Deterioration of Concrete Exposed to Evaporative Transport Conditions

暴露于蒸发运输条件下的混凝土的劣化

• 批准号: RGPIN-2018-05915
• 负责人: Boyd, Andrew
• 金额: $ 2.62万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=712886
• 关键词: Deterioration; Concrete; Exposed; Evaporative; Transport

Most deterioration mechanisms in concrete require that an outside agent enter the concrete through the connected pore system. This deleterious material could be sulfates that attack the concrete directly, chlorides that cause corrosion of the reinforcing steel, or simply water that can initiate alkali-aggregate reactions or contribute to freeze-thaw damage. Deterioration rates are highly dependent upon the rate of penetration of the liquid in question. Being able to quantify this rate is critical toward predicting deterioration rates and thus service lives of structures. Most current models rely on diffusion as the primary mass transport property. However, evaporative transport can produce a far higher rate of penetration, thus making a diffusion-based model highly inaccurate. Evaporative transport occurs when part of a structure is exposed to moisture while a nearby portion is exposed to the atmosphere. This creates an evaporation surface that tends to draw water into the concrete and toward this surface at a rate that depends upon the evaporation rate of the water from the surface. Most structures exposed to water match this description; bridge piers protruding from the ocean, floor slabs on grade, and earth retaining walls are a few examples. Prior research by the applicant using magnetic resonance imaging (MRI) has shown that evaporative transport is a very complex mechanism that needs further study before it can be introduced into a service life model. In addition, evaluating the deterioration rate of concrete requires a new approach that relies on mechanical properties as opposed to indirect measurements like expansion. The applicant intends to use the tensile properties of concrete as a quantification medium for mechanical property deterioration. Since most deterioration mechanisms in concrete involve the development of internal expansive stresses that are tensile in nature, tensile strength is the most appropriate mechanical property for quantifying the magnitude of damage and the residual strength. The proposed research will tie these issues together by further evaluating the phenomenon of evaporative transport in concrete, developing an exposure regimen to create evaporative transport based deterioration, and devising an evaluation protocol based on the degradation in tensile properties. In general, the proposed research program will provide a better understanding of a very common transport mechanism found in concrete structures throughout the world. One could argue that evaporative transport is the MOST prevalent mechanism in deterioration. Being able to quantify its effects on deterioration, coupled with a standardized exposure and testing regime, would result in much more accurate service life predictions. This would allow for more sustainable design of structures, dramatically reducing material usage and lifecycle costs.

混凝土中的大多数劣化机制需要外部试剂通过连接的孔隙系统进入混凝土。这种有害物质可能是直接侵蚀混凝土的硫酸盐，导致钢筋腐蚀的氯化物，或者可能引发碱-骨料反应或导致冻融破坏的水。劣化速率高度依赖于所讨论的液体的渗透速率。能够量化这一速度是至关重要的预测退化率，从而结构的使用寿命。目前大多数模型依赖于扩散作为主要的质量传输属性。然而，蒸发运输可以产生更高的渗透率，从而使基于扩散的模型非常不准确。当结构的一部分暴露于湿气而附近部分暴露于大气时，发生蒸发输送。这产生了蒸发表面，该蒸发表面倾向于以取决于水从表面的蒸发速率的速率将水吸入混凝土中并朝向该表面。大多数暴露在水中的结构都符合这一描述;突出于海洋的桥墩、地面上的楼板和挡土墙是几个例子。申请人使用磁共振成像（MRI）进行的先前研究表明，蒸发运输是一种非常复杂的机制，在将其引入使用寿命模型之前需要进一步研究。此外，评估混凝土的劣化率需要一种新的方法，这种方法依赖于机械性能，而不是像膨胀这样的间接测量。申请人打算使用混凝土的拉伸性能作为力学性能劣化的量化介质。由于混凝土中的大多数劣化机制涉及本质上拉伸的内部膨胀应力的发展，因此拉伸强度是量化损伤程度和剩余强度的最合适的机械性能。拟议的研究将这些问题联系在一起，进一步评估蒸发运输的现象在混凝土中，开发一个暴露方案，以创建蒸发运输为基础的恶化，并设计一个评估协议的基础上，拉伸性能的退化。总的来说，拟议的研究计划将提供一个非常常见的运输机制在世界各地的混凝土结构中发现更好的理解。有人可能会说，蒸发运输是最普遍的机制，在恶化。能够量化其对劣化的影响，再加上标准化的暴露和测试制度，将导致更准确的使用寿命预测。这将允许更可持续的结构设计，大大减少材料使用和生命周期成本。