Bridging the Gap from Lab to Field: Concrete Durability

根据2016年加拿大基础设施报告卡，大约33%的加拿大基础设施处于“一般”、“差”或“非常差”的状态。更具体地说，在75000座公路桥梁中，有33%存在结构或功能缺陷，使用寿命低于预期，降低了结构安全性，给经济、环境和社会带来了负担。耐久性通常是根据加速实验室试验来评估的。然而，在控制良好的实验室条件下评估的长期耐久性与现场混凝土结构的实际条件之间存在脱节。进行加速耐久性试验的实验室试样不考虑加固、约束、施加压缩或拉伸应力或暴露于耦合退化机制的存在。申请人提出了一种三管齐下的方法，将提高将混凝土耐久性实验室研究结果转化为混凝土结构现场耐久性的能力。三个短期目标是：1)评估内部膨胀反应机制对混凝土各向异性行为的影响，这是由于多种因素造成的，包括：浇筑方向、试件形状、骨料类型和钢筋的存在。2)确定实验室测试程序，包括条件反射和排序，鼓励悲观（最坏情况）行为，这些行为将被应用并用于促进对混凝土性能耦合降解机制的理解。3)确定应力施加对混凝土试件内部膨胀反应（碱硅反应）的影响和相应的机制，以及对混凝土损伤和使用寿命的估计。本研究计划的长期目标是开发：1)用于检查，测试和预测现有结构的新协议，这些结构解释了混凝土的各向异性行为；2)新的实验室测试规范（即MTO， CSA， ASTM），以评估混凝土暴露于耦合耐久性机制；3)基于加筋和机械荷载混凝土试件的性能和特性，对混凝土结构进行更准确的使用寿命预测。这将有效地弥合上述实验室混凝土耐久性测试的解释与结构的现场性能之间的脱节。该研究项目的主旨是对当前研究进展的补充，对加拿大工业、设计师、业主和混凝土基础设施运营商具有实际意义。这一领域的进步将减少与耐久性相关的结构故障，改善现有结构的诊断/预测，并使新的混凝土基础设施的设计比以往任何时候都具有更长的使用寿命。这对经济和环境都有利。

Based on the 2016 Canadian Infrastructure Report Card, approximately 33% of Canadian infrastructure is in fair, poor or very poor' condition. More specifically, 33% of 75,000 highway bridges are structurally or functionally deficient, yielding shorter service lives than anticipated, diminishing structural safety and burdening the economy, environment and society. Durability is commonly evaluated based on accelerated laboratory tests. However, there is a disconnect between long-term durability evaluated under well-controlled laboratory conditions and the actual conditions of concrete structures in the field. Laboratory specimens subjected to accelerated durability tests do not consider the presence of reinforcement, restraint, application of compressive or tensile stress or exposure to coupled degradation mechanisms.The applicant proposes a three-pronged approach that will improve the ability to translate results from laboratory studies of concrete durability to field durability of concrete structures. The three short-term objectives are to:1) Evaluate the effect of internal swelling reaction mechanisms on the anisotropic behavior of concrete due to a variety of factors including: casting direction, specimen shape, aggregate type, and presence of reinforcement.2) Identify laboratory test procedures including conditioning and sequencing, that encourage pessimum (worst case) behavior which will be applied and used to advance the understanding of coupled degradation mechanisms on concrete performance.3) Determine the implications and corresponding mechanisms of stress application to concrete specimens undergoing internal swelling reactions (alkali silica reaction and on concrete damage and service life estimates.The long-term goals of this research program are to develop: 1) new protocols for the inspection, testing, and prognosis of existing structures that account for the anisotropic behavior of concrete; 2) new laboratory test specifications (i.e. MTO, CSA, ASTM) to evaluate concrete exposed to coupled durability mechanisms; and 3) more accurate service life predictions of concrete structures based the performance and properties of reinforced, mechanically loaded concrete specimens. This will effectively bridge the aforementioned disconnect between the interpretation of laboratory concrete durability tests and the field performance of structures.The thrust of this research program complements current advances in research, and is of practical interest to Canadian industry, designers, owners, and operators of concrete infrastructure. Advancements in this area will result in fewer durability-related structural failures, improve diagnosis/prognosis of existing structures, and will enable the design of new concrete infrastructure to have longer service lives than ever before. This is both economically and environmentally beneficial.