Bond between Fibre-Reinforced Polymer Tubes and Sea Water Sea Sand Concrete: Mechanisms and Effective Parameters: Critical Overview and Discussion

Using fibre-reinforced polymers (FRP) in construction avoids corrosion issues associated with the use of traditional steel reinforcement, while seawater and sea sand concrete (SWSSC) reduces environmental issues and resource shortages caused by the production of traditional concrete. The paper gives an overview of the current research on the bond performance between FRP tube and concrete with particular focus on SWSSC. The review follows a thematic broad-to-narrow approach. It reflects on the current research around the significance and application of FRP and SWSSC and discusses important issues around the bond strength and cyclic behaviour of tubular composites. A review of recent studies of bond strength between FRP and concrete and steel and concrete under static or cyclic loading using pushout tests is presented. In addition, the influence of different parameters on the pushout test results are summarised. Finally, recommendations for future studies are proposed.

Studies on Recycling Silane Controllable Recovered Carbon Fiber from Waste CFRP

During the production process of commercial carbon fiber reinforced polymers (CFRPs), a silane coupling agent is added to the carbon fiber at the sizing step as a binder to enhance the product’s physical properties. While improving strength, the silane coupling agent results in a silane residue on recovered carbon fibers (rCF) after recycling, which is a disadvantage when using recovered carbon fibers in the manufacture of new materials. In this study, the rCF is recovered from waste carbon fiber reinforced polymers (CFRPs) from the bicycle industry by a microwave pyrolysis method, applying a short reaction time and in an air atmosphere. Moreover, the rCF are investigated for their surface morphologies and the elements present on the surface. The silicon element content changes with pyrolysis temperature were 0.4, 0.9, and 0.2%, respectively, at 450, 550, and 650 °C. Additionally, at 950 °C, silicon content can be reduced to 0.1 ± 0.05%. The uniformity of microwave pyrolysis recycle treatment was compared with traditional furnace techniques used for bulk waste treatment by applying the same temperature regime. This work provides evidence that microwave pyrolysis can be used as an alternative method for the production of rCFs for reuse applications.

Fibre failure assessment in carbon fibre reinforced polymers under tensile loading using in situ synchrotron X-ray computed tomography

In situ synchrotron radiation computed tomography (SRCT) was used to compare the fibre damage progression in five configurations of (902/02)s carbon-epoxy coupons loaded to failure. The effects of different sizing types, surface treatments and fibre diameters on the macroscopic properties, for example, ultimate tensile strength (UTS), and on the damage accumulation at a microscopic scale, for example, fibre break accumulation, were assessed. A semi-automated approach was adopted to process the large amount of data obtained from the SRCT scans and further method applicability areas can be envisaged. Single fibre break accumulation was seen to be influenced by the fibre type, while the formation of interacting fibre break groups by the surface treatment and the sizing type. For the materials presented, it can be suggested that an increased defect tolerance can be obtained by moving from stronger to weaker fibre-matrix adhesion, with sub-critical multiplet behaviour emerging as independent of the average UTS value.

Experimental assessment of different strengthening techniques for opening in reinforced concrete beams

The present experimental study includes testing thirteen reinforced concrete beams with openings at different locations to investigate the efficiency of strengthening such openings. Different strengthening techniques around the opening after and before casting include diagonal bars, upper and lower steel, and carbon fiber reinforced polymers (CFRP), were examined. All beams were made from 30 MPa compressive strength and tested under four-point loading. The cross section of the beams is 400 mm depth x 160 mm width and beam length 2400 mm. The dimensions of the opening are 200 mm x 200 mm. The stiffness, deflection, failure load, and failure mode of the strengthened beams were discussed. Experimental results showed that the beams strengthened with upper and lower steel around opening at mid-span increase the load-carrying capacity by 16.59%. However, beams strengthened by CFRP sheets around the opening in the shear zone increase the load carrying capacity by 47.7% compared to opened beam.