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

暴露于恶劣环境条件下的大部分普通强度混凝土（NSC）结构存在早期劣化（例如混凝土开裂或剥落、钢筋腐蚀等）。并没有达到预期的寿命。这种早期劣化主要是由于材料不足和不适当的结构设计标准没有考虑施加到结构上的组合载荷（机械、热、化学载荷）的影响。显著延长结构耐久性的第一个有希望的方法是精心制作优异的耐久性混凝土，例如纤维增强混凝土（FRC）和自愈合混凝土（SHC）。第二种方法是评估混凝土在北方条件下的机械和耐久性能。 研究计划的目标是：1）开发新一代的自愈合纤维增强混凝土（SHFRC），2）评估和预测在现实的北方条件下的NSC SHFRC的性能，和3）制定长期的指导方针和设计标准，允许结构耐久性的显着延长。 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，将多孔骨料和高吸水性聚合物添加到SHFRC中以吸收暴露条件下的水并将其分布在裂缝中以促进愈合。第二，化学外加剂将被包装在颗粒中，以限制它们在SHFRC裂缝形成之前的反应。项目B旨在评估在机械和热荷载联合作用下钢筋混凝土中水和氯离子的传输机制（扩散、吸收和渗透），以准确模拟结构的使用寿命。首先，恒定和循环的机械载荷产生裂纹的影响将被调查的NSC，FRC和SHFRC的传输机制。其次，机械和热负荷的综合影响将研究这些混凝土的运输机制。第三，这些数据将用于开发一个数值模型，再现裂纹模式和相互作用与运输机制，以预测在负载下的结构的耐久性。 本研究计划通过两个创新和互补的研究项目来解决外露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非常有限的愈合潜力。然而，高效SHFRC的研制将为他们采购新材料，以提高结构的耐久性。土木工程师也忽略了结构上多重荷载的相互作用。考虑水和氯化物的运输机制上的机械和热载荷引起的裂纹将大大改变使用寿命的预测，并表明，必须修改目前的结构设计方法。

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.