Eco-Friendly Natural Basalt FRP for External Strengthening of Concrete Structures: Development of Constitutive Bond-Slip Laws and Design Models for Basalt FRP/Concrete Interface

自20世纪90年代后期以来，纤维增强聚合物（FRP）用于外部加固有缺陷的混凝土结构已在世界范围内被接受。当时生产的FRP由碳纤维（CFRP）、玻璃纤维（GFRP）和芳纶纤维（AFRP）等合成纤维组成，并用于建立有用的实验数据库，设计规范和标准在此基础上开发了设计模型（ACI 440.2R，CSA S806，CSA S6，fib TG5.1）。尽管在这一领域取得了进展，研究人员仍然面临着玻璃钢加固的问题，这些问题尚未得到研究界的适当关注：（i）不可再生资源的可持续性问题和对全球变暖的影响，这些资源在制造过程中需要更高的成本，并且对生态环境不友好;（ii）暴露于环境影响（例如，严酷的温度和耐火性）后，FRP/混凝土界面的耐久性;（iii）FRP/混凝土界面层的过早剥离;（iv）由于FRP的弹性行为直至最终破坏而引起的延展性问题。 因此，近年来研究界更加关注生态友好的天然纤维来制造FRP，作为CFRP和GFRP的替代品，例如玄武岩纤维（BFRP）。实际上，BFRP片材具有比GFRP更高的机械性能和更好的化学稳定性，比CFRP更低的拉伸强度但更高的断裂伸长率和更低的成本，以及高的耐火性、耐高温性和耐疲劳性。FRP/混凝土界面的粘结滑移行为是控制剥离破坏的关键因素，也是FRP对抗力的真实的贡献。此外，BFRP加固混凝土结构和BFRP/混凝土界面行为的研究很少，有些限制。因此，建议的研究旨在开发优化和合理的BFRP/混凝土界面设计模型，用于在静态和循环疲劳载荷下使用生态友好的玄武岩纤维加固混凝土结构。建议的方法将包括：（一）一个实验计划，包括双搭接剪切试验，研究BFRP/混凝土界面粘结行为和剥离机制，考虑各种相互依赖的参数的影响;（二）开发本构关系在BFRP/混凝土界面（粘结滑移关系）;和（三）开发BFRP/混凝土界面设计模型的基础上有限元建模和参数研究。 鉴于加拿大的结构状况，这项研究将提供生态友好的加固解决方案，以应对全球变暖，FRP耐久性和环境影响等可持续性问题。这将对建筑行业产生重大影响，并将允许在长期内为加拿大标准CSA S806和CSA S6（第16节）制定规范格式的设计方程。最后，这项研究将培养高素质的人才在加拿大建筑业内不断增长的领域。

The use of fibre reinforced polymer (FRP) for external strengthening of deficient concrete structures has been accepted worldwide since the late 1990s. The FRP produced at that time consisted of synthetic fibres, such as carbon (CFRP), glass (GFRP) and aramid (AFRP), and was used to build a useful experimental database on which design codes and standards have developed their design models (ACI 440.2R, CSA S806, CSA S6, fib TG5.1). Despite the progress made in the field, researchers are still facing issues with FRP strengthening that have not yet received proper attention from the research community: (i) sustainability issues and impact on global warming of the non-renewable resources which require higher cost during the manufacturing and are less eco-friendly; (ii) durability of the FRP/concrete interface after exposure to environmental effects, such as severe temperatures and fire resistance; (iii) premature debonding at the FRP/concrete interfacial layer; (iv) ductility issues due to the elastic behaviour of FRP up to ultimate failure. Therefore, the research community have given in recent years more attention to eco-friendly natural fibres to fabricate FRP as an alternative to CFRP and GFRP, such as basalt fibres (BFRP). Indeed, BFRP sheets have higher mechanical properties and better chemical stability than GFRP, lower tensile strength but higher elongation at break and lower costs than CFRP, high resistance to fire, elevated temperature, and fatigue. The bond-slip behaviour at the FRP/concrete interface is the key factor in controlling debonding failure and the real FRP contribution to resistance. Also, research studies on BFRP-strengthened concrete structures and the BFRP/concrete interfacial behaviour are few and somewhat limited. Therefore, the proposed research aims to develop optimized and rational BFRP/concrete interfacial design models for strengthening of concrete structures using eco-friendly basalt fibres, under static and cyclic fatigue loads. The proposed methodology will encompass: (i) an experimental program comprising of double-lap shear tests to study the BFRP/Concrete interfacial bond behaviour and debonding mechanisms, considering the effect of various interdependent parameters; (ii) develop constitutive laws at the BFRP/concrete interface (bond-slip relationships); and (iii) develop BFRP/concrete interface design models based on finite element modelling and parametric studies. Given the state of structures in Canada, this research will provide eco-friendly strengthening solutions dealing with the sustainability issues on global warming, FRP durability, and environmental impacts. This will have a significant impact on the construction industry, and will allow, in the long term, to develop design equations in a normative format for the Canadian standards CSA S806 and CSA S6 (section 16). Finally, this study will train highly qualified personnel in a growing field within the Canadian construction industry.