Evaluating the Combined Effects of Stress and Exposure on the Deterioration Rate of Concrete

混凝土本质上是脆性材料，表现出低拉伸强度和应变能力。从结构的角度来看，这是克服了钢筋的增加，以承担所施加的拉伸载荷。然而，混凝土中仍然存在拉应力，并且在使用中相对容易开裂。开裂的开始导致加速劣化，因为有害试剂更容易渗透到裂纹中。在这一点上，恶化的速度随着裂纹的扩大或更多裂纹的形成而呈指数级增加。此外，大多数影响混凝土的耐久性相关劣化过程具有类似的基本破坏机制;内部膨胀导致拉伸应力，最终导致开裂。由荷载引起的拉应力和与耐久性相关的劣化过程引起的拉应力应是加性的，从而在协同作用时加速混凝土的劣化速率。然而，标准的耐久性测试不包括应力对劣化的影响，而是仅限于未加载的试样。这种情况导致严重高估了暴露于有害环境的混凝土的抗劣化能力。拟议的研究项目的目的是评估有害的暴露条件下，以更紧密地模拟现实世界的混凝土退化过程中的结构相结合的使用荷载的影响。这种组合方法在标准化耐久性测试领域确实是独一无二的。在暴露期间，还将使用无损技术定期监测试样，以尝试开发更好的评估技术和标准，用于检查真实世界的结构。拟议研究的主要重点将是开发一种系统的方法来评估和量化产生的裂纹及其对机械和运输性能的影响，并最终使用寿命。

Concrete is inherently a brittle material, exhibiting low tensile strength and strain capacities. From a structural viewpoint, this is overcome by the addition of reinforcing steel to carry applied tensile loads. However, tensile stresses are still present in the concrete and it tends to crack relatively easily in service. The initiation of cracking leads to accelerated deterioration as deleterious agents penetrate more readily into the cracks. At this point, the rate of deterioration increases exponentially as cracks widen or more cracks form. In addition, the majority of durability-related deterioration processes affecting concrete share a similar basic damaging mechanism; internal expansion resulting in tensile stresses that ultimately lead to cracking. Tensile stresses induced by loading and those resulting from durability-related deterioration processes should be additive, thus accelerating the degradation rate of concrete when acting in concert. However, standard durability tests do not include the effects of stress on deterioration, being instead limited to unloaded specimens. This situation results in a gross overestimation of the deterioration resistance of concrete exposed to deleterious environments. The intent of the proposed research project is to evaluate the effect of combining service loads with deleterious exposure conditions in order to more closely simulate real-world concrete deterioration processes in structures. This type of combined approach is truly unique in the area of standardized durability testing. During exposure, specimens will also be monitored on a regular basis using nondestructive techniques in an attempt to develop better evaluation techniques and criteria for the inspection of real-world structures. The primary focus of the proposed research will be to develop a systematic approach to evaluate and quantify the resultant cracking and its effect on mechanical and transport properties, and ultimately service life.