Nano-CaO抑制膨润土的胀-缩行为
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摘要
高压实膨润土吸水后高度膨胀能提高其"自愈能力",同时也可能会对围岩和核废料金属罐产生损伤,故调控膨润土的胀缩性能具有重要的研究价值。通过掺入4%不同质量比纳米氧化钙(nano-CaO),抑制膨润土的胀-缩性能。结果表明,干密度1.40 g/cm~3纯膨润土的膨胀率为148%,收缩稳定后的收缩量为63.2%;添加4%纳米氧化钙后膨胀率为70%,收缩稳定后的收缩量为34.8%,说明纳米氧化钙可以抑制膨润土的胀缩行为。通过扫描电镜和XRD表征发现,纳米氧化钙与膨润土矿物发生水化反应后生成"针状"的胶凝物质,形成稳定的网状结构。另外,孔隙分布特性曲线表明,约束作用下纳米氧化钙水化"消失"会形成新孔隙,蒙脱石吸水膨胀后能充填部分孔隙;但受氧化钙水化作用的影响,蒙脱石膨胀受到抑制,仍会留下部分孔隙未能被充填。与初始压实状态相比,添加纳米氧化钙后尽管在一定程度上提高了其密实度,但没有纯膨润土膨胀充填的效果理想。
Highly-compacted bentonite can increase its self-healing ability after absorbing water, while it may also damage surrounding rock and copper canister of nuclear waste. Thus, it is of great value to regulate the swelling-shrinkage properties of bentonite. Nano-CaO(mass ratio) was added to inhibit the swelling-shrinkage properties of bentonite. The results show that the expansion rate of compacted bentonite with dry density of 1.40 g/cm~3 is 148% and the degree of shrinkage is 63.2%.The expansion rate and degree of shrinkage of bentonite when 4% nano-CaO added are 70% and 34.8% respectively. It indicates that nano-CaO can suppress the swelling-shrinkage behavior of bentonite. SEM and XRD tests are carried out, which showed that needle-shape cementitious material attached to clay particle was generated after the hydration reaction between bentonite and nano-CaO. In addition, pore distribution characteristic curve reveals that new pore will form after hydration of nano-CaO under constraint, some of which can be taken place by swelling montmorillonite. Meanwhile, the expansion of bentonite is suppressed for hydration effect of CaO, leading to some pore unfilled. Compared with the initial compacted state, the density is improved, but the filling consequence is not as expected by adding nano-CaO. Therefore, it is worthy of further research to study reasonable swell increment of mixture of nano-CaO and bentonite, and to explore the balance point of expansion and suppression.
Highly-compacted bentonite can increase its self-healing ability after absorbing water, while it may also damage surrounding rock and copper canister of nuclear waste. Thus, it is of great value to regulate the swelling-shrinkage properties of bentonite. Nano-CaO(mass ratio) was added to inhibit the swelling-shrinkage properties of bentonite. The results show that the expansion rate of compacted bentonite with dry density of 1.40 g/cm~3 is 148% and the degree of shrinkage is 63.2%.The expansion rate and degree of shrinkage of bentonite when 4% nano-CaO added are 70% and 34.8% respectively. It indicates that nano-CaO can suppress the swelling-shrinkage behavior of bentonite. SEM and XRD tests are carried out, which showed that needle-shape cementitious material attached to clay particle was generated after the hydration reaction between bentonite and nano-CaO. In addition, pore distribution characteristic curve reveals that new pore will form after hydration of nano-CaO under constraint, some of which can be taken place by swelling montmorillonite. Meanwhile, the expansion of bentonite is suppressed for hydration effect of CaO, leading to some pore unfilled. Compared with the initial compacted state, the density is improved, but the filling consequence is not as expected by adding nano-CaO. Therefore, it is worthy of further research to study reasonable swell increment of mixture of nano-CaO and bentonite, and to explore the balance point of expansion and suppression.
引文
[1]Komine H,Ogata N.Predicting swelling characteristics of bentonites[J].Journal of Geotechnical and Geoenvironmental Engineering,2004,130(8):818-829.
[2]Ye W M,Wan M,Chen B,et al.Temperature effects on the swelling pressure and saturated hydraulic conductivity of the compacted GMZ01 bentonite[J].Environment Earth Sciences,2013,68(1):281-288.
[3]Kaufhold S,Klinkenberg M,Dohrmann R.Comparison of the dry densities of highly compacted bentonites[J].Clay Minerals,2013,48(1):105-115.
[4]Ogata N,Kosaki A,Ueda H,et al.Execution techniques for high level radioactive waste disposal:IV design and manufacturing procedure of engineered barriers[J].Journal of Nuclear Fuel Cycle and Environment,1999,5(2):103-121.
[5]Karnland O,Olsson S,Nilsson U,et al.Experimentally determined swelling pressures and geochemical interactions of compacted Wyoming bentonite with highly alkaline solutions[J].Physics and Chemistry of the Earth,2007,32:275-286.
[6]陳文泉.高放射性废弃物深层地质处置缓冲材料之回胀行为研究[D].台北:台湾国立中央大学,2004.
[7]Villar M V,Lloret A.Influence of dry density and water content on the swelling of a compacted bentonite[J].Applied Clay Science,2008,39(1):38-49.
[8]Agus S S,Schanz T.A method for predicting swelling pressure of compacted bentonites[J].Acta Geotechnica,2008,3(2):125-137.
[9]刘云.纳米氧化物-膨润土混合物的水理特性研究[D].宜昌:三峡大学,2016.
[2]Ye W M,Wan M,Chen B,et al.Temperature effects on the swelling pressure and saturated hydraulic conductivity of the compacted GMZ01 bentonite[J].Environment Earth Sciences,2013,68(1):281-288.
[3]Kaufhold S,Klinkenberg M,Dohrmann R.Comparison of the dry densities of highly compacted bentonites[J].Clay Minerals,2013,48(1):105-115.
[4]Ogata N,Kosaki A,Ueda H,et al.Execution techniques for high level radioactive waste disposal:IV design and manufacturing procedure of engineered barriers[J].Journal of Nuclear Fuel Cycle and Environment,1999,5(2):103-121.
[5]Karnland O,Olsson S,Nilsson U,et al.Experimentally determined swelling pressures and geochemical interactions of compacted Wyoming bentonite with highly alkaline solutions[J].Physics and Chemistry of the Earth,2007,32:275-286.
[6]陳文泉.高放射性废弃物深层地质处置缓冲材料之回胀行为研究[D].台北:台湾国立中央大学,2004.
[7]Villar M V,Lloret A.Influence of dry density and water content on the swelling of a compacted bentonite[J].Applied Clay Science,2008,39(1):38-49.
[8]Agus S S,Schanz T.A method for predicting swelling pressure of compacted bentonites[J].Acta Geotechnica,2008,3(2):125-137.
[9]刘云.纳米氧化物-膨润土混合物的水理特性研究[D].宜昌:三峡大学,2016.