Assessment of mechanical and durability performances of NSC to self-healing FRC structural components under combined mechanical and environemental loadings

在恶劣的环境条件下，很大比例的普通强度混凝土(NSC)结构会出现早期劣化(如混凝土开裂或剥落、钢筋锈蚀等)。并且没有达到预期的寿命。这种早期的劣化主要是由于材料不足和结构设计标准不充分，没有考虑应用于结构的综合载荷(机械、热、化学载荷)的影响。要显著提高结构的耐久性，第一个有希望的方法是研制具有优异耐久性的混凝土，如纤维增强混凝土(FRC)和自修复混凝土(SHC)。第二种方法是评估在北方条件下发现的联合荷载下混凝土的力学和耐久性能。该研究计划的目标是：1)开发新一代自修复纤维混凝土(SHFRC)，2)评估和预测NSC到SHFRC在实际北方条件下的性能，3)制定允许显著延长结构耐久性的长期指南和设计标准。研究活动分为两个项目，涉及13名学生。项目A旨在通过确保愈合所需的水和未反应的化学外加剂的可用性来改善SHFRC的裂缝愈合。首先，在SHFRC中加入多孔集料和高吸水性聚合物，以吸收暴露条件下的水分，并将其分布在裂缝中，以利于愈合。其次，在SHFRC中，化学外加剂将被包裹在颗粒中，以限制其在裂缝形成之前的反应。B项目旨在评估在机械和热联合荷载作用下钢筋混凝土中的水和氯离子的传输机制(扩散、吸收和渗透)，以准确地模拟结构的使用寿命。首先，研究了恒定和循环机械荷载产生的裂缝对NSC、FRC和SHFRC传输机理的影响。其次，将研究机械和热荷载的联合作用对这些混凝土的传输机理的影响。第三，这些数据将用于开发一个再现裂缝模式和与传输机制相互作用的数值模型，以预测结构在荷载下的耐久性。这项研究计划通过两个创新和互补的研究项目来解决暴露的钢筋混凝土结构耐久性不足的关键问题。土木工程师目前忽视了NSC非常有限的治愈潜力。然而，高效SHFRC的研制将为它们提供新的材料，以提高结构的耐久性。土木工程师也忽略了结构上多个荷载的相互作用。考虑水和氯化物输送机制上的机械和热载荷引起的裂缝，将极大地改变结构的使用寿命预测，并表明必须对目前的结构设计方法进行修改。

Large proportion of Normal Strength Concrete (NSC) structures exposed to severe environmental conditions present an early deterioration (such as concrete cracking or spalling, rebar corrosion, etc.) and do not reach their expected lifetime. This early deterioration is largely resulting from deficient materials and inadequate structural design criteria not considering impacts of combined loadings (mechanical, thermal, chemical loads) applied to structures. A first promising method to extend significantly the durability of structures are to elaborate outstanding durability concretes, such as fiber reinforced concretes (FRC) and self-healing concretes (SHC). A second method is to evaluate the mechanical and durability performances of concretes under combined loadings found in northern conditions. The objectives of the research program are: 1) to develop new generations of Self-Healing Fiber Reinforced Concretes (SHFRC), 2) to evaluate and predict the performance of NSC to SHFRC under realistic northern conditions, and 3) to develop in long-term guidelines and design criteria allowing a significant extend of structures durability. Research activities are divided in two projects involving 13 students. PROJECT A aims to improve crack healing of SHFRC by ensuring availability of water and unreacted chemical admixtures required for healing. First, porous aggregates and superabsorbent polymers will be added in SHFRC to absorb water from exposure conditions and distribute it in cracks to favor healing. Second, chemical admixtures will be packaged in particles to limit their reaction before crack formation in SHFRC. PROJECT B aims to evaluate water and chloride transport mechanisms (diffusion, absorption and permeability) in reinforced concrete under combined mechanical and thermal loadings to model accurately service life of structures. First, the impact of constant and cyclic mechanical loadings creating cracks will be investigated on transport mechanisms of NSC, FRC and SHFRC. Second, the combined effect of mechanical and thermal loadings will be studied on transport mechanisms of these concretes. Third, these data will serve to develop a numerical model reproducing crack patterns and interactions with transport mechanisms to predict durability of structures under loads. This research program addresses the critical problem of inadequate durability of exposed reinforced concrete structures by two innovative and complementary research projects. Civil engineers neglect presently the very limited healing potential of NSC. However, elaboration of high-efficiency SHFRC will procure them new materials to improve durability of structures. Civil engineers also neglect interaction of multiple loadings on structures. Consideration of cracks caused by mechanical and thermal loadings on transport mechanisms of water and chlorides will change drastically service life predictions and demonstrate that the current design approach of structures must be modified.