Benefits of chemical prestressing over mechanical prestressing of FRP rods

This paper presents a comparison of mechanical and chemical prestressing of fibre reinforced polymer (FRP) rods. Prestressing can be a solution to improve serviceability performance of FRP. However, current research is mainly focused on costly carbon fibre reinforcement rod (CFRP) chemical prestressing, whereas glass fibre reinforcement rod (GFRP) with established durability tests and proven serviceability limit for 100 years could be a potential economical option. Split wedge anchors for mechanical prestressing prevents notching of the FRP tendon and proved to be more effective. Chemical prestressing was investigated as a preferred option whereas anchors for FRP still require further development. In this case, expansion in concrete with special additives helps to generate tension in concrete reinforcement and prestress steel or FRP rebar. Expansive high-performance concrete (HPC) during chemical prestressing can provide similar expansion as mechanical anchors. Tensile properties of expansive mortar can be highly influenced by restraint. Higher cracking strain capacity, non-linearity and substantial plastic deformation can be achieved. The restrained expansive concrete undergoes much larger plastic deformation before cracking as well as residual deformation after failure because of bonding with rebar. Chemical prestress results of internal steel and CFRP can help to define a method of prestressing GFRP. Literature review proved that chemical prestressing with CFRP achieved 70% self-prestress. This development creates possibilities for more common GFRP rods and non-corrosive pretensioned reinforcement, avoiding complex pretension methods.