Composite Rebar

Introduction

The greatest weakness of concrete is its low tensile strength which has been remedied by using steel rebar on the tension side of the concrete. However, a major and unavoidable disadvantage of steel rebar is its susceptibility to corrosion.

Having a concrete cover that’s too thin allows water to penetrate and react with steel rebar causing the concrete to crack. Occasionally concrete aggregates react with the steel causing the concrete to spall and rust.

If steel rebar rusts it will reduce the strength of the reinforced concrete. When rust forms around steel rebar, the internal pressure will significantly increase around the surrounding concrete, leading to crack propagation.

When steel bars corrode, deterioration of the structure will be quite rapid and dramatic.

Other disadvantages of steel rebar are its high weight and conductivity.

Composite Rebar

Figure 1: Steel rebar [Google]

CFRP rebar has been applied in concrete structures as a superior alternative to conventional steel reinforcement since it offers significant advantages over steel reinforcement, for example, it is a long-term solution to steel reinforcement corrosion.

Composite Rebar

Figure 2: CFRP rebar components

Why use CFRP rebar? 

  • Extend the service life and durability of a concrete structure
  • Tensile strength is 1.5~2 times higher than steel rebar
  • Significant elongation
  • Electrically and thermally non-conductive (good choice for MRI medical equipment)
  • Impervious to chloride ions and chemical attacks
  • Non-corrosive and rust-resistant making it the perfect solution against deicing salts and marine salts in aggressively corrosive environments
  • Less concrete cover is required
  • Reduce maintenance costs
  • Lightweight: its weight is about 1/4th of common steel rebar so application and transportation are much easier and quicker
  • Higher strength-to-weight ratio: this specification will increase the load bearing capacity of the structure and will reduce the whole weight of the structure which results in a reduction of earthquake forces
  • Improve mechanical and fatigue behavior of the concrete structure which makes it suitable for cyclic loading situations like roads and bridges
  • It is a user-friendly product as it can easily be cut and there is no need for any special equipment
  • Higher stiffness of CFRP rebar leads to decreasing the required length of rebar in concrete ¹
Composite Rebar

Figure 3: CFRP rebar [Google]

CFRP rebar applications:

  • The corrosion resistance of CFRP rebar makes it an excellent solution for chemical and waste-water treatment plants, sea walls, floating docks, underwater structures, bridge decks, airport runways, pre-cast concrete, pavement which is treated with deicing salts, etc.
  • CFRP rebar is dielectric so it is being used around high electric and magnetic fields like substation reactor bases, airport runways, hospitals, laboratories, MRI medical equipment or other electromagnetic-sensitive equipment.
  • When reinforcing concrete with CFRP rebar, considering adequate anchorage of the bars is of high importance. The bond between CFRP rebar and concrete, without proper anchorage, is 2/3rd of the bond strength of steel rebar and concrete. ²
  • CFRP rebar is an effective choice for stirrups and spiral hoops as it increases strength, toughness and ductility of the concrete core in columns, and it can efficiently eliminate longitudinal bar buckling. ³
  • When the environmental impact of steel and CFRP reinforced pavement were compared, the following results emerged:
  1. By using CFRP bars, the overall thickness of the section will be reduced due to the concrete cover reduction; the cement content will be reduced as well.
  2. By using CFRP in place of steel rebar in concrete pavement, the environmental load will be reduced by 50%. This reduction is mainly due to a decrease in required maintenance activities of steel reinforcement (36%), and a reduction of the environmental load of pavement erection (15~22%). ⁴

Authors

Parastoo Azad and Dr. Mehrtash Soltani (May 12, 2021)

References

  1. American Concrete Institute. (ACI) (2015). “Guide for the design and construction of structural concrete reinforced with FRP bars.” 440.1R-15.
  2. Bartholomew, V. L. (1993). FRP Reinforcing Bars in Reinforced Concrete Members. ACI MATERIALS JOURNAL.
  3. Hany Tobbi, A. S. (2012). Concrete Columns Reinforced Longitudinally and Transversally with Glass Fiber-Reinforced Polymer Bars. ACI STRUCTURAL JOURNAL.
  4. Katz, A. (2004). Environmental Impact of Steel and Fiber–Reinforced Polymer Reinforced Pavements. Journal of Composites for Construction, 481-488.