ICE methodology for FRP characterisation

The use of externally bonded FRP-systems is an effective retrofitting technique widely recognized to increase strength and deformability of reinforced concrete columns. With the expanding use of FRP jacketing, accurate prediction in performance for design purposes becomes increasingly important, achieved through well characterised materials. A critical parameter in predicting the ultimate behaviour of FRP confined concrete is measured with the ultimate FRP tensile strain, determined from material direct tensile tests. However, ultimate FRP tensile strain determined experimentally according to flat coupon tests has not been reached at the circumferential (hoop) rupture of FRP jackets confining concrete cylinders. This paper presents the development of a novel 'Investigation of Circumferential-strain Experimental' (ICE) methodology for FRP characterisation, aimed at providing a reliable experimental technique to assess the ultimate hoop strain of FRP laminates. The ICE methodology uses the unique property of water that expands when it changes state of matter from liquid to solid, as a medium to apply an internal hydrostatic pressure replicating the effect of concrete columns subjected to axial loads. The method was first assessed on circular metal containers to assess its feasibility, and then validated on cylindrical Glass FRP specimens made of different diameters and laminate thicknesses. The results indicate that the proposed ICE methodology is a reliable test method generating statistically reproducible hoop strain measurements, while providing an effective test technique. Furthermore, average ultimate hoop strain results indicate a lower level of strain than those found in similar flat coupon specimens under direct tensile tension.