Innovative Retrofitting of RC Structures Using Textile-Reinforced Alkali-Activated or Cement-Based Mortar Overlays: Application in Short Columns

The effectiveness of textile reinforced mortars (TRM) in the form of thin overlays applied on reinforced concrete (RC) members is shortly reviewed in the oral presentation of this work, with emphasis on recent findings by the authors, including the development of integrated TRM-thermal insulation systems for the combined seismic and energy retrofitting of existing structures. The possibility of replacing the standard ordinary Portland cement (OPC) matrix with an alternative environmentally friendly mortar based on alkali-activated materials (AAM) is also explored. As a case study, the paper covers the seismic retrofitting of short, shear-critical RC columns using OPC- or AAM-based TRM jackets. A total of seven columns were tested, at a scale of approximately 2/3, with the shear span – to – height ratio of 1.5. Four out of seven specimens were designed to be more ductile with closely spaced shear reinforcement, while the rest had their stirrups positioned at larger spacing. Both series of columns were retrofitted with two and four layers of TRM overlays, made of uncoated carbon textile and AAM- or OPC-based mortar, and subjected to cyclic loading combined with a constant vertical load. While control (unretrofitted) specimens exhibited brittle failure, the retrofitted ones performed significantly better in terms of deformation capacity, with a clear shift of the failure mode towards shear-flexure. All experimental findings were verified using analytical modelling, in good agreement with test results. Another interesting result is that AAM-based TRM jacketing is not inferior by any means to its OPC-based counterpart.