Marine structures, such as seawalls, submarine tunnels, piers, and groins, are engineering facilities which are constructed as a source of development and marine resource exploitation. Rock, sand, concrete, and steel are some of the conventional materials used in marine applications. Marine concrete structures have to withstand the extreme environmental pressure. They are subject to corrosive agents which can corrode the reinforcing steel causing spalling, rusting, and shortening the service life of the structure.
Corrosion and marine environment
Corrosion can simply be described as the deterioration of a metal by an electrochemical reaction. The pH of the concrete can fall when it became carbonated, causing the loss of passivity. The passivation layer is broken when chlorides reach the steel. Some of the common causes of corrosion are:
- Chloride-containing admixtures
- Sea water
- Airborne chlorides
- Carbon dioxide in the atmosphere
- Sea dredged aggregates
Corrosion process forms rust, causing a seven times increase in the volume of reinforcement bars. The dramatic change in volume causes spalling of the concrete surface making it even more vulnerable to aggressive environment. The abundance of moisture and chlorides make the environment extremely harsh for marine construction projects. Some of the structure that are build in or close proximity to oceans are:
- Retaining walls, seawalls
- Floating structures
- Decks, quays, and piles
- Boat ramps, jetties, and bulkheads
- Roads, buildings, and aquariums
How to control corrosion
So far as marine structures are concerned, reinforcement concrete needs to be a highly durable and corrosion-free structural material demanding little or no maintenance. Without correct mixing, design, placement, and curing, the durability of concrete can be impaired. Good practices and quality material can play a role in minimizing the direct maintenance cost and increasing the life cycle of a sensitive concrete structure.
Glass fiber reinforced polymer (GFRP) reinforcement has compelling mechanical and physical properties that make GFRP particularly attractive for marine structures operating in aggressive environments such as coastal regions, public infrastructure, and buildings that host sensitive equipment. The property of being corrosion-free makes fiberglass rebar a perfect alternative to conventional steel bars which cannot resist rust. Pultrusion is the manufacturing process used to produce fiber reinforced polymer (FRP) bars.
Marine structures reinforced with fiberglass rebar are invulnerable to strong chlorides and moisture. When bonded in concrete, GFRP or fiberglass bars do not react to chemical products, salt, and alkali. Fiberglass rebar is not manufactured with steel or any other metal the pultrusion process helps produce fiberglass rebar that is twice the tensile strength of steel bars. Furthermore, GFRP bars do not interfere with the sensitive electronic equipment.