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

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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.