Experimental evaluation of concrete confined with hand laid carbon FRP grids

Abstract

In many cases structures serve in highly corrosive environments and as a result the service life of the elements is significantly reduced. An alternative could be the use of fiber reinforced composites. The skepticism behind using this material has to do with the lack of ductility. A different approach must be followed in the design of such structures to achieve a behavior similar to regular reinforced concrete. In this case failure should initiate and end in concrete with confinement providing ductility. This paper investigates concrete confinement through experimental testing of concrete specimens utilizing embedded custom made, hand laid carbon FRP (CFRP) grid. The grid was formulated into the shape of a tube and embedded in concrete specimens to evaluate the grid tube effect on concrete properties. Typically, the FRP material is applied externally using an adhesive. In this case the hand laid CFRP grid was pre-manufactured and was embedded into concrete. Standard sized cylindrical specimens were manufactured using hand laid CFRP grid. Some of the specimens were made using plain concrete and served as reference specimens. The specimens were loaded axially in compression. This allowed the evaluation of the extent to which the hand laid tubular shaped grid positively affected the ultimate capacity and deformation of concrete. This application is unique and its confinement effectiveness needs to be investigated and evaluated. Experimental results show a very significant change in the maximum capacity and deformability for confined concrete. Depending on the amount of CFRP reinforcement in the grid strands the enhancement in strength was between 42 % and 58 %. The deformability of the specimens with the hand laid CFRP grid was between 134 % and 196 % higher compared to the reference specimens, with higher values associated with higher amounts of the CFRP grid.