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Concrete In Australia : June 2014
38 Concrete in Australia Vol 40 No 2 FEATURE: FIBRE REINFORCED POLYMER 100 mm to 152 mm and the height varied from 152 mm to 762 mm, with the majority of the specimens having a 152 mm diameter and 305 mm height. The average compressive strength of the concrete ranged from 35 to 120 MPa with all batches of concrete mixed and cured at The University of Adelaide. The majority of the CFFT specimens were prepared using a manual wet lay-up process by wrapping epoxy resin impregnated fibre sheets around precision cut styrofoam templates. Only the specimens with fibres oriented at an inclined angle were selected to be manufactured using an automated filament winding process, which was performed at the University of Alberta in Canada. Specimens not manufactured as CFFTs were prepared as FRP-wrapped specimens, where a thin layer of epoxy resin was applied to the concrete surface prior to manually wrapping the fibre sheets around precast concrete cylinders. All CFFTs and FRP-wrapped specimens constructed using the manual wet lay-up technique had fibre sheets oriented in the hoop direction with at least 100 mm overlap unless otherwise indicated. The CFFT specimens manufactured by an automated filament winding process had fibre winding angles of 45, 60, 75 and 88 degrees relative to the longitudinal axis to examine the influence of fibre orientation. The type of fibre used in this experimental program included aramid and carbon FRP (AFRP and CFRP), with examples of these fibres shown in Figure 1. The epoxy adhesive consisted of two parts, epoxy resin binder and thixotropic epoxy adhesive, which were mixed at a ratio of 3:1. FRP coupons, with 25 mm width and a clear span of 138 mm length, were manufactured and tested in parallel to the FRP-confined concrete specimens in accordance with ASTM standard D3039M-08 (ASTM, 2008). Examples of the manufacturing methods of the FRP- confined concrete specimens are shown in Figure 2. The manufacturer-supplied material properties of the unidirectional fibre sheets and the fibres used in the manufacture of the filament wound tubes are shown in Table 1, together with the properties determined from coupon tests. The specimens were prepared using two different grades of concrete, namely NSC and HSC. In this paper, unconfined concrete strength (f’ co ) below 55 MPa is referred to as NSC and over 55 MPa as HSC. In designing the FRP confinement, due consideration was given to the well understood influence of the strength of concrete on its confinement demand (Ozbakkaloglu 2013c; Ozbakkaloglu & Vincent, 2013). This was done by selecting the number of FRP layers dependent on concrete strength with higher strength concrete specimens receiving proportionally more layers to ensure adequate confinement. Provided by manufacturer Obtained from coupon tests Type Nominal fibre thickness (mm) Ultimate tensile stress (MPa) Ultimate tensile strain (%) Elastic modulus (GPa) Ultimate tensile stress (MPa) Ultimate tensile strain (%) Elastic modulus (GPa) Aramid sheet type 1 0.2 or 0.3 2600 2.2 118.2 2390 1.86 128.5 Aramid sheet type 2 0.2 2900 2.5 120 2663 2.12 125.7 Aramid filament used in wound tubes 2930 2.9 99 Carbon 0.117 3800 1.55 240 3626 1.44 251 Table 1: Material properties of fibres. (a) (b) (c) (d) Figure 1: Materials for manufacturing FRP-confined specimens: (a) unidirectional aramid fibre sheet; (b) unidirectional carbon fibre sheet; (c) mixing epoxy resin; (d) preparing epoxy resin for application. 37-45 - Vincent.indd 38 37-45 - Vincent.indd 38 22/05/14 3:05 PM 22/05/14 3:05 PM