The Use of Auxetic Laminates as a Construction Material
: A study on the behaviour of confined concrete columns using Prepreg CFRP Auxetic Jackets

  • Sean-Paul Attard

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

The increasing use of Fibre Reinforced Plastics (FRPs) as retrofitting or repairing materials to structural elements, has led to advances in the development of in-situ techniques allowing flexibility in the application and choice of FRP type using either pre-impregnated resin or manually impregnating epoxy resin into the FRP laminae. Extensive work was carried out on reinforced concrete columns where FRP jackets, when wound around the surface of the columns, enhance the strength and ductility of these columns. Developments have shown that FRP laminates with particular stacking sequences exhibit auxetic behaviour. This was noted to occur in symmetric balanced angle-ply laminates, particularly with angles varying between 20° and 25°, where a negative Poisson’s ratio (NPR) was discovered to be either negative in-plane or through-thickness Poisson’s ratio.

In this research study, design oriented and analysis oriented confinement models were used to examine the behaviour of confinement jackets. These results were compared to compression tests carried out using a Force Control mechanism at a rate of 1kN/s. The SE70 CFRP prepreg, having a curing temperature of 70°C for 16 hours, was used for manufacturing the jackets using the conventional vacuum bagging system. The [±20]2s and [±25]2s configurations were chosen to inspect auxetic behaviour. To provide a suitable means of comparison to the auxetic jackets, other stacking sequences were tested, more precisely [±35,02]s and [±16,±45]s, that have the same Young’s modulus as the auxetic laminates tested, yet with a different Poisson’s ratio value. Confinement jackets holding the maximum and minimum Young’s modulus of elasticity respectively i.e. [08] and [908], were also examined. All confinement jackets, except [908], failed in an explosive manner. From the experimental tests, it was deduced that the auxetic confinement jackets performed best. This resulted due to the improved fracture toughness and increase in energy storage instigated by the through thickness expansion that were achieved with the presence of a negative Poisson’s ratio, that in turn contributed in enhancing the strength of a confined concrete column. In fact, the auxetic stacking sequence [±20]2s having NPR value of -0.403 and mean value failure stress of 148.24MPa showed gains of 387% in terms of compressive strength when compared with the control concrete cylinder. Similarly, a 351% gain was obtained for the auxetic stacking sequence [±25]2s having NPR value of -0.468, and a mean value failure stress of 134.15MPa.
Date of Award25 Jun 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorWendel Sebastian (Supervisor) & Fabrizio Scarpa (Supervisor)

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