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Marine Structures

Marine structures are often exposed to highly corrosive environments, making them ideal for the use of ChromX® rebar.

Different areas of the same marine structure have different corrosion protection requirements. The full ChromX® product line (9100, 4100, 2100) allows designers and engineers to select the product that best fits the application. A pier is shown as an example below.


Pier rendering showing applications of ChromX in different zones.

 

Atmospheric Zone. A marine atmosphere is very corrosive due to chloride exposure from salt spray, salt fog and salt mist. For atmospheric pier members in marine environments designer should consider using ChromX® 4100 or 9100 depending on the target service life for the structure.

Splash and Tidal Zones. The splash and tidal zones are generally severe corrosive environments due to repeated wet and dry saltwater exposure, requiring ChromX® 9100's corrosion protection.

Submerged Zone. While actually less corrosive than the splash zone, designers should still consider ChromX® 9100 or 4100 for the submerged zone.

Embedded Zone. There is usually lower corrosion potential in the embedded zone depending on the composition and contents of the soil, therefore ChromX® 2100 may be the right choice.

The marine structure's service life (the time to first repair) is driven by the corrosion on the reinforcing steel. Reinforcing steel corrosion begins when the chloride concentration at the steel surface reaches the critical chloride threshold (CT) value of that steel. The corrosion continues at the corrosion rate (CR) of the steel, eventually causing cracking and spalling of the concrete and deterioration of the structure.

The CT of ChromX® 9100 is four times that of black bar and twice that of ChromX® 4100. In addition, both ChromX® 9100 and 4100 have a CR value of one-third that of black bar. These higher CT and lower CR values are the reason the ChromX® products extend the structure's service life, saving repair and maintenance costs, resulting in life-cycle costs compared to other steel reinforcing products.

 

Cost Comparison Using High Strength, Corrosion Resistant Rebar

To illustrate the value potential of ChromX® 9100 rebar with both its corrosion resistance and high strength properties, below are details on a Dubai, UAE diaphragm wall that was redesigned to Grade 600 MPa versus Grade 460 MPa design. U.S cost factors of materials and labor were used for this comparison.

By designing this seawall with ChromX® 9100 Grade 600 rebar, the designers were able to:

  • Save approximately 2% of upfront construction costs (using ChromX® 9100 over epoxy-coated rebar) 
  • Reduce construction time by 20%
  • Reduce the thickness of the wall by 10%, saving valuable real estate along the canal
  • Lower life cycle costs over a 100-year service life by an estimated 26% for a total savings of over $27 million

In addition, ChromX® 9100 rebar provides over 100 years of service life in concrete compared to only 34 years estimated for epoxy-coated rebar.

The savings in repair costs are realized upon the initial repair of the epoxy-coated rebar structure, which is estimated to be within 34 years of construction. These initial repair costs alone are estimated at a net present value of $9.7 million.

Combined with the estimated upfront construction cost savings from the high strength design, the total savings realized from using ChromX® 9100 form rebar is approximately $11 million within the first 34 years, with many more subsequent repairs scheduled for the epoxy-coated rebar structure.


The table below provides a comparison of ChromX® 9100 rebar to epoxy-coated rebar (ECR) using a specific redesigned seawall as an example.

 

High Strength Steel & Corrosion Resistant Rebar Seawall Design Comparison Table
Seawall Example - Metric
8/27/2015
Grade 460
ECR

Grade 600
ChromX® 9100

Added Cost /
Savings
%
Construction Cost
Rebar Quantities (metric tons)
Steel Related Costs
Concrete Costs
Other Construction Expenses: Excavation
Total Construction Cost =
 
20,000
$37,100,000
$37,970,323
$3,043,591
$78,113,914
 
15,333
$39,943,333
$34,173,290
$2,739,232
$76,855,856
 
(4,667)
$2,843,333
($3,797,032)
($304,359)
($1,258,058)
 
-23%
8%
-10%
-10%
-2%
Other VE Considerations
Number of Trucks
Construction Time (in hours)
Construction Time Savings =

22,2448
2,924

20,107
2,338

(2,342)
(586)



-20%
Service Life & LCCA
Service Life
NPV of Repairs
Total Life Cycle Costs
Life Cycle Cost Analysis Savings =
 
34
$25,911,409
$104,025,323

101
$0
$76,855,856

67
($25,911,409)
($27,169,467)




-26%
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