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，表现出低的抗拉强度和应变能力。从结构的角度来看，这是通过增加钢筋来承载所施加的拉伸载荷来克服的。然而，混凝土中仍然存在拉应力，在使用中往往相对容易开裂。当有害物质更容易渗透到裂缝中时，裂缝的萌生会导致加速恶化。在这一点上，随着裂纹的加宽或形成更多的裂纹，劣化速度呈指数级增加。此外，影响混凝土的大多数与耐久性有关的劣化过程都有类似的基本破坏机制：内部膨胀导致拉应力，最终导致开裂。加载引起的拉应力和与耐久性有关的劣化过程产生的拉应力应该是相加的，从而在共同作用时加速混凝土的退化速度。然而，标准的耐久性试验不包括应力对劣化的影响，而仅限于未加载的试件。这种情况导致了对暴露在有害环境中的混凝土的抗劣化能力的严重高估。该研究项目的目的是评估服役荷载与有害暴露条件相结合的效果，以便更接近真实世界中结构中的混凝土劣化过程。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，还将使用非破坏性技术定期监测样本，试图制定更好的评估技术和检查真实世界结构的标准。拟议研究的主要重点将是开发一种系统的方法，以评估和量化由此产生的裂缝及其对机械和运输性能的影响，并最终达到使用寿命。

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.