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

混凝土本质上是一种脆性材料，具有较低的拉伸强度和应变能力。从结构角度来看，可以通过添加钢筋来承受所施加的拉伸载荷来克服这一问题。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。由于有害物质更容易渗透到裂纹中，裂纹的引发导致加速劣化。此时，随着裂纹变宽或形成更多裂纹，劣化速度呈指数增加。此外，影响混凝土的大多数与耐久性相关的劣化过程都具有相似的基本破坏机制。内部膨胀导致拉应力，最终导致开裂。由荷载引起的拉应力和由耐久性相关的退化过程产生的拉应力应该是相加的，从而在协同作用时加速混凝土的退化速率。然而，标准耐久性测试不包括应力对劣化的影响，而是仅限于卸载的样本。这种情况导致对暴露于有害环境的混凝土的抗劣化性的严重高估。拟议研究项目的目的是评估将使用荷载与有害暴露条件相结合的效果，以便更接近地模拟结构中真实的混凝土劣化过程。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样本，以尝试开发更好的评估技术和标准来检查真实世界的结构。拟议研究的主要重点是开发一种系统方法来评估和量化由此产生的裂纹及其对机械和运输性能以及最终使用寿命的影响。

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.