Extending infrastructure service life rather than demolishing and reconstructing, contributes significantly to the sustainability of the built environment, one of the major objectives of the EU long-term strategy. In fact, minimising the reconstruction of structures reduces the consumption of cement and natural resources, hence lowering the greenhouse gas emissions and enhancing resource efficiency. Not only does it reduce expenditure, but it also decreases disruption to the function of important structures, such as bridges.
External post-tensioning is a retrofitting technique often used to enhance the serviceability performance of Reinforced Concrete (RC) structures through reducing deformation and increasing stiffness as well as improving durability.
Fixing prestressed Fibre Reinforced Polymer (FRP) plates to the structural element and mobilising their prestressing force to the structure is one of the most popular post-tensioning techniques. In this technique the tensile force generated by a hydraulic jack - secured to the structure at one end and to the FRP bar/laminate at the other end - is used to prestress the FRP. A high concentrated force at the jack-to-structure connection risks the local failure in concrete, which is a practical concern especially in post-tensioning of aged and deteriorated structures. Moreover, in such cases, the high FRP strength cannot be fully exploited since the premature concrete cover detachment will often be the prevailing failure mode. Temperature sensitivity and low ductility of FRP systems are other concerns.
The application of Shape Memory Alloys (SMA) for post-tensioning of structures is a recent promising development. SMA possesses a unique feature that enables it to recover its original shape by increasing its temperature once deformed plastically. The electrical resistivity of the alloy can be used to increase its temperature by passing an electrical current through it. Shape recovery under a restraint condition generates sufficiently large forces in the SMA element, suitable for post-tensioning applications. The emergence of the cost-competitive Iron-based Shape Memory Alloys (Fe-SMA) in recent years is a promising development that broadens the application of SMA’s in structural strengthening practices.
In this project, an innovative rapid post-tensioning retrofitting system is conceptualised, and its feasibility and performance efficiency are validated by employing complex experimental and numerical studies. This innovative system, designated “SMArtPlate”, is a thin prefabricated plate made of an Ultra-Ductile Mortar reinforced by SMA rebars. The high bearing capacity of the Ultra-Ductile Mortar facilitates the use of mechanical fasteners to attach SMArtPlate to the RC structure while its self-controlled crack width ensures an enhanced durability performance compared to the existing techniques.
