February 24, 2018 By V. Lidya
Steel reinforcing bars have long been used as a building material for its high tensile strength and durability. However, it has one weakness; susceptibility to corrosion (oxidation) when exposed to water and chemicals that enter into the concrete. As the steel rebar corrodes, it makes the concrete to crack and break, thus leading to openings which initiates further and faster deterioration of steel and concrete.
Many chemicals and coatings have been introduced over the years to help keep out moisture from entering concrete. Epoxy coatings are sometimes applied on TMT rebars to prevent corrosion. Manufacturers also sell Corrosion Resistant Steel (CRS) that have a better ability to withstand corrosion.
Another weakness of steel rebars is that they are vulnerable to electrical and magnetic fields, which makes reinforced concrete undesirable for certain applications.
Glass Fiber Reinforced Polymer (GFRP) bars or Fiberglass Rebars
Glass Fiber Reinforced Polymer (GFRP) bars or Fiberglass rebars have been developed as an alternative to steel reinforcement for various structural concrete applications. Due to their non-corrosive nature, they are particularly suited for harsh environments (like underwater) where steel reinforcement is prone to corrosion. GFRP is popular not only for its non-corrosive property but also for its light weight, non-magnetic and high strength properties.
How Is It Manufactured?
GFRP bars are manufactured by Pultrusion process which is much simpler than steel rebar production. In Pultrusion process, the fibers are initially treated at 160 degrees Celsius in mould and rod is constantly pulled out from mould through a device which coats them with polymer resin. These rods are then kept under 140 degrees Celsius for post-curing process and finally cut to length.
Why GFRP rebars and not Steel?
GFRP rebar has overcome some of the limitations of steel.
- One-fourth the weight of steel rebars.
- Superior tensile strength than steel rebars.
- Lower stiffness compared to steel (allows structures to be less rigid).
- Lower thermal expansion.
- Non-conductive to electrical and magnetic fields.
- 100% corrosion resistance, as well as to alkali and acidic environment.
- Virtually maintenance free.
Designing Structures Using GFRP Reinforcement
Since the mechanical properties of GFRP fiberglass rebar differ from those of steel, it is necessary to consider the following points before designing your concrete structures using fiberglass rebar:
- Direct substitution of GFRP fiberglass rebar with steel rebar may not be possible in some cases.
- A lower modulus of elasticity and shear strength impact the number of reinforcing bars required.
- GFRP fiberglass rebar has a limited maximum sustained shear stress.
- Some types of GFRP fiberglass rebar are not suitable for certain pre-stressing or post-tensioning applications.
Where can GFRP Rebars Be Used?
It can be used in many applications where concrete is exposed to harsh environment with exposure to water and salts like chlorides. It can also be used where electro-magnetic fields rule out the use of steel reinforcement.
- Marine Structures
- Precast Structures
- High Voltage and Radio Frequency Sensitive Areas, Etc.
Fiberglass rebars cannot be bent on site. The bending process needs to be done before the curing process of the thermosetting resin. Due to this, better planning is required by the contractor. The rebar bending schedule needs to be made in advance and sent to the supplier for manufacturing. An advantage is that there is no need for cutting and bending activity on site, freeing up space and reducing labour requirement on site.
Fiberglass reinforcement is relatively expensive compared to traditional steel reinforcement is relatively inexpensive. However, considering lifetime costs, fiberglass rebars are a cost-effective building material as they give a concrete structure long lifespan of over 100 years without major maintenance. The technology is proven in the field, many structures have been built showcasing the potential for GFRP reinforcement to be used in various applications.
We hope that this technology will gain awareness and will evolve in India as a successful project.