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、较差或非常差的状况。更具体地说，75000座公路桥梁中有33%存在结构或功能缺陷，使用寿命比预期短，降低了结构安全性，给经济、环境和社会带来负担。耐久性通常根据加速实验室测试进行评估。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情况之间存在脱节。接受加速耐久性测试的实验室样本不考虑是否存在钢筋、约束、施加压应力或拉应力或暴露于耦合退化机制。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，这些因素包括：浇注方向、试件形状、骨料类型和钢筋的存在。2)确定包括调节和排序在内的实验室测试程序，这鼓励了悲观(最坏的情况)行为，这将被应用并用来促进对混凝土性能耦合退化机制的理解。3)确定对经历内部膨胀反应(碱-硅酸反应)的混凝土试件施加应力的含义和相应的机制，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：1)发展新的检查、测试和预测现有结构的方案，考虑混凝土的各向异性行为；2)新的实验室测试规范(即MTO、CSA、ASTM)，以评估暴露在耦合耐久机制下的混凝土；以及3)基于加固的机械加载混凝土试件的性能和特性，更准确地预测混凝土结构的使用寿命。这将有效地弥合前述对实验室混凝土耐久性测试的解释和结构现场性能之间的脱节。这项研究计划的主旨补充了当前的研究进展，并对加拿大工业、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有关的结构故障，改善对现有结构的诊断/预测，并将使新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。这在经济上和环境上都是有益的。

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.