- 學位論文
岩石風化之力學特性與微組構變化暨吸附二氧化碳能力之研究
Variation on mechanical characteristics and microstructure during rock weathering process associated with carbon dioxide fixation
摘要
風化作用為岩石弱軟化的主因，對於岩體工程設計及其安定性影響深遠。岩石風化不僅是影響工程生命週期的物理指數與力學特性的變化，更是影響地球萬物生息永續發展的化學組成的循環。本研究透過人工風化循環試驗，探求風化過程岩石指數及力學特性之關係，據以探討(1)風化循環岩石微組構與力學特性之變化之關係；(2)人工風化與碳循環之關係；以及(3)風化作用指標試驗及模擬驗證等研究主題，建立岩石風化程度與力學特性變化的關係，並深入探討岩石風化程度量化評估指標以及對應的吸附二氧化碳能力。 研究結果顯示，砂頁岩互層層面間的鍵結強度較弱，遇水後膠結物溶出而黏結強度下降，成為循環過程主要的破壞面，抗風化能力極低。大理岩循環過程方解石溶解，導致孔隙率及吸水率上升，晶粒間接觸變少，造成晶粒間黏結力下降，因此歷經循環後，岩材明顯的弱軟化。蛇紋岩循環過程會發生礦物溶解及礦物相轉變的作用。溶解作用導致晶粒間空隙增加而接觸變少，造成岩材弱軟化。而推論循環過程中相轉變形成的石英則有助於晶粒間之黏結，可增加晶粒間的黏結能力。因此在循環過程中抗風化能力及力學特性有週期性變化，且抗風化能力及力學強度皆有增加現象。 由砂頁岩及蛇紋岩吸附二氧化碳能力顯示，岩石中未形成碳酸鹽類的鎂元素及鈣元素，皆有吸附二氧化碳的能力，且碳化能力隨循環次數而增加。由蛇紋岩之吸附二氧化碳能力及力學參數之迴歸分析顯示，吸附二氧化碳能力與力學特性有高度相關。推論單一岩材乃因循環過程與二氧化碳作用形成礦物相轉變，導致一般指數及微觀組構變化，間接造成岩材力學特性之改變。 模擬分析結果顯示，大理岩介觀材料以及微觀顆粒的膠結強度會隨循環過程下降，而蛇紋岩介觀材料以及微觀顆粒的膠結強度會隨循環過程上升，此模擬結果與實驗所得相同。
並列摘要
In nature, weathering reduces rock strength and increases its deformability. It is, therefore, an important factor which needs to be considered for designing safe engineering structures. The rock weathering zone and degree of weathering are also important for geological investigation. This study aims to clarify weathering mechanism of rock and to determine the variation of the mechanical and the mineralogical properties during weathering process which produced by means of artificial circulations on rapidly changing of environmental temperature and moisture conditions. Test results show that intercalated of sandstone and shale has weak bonding strength for the inter-bed and weather rapidly as the cementing material dissolved in water. The plane paralleling the inter-bad is the critical one for weathering failure. For marble, calcite dissolves during artificial weathering cycle and leads to increase in porosity and water absorption. Rock strength is reduced due to descending grain contacts. For serpentinite, mineral dissolution and phenomenon of phase transition are observed during artificial weathering, which increases porosity in mineral grains and reduces the mineral contacts. We infer that the quartz formed from phase transition is helpful for the bonding between grains. Therefore, the strength of weathering resistance and mechanical properties exhibit cyclic variation with a raising trend. Test results for the capability of carbon dioxide adsorption show that magnesium and calcium in the intercalated of sandstone and shale and the serpentinite can absorb carbon dioxide with an increasing as the artificial weathering cycles. Results of regression analysis show that the capabilities of carbon dioxide adsorption highly correlate with their mechanical properties. It is believed that mineral phase transition occurs during artificial weathering process, leads to variation on physical index and microstructure of the rocks and changing their mechanical characteristics. Numerical simulation results show that the strength of the meso-scale specimen and compositional micro-grain for marble descend during artificial weathering process, and conversely for serpentinite, which match with laboratory results.