混凝土热-化学-损伤耦合模型与高坝碱骨料反应开裂研究

Alkali-Aggregate Reaction (AAR) is the leading cause of dam concrete deterioration, reducing the durability of the structure. AAR is a chemical reaction between amorphous silica present in reactive aggregate and alkali in pore solution. The principal manifestation of AAR is the formation of a hydrate gel, which swells by imbibition of free water and destroys the matrix bonds and causes fracturing of aggregates and the surrounding cement paste. AAR in the realistic structures usually needs a very long period of more than 10 years to take place. This slow-evolving internal concrete damage is causing millions of dollars of damage worldwide, whereas there is no (economically) feasible method to stop the reaction, though it can be mitigated to some extent. Concrete dams may meet a risk of suffering durability problem due to AAR during their operation period in the coming decades. In addition, a number of concrete dams are located in southwest China, where is a high seismic intensity zone. Therefore, an efficient numerical modeling is required for analyzing and predicting long-term expansion deformations and damage cracking of concrete dams subjected to AAR during operation period. Seismic safety of the AAR-affected concrete dams, in which AAR expansion deformation and cracking reduce the stability of the structure, is also needed to be assessed. .In the present work, a thermal-chemical-damage model for concrete is first proposed to analyze expansion deformation and damage cracking of AAR-affected structures at the macroscopic scale. The interaction among temperature field, stress field and chemical reaction process is investigated. Subsequently, degradation of mechanical properties of concrete and mechanism of swelling in accordance with AAR are examined using the meso-scale discrete particle modeling. The mechanical properties deteriorate with AAR extent over time. The AAR swelling exhibits anisotropic at a certain stress state. The mechanical properties and the anisotropic swelling are then linked with the macro-scale modeling for analysis of AAR-affected structures during their long-term operation periods. Finally, a unified modeling is established by combining the thermal-chemical-damage coupling model with the seismic analysis modeling of arch dam-foundation system previously proposed by the applicant, and it is applied to predict deformations and damage cracking of concrete dams subjected to AAR and assess the corresponding seismic safety.

碱骨料反应是损害大坝混凝土耐久性的主要原因之一，其表现为骨料所含的碱活性物质与水泥砂浆中的碱溶液发生化学反应，产物吸水膨胀，导致混凝土骨料和砂浆开裂。在未来的几十年内，我国混凝土坝存在碱骨料反应的风险。另外，我国很多高坝建于高地震烈度区。因此，需建立有效的数值模型分析和预测混凝土坝因碱骨料反应引起的变形与开裂，并校核其抗震安全性。.本项目拟研究温度场、化学反应过程、应力场的耦合问题，建立分析宏观结构碱骨料反应膨胀和开裂的混凝土热-化学-损伤耦合模型；基于颗粒离散元细观模型研究碱骨料反应过程材料力学参数退化与各向异性膨胀机制，为宏观模型提供可靠的材料参数，为结构提供各向异性变形准则；在拱坝系统抗震分析模型中引入热-化学-损伤耦合模型形成拱坝长期碱骨料反应与地震响应的统一分析模型。成果可用于遭受碱骨料反应病害的混凝土坝膨胀变形和损伤破坏的分析与长期预测，评价其运行过程中各阶段的抗震稳定性。

碱骨料反应是损害大坝混凝土耐久性的主要原因之一，其表现为骨料所含的碱活性物质与水泥砂浆中的碱溶液发生化学反应，产物吸水膨胀，导致混凝土骨料和砂浆开裂，从而造成结构稳定安全性受到损害。碱骨料反应一般持续数年，乃至数十年，对混凝土结构的危害是长久的。随着我国混凝土坝不断投入服役运行，在未来的30~50年，这些混凝土坝存在遭受碱骨料反应危害的风险。另外，我国很多高坝建于西南高地震烈度区，其服役生命周期内，极有可能遭受地震的考验。因此，混凝土坝长期服役碱骨料反应危害，以及受损混凝土坝抗震安全性问题，亟待进行深入的研究。本项目建立了混凝土细观碱骨料反应模型，研究了混凝土碱骨料反应引起材料细观损伤演化过程，揭示了碱骨料反应的膨胀机制及其引起混凝土材料劣化的机理，建立了碱骨料反应造成混凝土力学性能降低与碱骨料反应程度的关系，搭建了细观与宏观材料碱骨料反应损伤演化之间的桥梁；基于细观分析结果，建立了化学、力、热多场耦合的混凝土坝全生命周期细宏观跨尺度热-化学-损伤模型，分析和预测了碱骨料反应作用下混凝土坝长期服役的工作性态；建立了碱骨料反应混凝土坝长期性态和瞬态抗震分析统一模型，研究了老化混凝土坝的抗震安全性。该项目研究成果极大地促进了混凝土碱骨料反应与大坝长期服役老化研究理论水平的提高，加深了对混凝土碱骨料反应劣化机理和老化大坝服役工作性能的认识。