本研究針對硫酸鹽入侵混凝土結構之後所產生的耦合劣化機制進行探討。除了硫酸鹽離子在混凝土結構中的濃度擴散機制之外，硫酸鹽離子亦會與水泥材料中的鋁酸鹽進行二級化學反應，並產生具有膨脹性質的產物鈣礬石；鈣礬石的生成將造成混凝土結構的膨脹開裂，進而提高硫酸鹽在混凝土結構中的擴散率，加速結構產生的膨脹速率。
對於此耦合劣化機制的數值模擬，本研究利用有限元素軟體ABAQUS對於此擴散─反應機制進行分析，求解硫酸鹽與鋁酸鹽濃度在空間上與時間上的分佈趨勢，並採用膨脹計算理論(Tixier 2000)進行膨脹量的數值計算。
進行數值模擬與參數分析後，可得到以下結論：(1)此耦合擴散─反應機制的濃度分佈趨勢主要是由硫酸鹽擴散率控制而非反應速率常數；(2)混凝土試體的斷面大小將影響此耦合劣化機制所耗費的時間；(3)試體的最大膨脹量由鋁酸鹽初始濃度控制，但會因混凝土的毛細孔隙率及抗拉強度等材料特性而有所折減。

This main topic in this study is to discuss the coupled deterioration processes of concrete structures subjected to external sulfate attack. In addition to the diffusion process of sulfates in concrete microstructure, the second order reaction between sulfates and calcium aluminates in cement is also considered. The product of this second order reaction is ettringite, which has the expansive nature and will cause the expansion of concrete, thus increases the diffusivity of sulfates in concrete and the rate of expansion of the structure.
To simulate the coupled deterioration processes, the diffusion-reaction approach considered in this study is solved to find out the spatial and temporal distribution trend of sulfates and aluminates in concrete using the finite element software ABAQUS, the numerical computation of expansion is then performed adopting the theoretical model proposed in the reference (Tixier 2000).
After the numerical simulation and the parametric study, the following conclusions are obtained, (1) The concentration distribution solved in this coupled diffusion-reaction approach is mainly controlled by the diffusivity of sulfates rather than the rate constant of reaction. (2) The size of the concrete cross-section will significantly affect the total time cost in the coupled deterioration processes. (3) The maximum amount of expansion is controlled by the initial concentration of calcium aluminates, but reduced by the material properties of concrete such as capillary porosity and tensile strength etc.

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