ChromX® extends the operational service life of bridges and highway paving.
ChromX® provides high strength with varying levels of corrosion resistance, so designers can utilize the high strength efficiencies and best match the corrosion protection requirements of the structure.
All ChromX® rebar has substantially higher chloride threshold value (CT) levels than black bar. For example, ChromX 9100®’s CT value is four times that of black bar and twice that of galvanized bar. In addition, the corrosion rate (CR) value for ChromX® rebar is one-third that of black bar. These higher CT and lower CR values are the reason that ChromX® products extend the structure’s service life, saving repair and maintenance costs, resulting in lower life-cycle costs compared to other steel reinforcing products.
A bridge's service life (the amount of time from project completion to the first repair) is driven by the corrosion of the reinforcing steel inside the concrete. Reinforcing steel corrosion begins when the chloride concentration at the steel surface reaches the critical chloride threshold value of that steel. The corrosion continues at the corrosion rate of the steel, eventually causing cracking and spalling of the concrete and deterioration of the structure.
Below is a comparison of service life and life cycle cost analysis (LCCA) in bridge decks.
||Est. Initial Cost
|ChromX® 4100 w/CNI4
|Stainless Steel (UNS S32304)
1. Service lives estimated based on CT values determined in Critical Chloride Corrosion Threshold for Galvanized Reinforcing Bars, David Darwin et al., Univ. of Kansas Center for Research, Inc. (Dec. 2007), as well as CT and CR values, and STADIUM® software modeling for a concrete bridge deck with 1.5 in. (37.5 mm) Bridge Mix LP concrete cover according to Reinforcing Steel Comparative Durability Assessment and 100 Year Service Life, Tourney Consulting Group, LLC (June 2016).
2. Estimated net present value (NPV) per square foot of the total life cycle costs of the bridge deck, assuming $150 per square foot repair costs every 15 years after year of initial repair.
3. Based on chloride threshold data from Tourney Consulting Group, LLC testing of ChromX® 2100 Alloy (2017).
4. Adding 2 gallons of calcium nitrite (CNI) as a concrete additive at an estimated cost of $12 per cubic yard has been shown to further enhance ChromX® 4100's corrosion performance.
Designing with ChromX® protects all sensitive zones both above and below the structure. Each ChromX® rebar series can be used in different areas of a bridge, depending on the corrosion resistance required for that particular portion of the structure.
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Atmospheric Zone. The atmosphere to which the bridge is exposed varies widely with the location of the bridge. Inland bridge atmosphere is relatively benign and therefore raises low to no corrosion concern, while bridges over or near seawater have higher corrosion potential. Atmospheric bridge members for inland bridges can use ChromX® 2100, while bridges exposed to seawater will use ChromX® 4100 or 9100.
Deck and De-icing Salt Spray Zone. ChromX® 9100 should be used in the areas of a bridge where de-icing salts are used.
Splash Zone. The splash zone is a severe corrosive environment requiring ChromX® 9100’s high corrosion protection.
Submerged Zone. Designers should consider ChromX® 9100 or 4100 for the submerged zone, which is less corrosive than the splash zone.
Embedded Zone. There is usually low corrosion potential in the embedded zone depending on the composition and contents of the soil, therefore ChromX® 2100 is the optimum choice.
Designing with ChromX® saves funds over the life of any structure. Below shows the significant savings that are realized upon the first repair and accumulate throughout the service life.
There are advantages of designing with ChromX® for a variety of bridge components, including:
Decks: ChromX® fortification against corrosion will provide longer lasting vehicular load support and assist in distributing these loads more effectively to the steel superstructure.
Girders: High strength ChromX® bar will provide more overall strength, deck support and corrosion resistance at all vulnerability zones.
Piles/Columns: Using ChromX® to support a substructure footing (either above or below ground) ensures a longer life, higher corrosion resistance and a safer compression/tension ratio.
Abutments: The material that comprises the location of a superstructure contact is critical to a bridge's ultimate stability. ChromX® not only provides the strength and corrosion resistance, but also includes an additional level of protection due to its intrinsic properties.
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