Evaluation of Accumulated Damage in Reinforced Concrete at Early Age

本研究的目的是评估混凝土早龄期因硬化和干燥收缩、热和水传递以及外部应力引起的累积损伤和微观断裂，并开发新的混凝土结构耐久性时变性能评估系统。提出了水泥在混凝土中水化活化能的估算方法。提出了任意温度、任意龄期水泥水化路径依赖模型。活化能与配合比阐明了水泥的活化能随温度的变化受水泥在混凝土中的分散程度控制。提出了混合比例与活化能之间的一般关系式。利用混凝土的抗拉刚度，提出了钢筋周围保护层混凝土因硬化、干燥、收缩和离析引起的累积损伤的评估方法。通过平均抗拉强度、平均拉伸塑性变形和粘结劣化来评价材料的抗损伤性能。混凝土中的水分运动与干缩提出了混凝土在新鲜状态和硬化后的水分运动预测模型，该模型影响混凝土的损伤和微观断裂。从混凝土的微观结构出发，阐明了混凝土中干燥水分运动与收缩的关系。

The objective of this study is to evaluate the accumulated damage and micro fracture in concrete caused by hardening and drying shrinkage, heat and water transfer and external stress at early age, and to develop the new system for evaluating the time-dependent performance for durability of concrete structures.1. Time-dependent and path-dependent hydration of cementThe evaluation method for activation energy of cement in concrete was developed. The model for path-dependent hydration of cement at any temperature and any any age was proposed.2. Activation energy and mix proportionIt was clarified that the activation energy representing temperature dependency of cement is controlled by the dispersion of cement in concrete. General relationship between mix proportion and activation energy was successively proposed.3. Evaluation of accumulated damageEvaluation method of accumulated damage caused by hardening and drying shrinkage and segregation in cover concrete around reinforcing bars was proposed with use of tension-stiffness of concrete. Resistance to the damage was also successively evaluated by average tensile strength, average tensile plastic deformation and bond deterioration.4. Water movement and drying shrinkage in concreteModel for predicting water movement in concrete at fresh state and after being hardened was proposed, which affects the damage and micro fracture in concrete. Relationship between water movement by drying and shrinkage in concrete was clarified based on the micro-structure of concrete.