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年代末以来，纤维增强聚合物（FRP）用于缺陷混凝土结构的外部加固已被全世界所接受。当时生产的FRP由合成纤维组成，如碳（CFRP），玻璃（GFRP）和芳纶（AFRP），并用于建立一个有用的实验数据库，设计规范和标准在此基础上制定了设计模型（ACI 440.2R, CSA S806, CSA S6, fib TG5.1）。尽管在该领域取得了进展，但研究人员仍然面临着玻璃钢加固尚未得到研究界适当关注的问题：(1)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，并且不太环保；（ii）玻璃钢/混凝土界面暴露于环境影响后的耐久性，如高温和耐火性；（iii） FRP/混凝土界面层过早脱粘；（iv）由于FRP的弹性行为导致的延性问题直至最终破坏。因此，近年来研究界更加重视利用环保的天然纤维来制造FRP，以替代CFRP和GFRP，如玄武岩纤维（BFRP）。事实上，BFRP片材具有比GFRP更高的机械性能和更好的化学稳定性，抗拉强度较低，但断裂伸长率较高，成本低于CFRP，具有较高的耐火性、耐高温性和抗疲劳性。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对阻力的真正贡献。此外，对BFRP增强混凝土结构和BFRP/混凝土界面性能的研究也很少，而且有一定的局限性。因此，本研究旨在开发优化合理的BFRP/混凝土界面设计模型，用于在静态和循环疲劳荷载下使用生态友好型玄武岩纤维加强混凝土结构。拟议的方法将包括：(i)一个由双搭接剪切试验组成的实验方案，以研究BFRP/混凝土界面粘结行为和脱粘机制，考虑各种相互依存参数的影响；（ii）制定BFRP/混凝土界面的本构规律（粘结-滑移关系）；（iii）基于有限元建模和参数化研究开发BFRP/混凝土界面设计模型。鉴于加拿大的结构状况，本研究将提供生态友好的强化解决方案，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，并且从长远来看，将允许以加拿大标准CSA S806和CSA S6（第16节）的规范格式开发设计方程。最后，这项研究将培养高素质的人才在加拿大建筑行业的一个不断增长的领域。

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.