Towards the Development of Pseudoductile FRP Rebar

• Author / Creator

  Ivey, Marcus A

• Steel has traditionally been used as the material of choice for concrete reinforcement, due in part to its combination of high strength, stiffness, and ductility. However, steel rebar is susceptible to corrosion when exposed to moisture and salts, which can lead to delamination between the steel and concrete, requiring costly repairs to prevent premature failure of reinforced structures. In order to solve this problem, non-corrosive fiber reinforced polymer (FRP) rebar can be used in the place of steel. Apart from being inherently corrosion resistant, FRP rebar has high specific stiffness and strength, and is non-magnetic. The primary limiting factor of conventional FRP rebars is that they are linear elastic to failure, at low ultimate strains. As a result, higher safety factors must be used when designing structures reinforced with these materials, as they are unable to exhibit significant visual warning before ultimate failure. Improving the ductility of FRP rebar could allow for less conservative design practices to be used, resulting in material and cost savings. In this thesis, FRP rebar was developed to fail in a pseudoductile manner, meaning that ductility is achieved based on the composite architecture, rather than the inherent properties of its constituent fibers and matrix. The development process included rebar design, manufacturing, structural characterization, and mechanical testing. Pseudoductility was achieved by a combination of material and structural hybridization, with the final rebar consisting of a unidirectional carbon fiber core encased in a braided aramid fiber overwrap. The rebar used a thermosetting matrix material, and was manufactured by a dieless braidtrusion method, which combined aspects of pultrusion and braiding into a single continuous process. The rebar was characterized by various methods, including optical microscopy, scanning electron microscopy (SEM), and differential scanning calorimety (DSC), to determine constituent volume fractions, degree of cure, and rebar geometry, and also to assess manufacturing quality and consistency. Equations were presented that were successful in predicting braid angle and rebar dimensions based on manufacturing parameters. Tensile testing was conducted, which showed that the rebar design was successful in achieving the desired pseudoductile failure behavior. Analytical models were developed to predict the tensile behavior of the rebar, and were in good agreement with experimental findings. The models allowed the mechanical properties of the rebar to be predicted based on material properties and manufacturing parameters. An alternative method was presented to extend the pseudoductility of the FRP rebar by introducing discontinuities into the braided overwrap. The discontinuities were used to initiate pullout of the rebar prior to ultimate tensile failure, taking advantage of interfacial sliding between composite layers. Tensile testing was conducted on discontinuous rebar specimens to assess the viability of the proposed failure mechanism, and the design showed promise as a potential method for increased pseudoductility in FRP rebars.

• Subjects / Keywords

  • Braidtrusion
  • Composite
  • Rebar
  • Pseudoductile

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3PG1HT5N

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.