Galvanized Reinforcing Steel
There are a number of benefits galvanized reinforcing steel provides. Steel is often used embedded in concrete which is porous; therefore it is important to protect it from corrosion. Many benefits help HDG rebars performance in concrete.
- Superior Corrosion Protection
- Design and Specification
Each of these benefits will be discussed in detail later on in the seminar.
Cost of Corrosion
The deterioration of reinforced concrete structures, such as bridges, is estimated to cost more than $20B annually. Increasing by nearly $500 million each year, spalling and concrete deterioration has become a major liability for highway agencies. There is, however, a way to protect these infrastructure investments from the ravages of corrosion. Using hot-dip galvanized steel rebar for corrosion protection in concrete bridge elements, such as decking, piers, or piles, ensures they will resist spalling and stand strong for generations.
Though steel is an excellent building material, as previously mentioned, when exposed to the atmosphere, corrosion will occur. Corrosion is a considerable concern as the annual costs are staggering (3% of the GDP in US/Canada) and $2.2T USD worldwide each year. However, the cost of corrosion is much greater than just financial, it can also lead to waste of natural resources, hazardous failures, and many other indirect costs. Corrosion is a natural phenomenon which can never be completely eliminated; however, it is a misconception nothing can be done. Employing adequate corrosion protection systems at the start of a project, such as hot-dip galvanizing, can significantly reduce these annual costs.
Addressing corrosion after construction is expensive and disruptive as all or part of the structure needs to be closed periodically for maintenance and repair. Failure to properly address corrosion can also lead to catastrophic structural failures with potentially deadly consequences. Many of these costs and safety issues are avoidable if the potential for corrosion is minimized during construction through proper design and material selection. This is especially critical for the reinforcing steel and the structural steel connectors used to strengthen and join concrete sections. Galvanizing, the process where steel parts are immersed in a bath of molten zinc, has a proven track record and should be your first choice in corrosion protection—because it works.
According to recent studies, the direct cost of metallic corrosion worldwide is $2.2T US dollars annually, while in the US it is estimated at approximately 3% of the GDP. The US GDP was $14.12T in 2009, leaving the corrosion price tag at $423B annually. However, this is only the direct cost of corrosion, there are also indirect costs to consider (losses to businesses, detours, etc), which can be up to 11 times greater than direct costs. By extending the life and durability of steel, not only will capital investments be less, but taxpayers' money will be spent more wisely. When you design and specify for corrosion protection, dont think only of initial costs, but also consider life-cycle costs.
Corrosion, if unchecked, contributes to waste, with dramatic environmental implications through process and plant failure. Further, the increased energy implications of replacing corroded structures are very significant in both financial and environmental terms. Specifiers must design and specify the longest product life possible. By doing this, your project will not need to be replaced or rehabilitated as frequently. Early project failures require unnecessary consumption of natural resources. By protecting steel against corrosion, resources such as iron ore and energy will be saved.
Corrosion control and public safety go hand-in-hand. For example, corrosion is one of the leading causes of bridge failure in the world. When a bridge fails, the results can be devastating in terms of loss of life, property damage, and environmental contamination. Spalling concrete can fall on those underneath the structure, creating an unsafe and hazardous area.
The public outcry and inconvenience is the verbalization of many indirect costs. For example, during the renovation of the Williamsburg Bridge, the New York City Department of Transportation had to completely close it to traffic for seven months due to its deteriorated condition. Inspections at that time found 30 areas of major corrosion in the structure. At first, it was decided to entirely replace the debilitated bridge, but building a new bridge in a different location would negatively impact businesses located near the Williamsburg Bridge. Replacing the bridge would have caused this main artery for vehicles to be closed for many more months. Already, the seven-month closure caused public infuriation.
HDG Rebar Case Study
Stoneham Arch Bridge- Stoneham, Quebec, 2012
This suspended arch bridge is an aesthetically pleasing solution to a unique site requirement. The choice of hot-dip galvanizing was preferred by the engineer because of its durability and cost compared to weathering steel in this highly corrosive environment. The resulting bridge is a beautiful and cost-effective marriage between structural steel and reinforced concrete.
The arched bridge design, unusual for a highway overpass, was chosen primarily to overcome two problems; uneven and rocky field conditions, as well as the very obtuse angle at which the road passed over the highway, which did not fit well with typical overpass construction. Steel beams were chosen for the deck because of the lower weight as compared to concrete. These beams were also designed to be galvanized rather than metallized, again, for economic and performance reasons. As for the reinforcing steel, the choice of hot dip galvanizing was obvious since the concrete arches needed to be protected both structurally and aesthetically.
This type of bridge design, combining steel and concrete, is not often used. The unique design of this type of bridge makes it very interesting both architecturally and structurally. The use of galvanizing in all aspects of the bridge breaks new ground for our industry. Galvanized structural steel, galvanized reinforcing steel in the concrete, and even the supporting cables are galvanized (cables were supplied galvanized by the cable manufacturer).
The province of Quebec has a long history of being a leader in the use of galvanizing, going back to fully-galvanized road bridges from the early 1960s and galvanized reinforcing steel since the 1990s in road structures. The new ministry standards for an expected 75-year lifespan further drove the need for galvanizing in road infrastructure.