there was the study of bentonite, using MX-80 and SPV 200. The effects of different pH on the expansion properties of the samples were investigated under normal temperature (23±1 ℃), medium temperature (50±1 ℃), and high temperature (80±1 ℃), in the range of 7 ~ 13.5. At the same time, the effect of low-pH concrete pore solution on bentonite was verified.
The results show that the additive amount of superplasticizer in these concrete needs to be between 1.3 % and 3.5 %. Exception of shotcrete (sprayed concrete), the pH of all concrete can drop below 11 at 90 days. The compressive strength develops completely in about 56 days, and the maximum compressive strength is about 62 MPa in 90 days. Their volume stability, sulfate resistance, and compactness are excellent. Among them, the ratio of PC-LB350-W45, SCC-LB300-W29, and SHC-LB330-W30 had the best comprehensive performance. The experimental results of bentonite show that pH value and temperature change have a significant effect on the expansion property of bentonite. It needs a pH value of less than 11 to ensure the stability of the expansion ability. Moreover, the use of low-pH concrete can significantly reduce the influence on the expansion of bentonite. |
