Superstructure Design Information - Corrosion Protection Measures

The permeability of HPC is significantly lower than that of ordinary concrete. Lower permeability concrete reduces the ability of chlorides to attack the reinforcing steel and cause corrosion.

The current statewide Special Provision to Item 421, Hydraulic Cement Concrete, covers the requirements for HPC.

Action:

The designer must indicate on the plans which elements require HPC. There are specific Bid Items for HPC.

• 1. Bridge Slabs & Rails - When indicated, specify Class "S" (HPC) for bridge slabs and Class “C” (HPC) for all concrete bridge railing elements.
  • This includes all cast-in-place superstructure concrete such as concrete slab & girder (Pan formed) spans, cast-in-place slab spans, box culverts that require Class “S” concrete in the top slab, as well as slabs cast on top of box beams, slab beams, or double tees.
  • When using HPC in the bridge slab, also specify HPC in the bridge approach slab if present.
  • HPC in the Prestressed Concrete Panels (PCP’s) used in bridge deck construction is not required.
• 2. Substructure - When indicated, specify Class "C" (HPC) for all substructure elements.
  • Applies to all abutments, bent caps and columns regardless of their locations relative to bridge expansion joints.
  • The use of HPC in piling, drilled shafts or buried footings is not recommended.
• 3. Prestressed concrete beams - The current statewide Special Provision to Item 424 requires concrete mixes that are effectively the same as HPC mixes in all precast concrete beams. Therefore, specifically requiring the use of HPC in precast concrete beams is not necessary.

Epoxy-coated reinforcement is a fusion-bonded coating on the reinforcing steel that provides protection from oxidation. Epoxy-coated reinforcement increases the time to initial corrosion as compared to uncoated reinforcement. It is not intended to protect exposed steel, as the coating is subject to degradation from ultraviolet light.

Item 440, Reinforcing Steel, covers the requirements for epoxy-coated reinforcement.

Action:

Provide notes on the bridge plan sheets to indicate which elements are to receive epoxy-coated reinforcement. In addition, specify epoxy-coated reinforcement in the General Notes to Item 440, Reinforcing Steel. Notes should indicate which bridge elements require epoxy-coated reinforcement. Do not specify partially epoxy coated bars. There is no direct payment for this work or materials.

• 1. Bridge Slabs & Rails - When indicated, specify epoxy-coated reinforcing for bridge slabs and concrete bridge railing elements.
  • Specify epoxy-coated reinforcing in both mats of steel in the bridge slab.
  • This includes cast-in-place slab spans, culverts that require Class “S” concrete in the top slab, as well as slabs cast on top of box beams, slab beams, or double tees.
  • For concrete slab & girder (Pan formed) spans, epoxy coat all superstructure reinforcing.
  • Specify epoxy-coated reinforcing in the bridge approach slab if present.
  • Prestressed Concrete Panels, PCP’s, used in bridge deck construction do not require epoxy coated reinforcement or epoxy coated prestressing strands.
  • By default, the bridge railing standard drawings require the use of epoxy-coated reinforcement in all concrete bridge railing elements when the bridge slab reinforcing is epoxy-coated. For bridges that do not have a cast-in-place bridge deck such as double tees, decked slab beams, or box beams, specify epoxy-coated reinforcing on the plans by providing notes in the General Notes to Item 440, Reinforcing Steel.
• 2. Substructure - When indicated, specify epoxy-coated reinforcement for all substructure elements.
  • Applies to all bent caps, and abutments regardless of their locations relative to bridge expansion joints. Note: Columns do not require epoxy-coated reinforcement.
  • The use of epoxy coated reinforcing bars for foundation elements (i.e. piling, drilled shafts or buried footings.) is not recommended.
• 3. Prestressed Concrete Beams - The use of epoxy coated reinforcing bars for prestressed concrete beams, except for bridge rail anchorage bars as indicated above, is not recommended. Do not epoxy coat the reinforcing bars that connect the bridge deck slab to the prestressed concrete beams even when the bridge deck slab reinforcing bars are epoxy coated. Specifically, do not epoxy coat R-bars (I-beams, I-girders and U-beams), Z-bars (box beams), H-bars (Slab beams), or C-bars (DT beams).
   

Increased clear cover to reinforcement beyond what is normally required places the reinforcement further away from the chlorides on the surface of the concrete and thereby reduces the potential for corrosion.

Action:

Clearly indicate increased clear cover requirements on the plans. There is no direct payment for this work.

• 1. Bridge Slabs - When increased clear cover for bridge slabs is indicated, modify bridge standard drawings as necessary to achieve additional top clear cover. See checklists for necessary standard drawing modifications.
  • For slabs on stringers (beams, girders or spread box beams), use 8.5 in. thick bridge slabs with 2.5 in. top clear cover. Use 8.5 in. as the structural thickness for design.
  • For slabs on adjacent beams (box beams, slab beams, or double tees), use 5 in. thick bridge slabs with 2.5 in. top clear cover.
  • For cast-in-place slab spans, use 2.5 in. top clear cover.
  • For Concrete Slab & Girder (Pan formed) bridges as well as culverts, do not specify additional top clear cover.
• 2. Substructure - Consider increased clear cover for substructure elements on a case-by-case basis at the discretion of the District.
  • Use primarily in areas of the state with a history of significant corrosion damage in substructure elements.
  • Specify an additional 0.5 in. of clear cover for bent caps, abutments and exposed footings.
  • Columns have sufficient clear cover.
  • Account for increased clear cover in the structural design.

Penetrating (Class II) Concrete Surface Treatments as provided under Item 428, can provide a short term (<10 yrs.) moisture barrier at the concrete surface.

• This can be an effective barrier to slow the migration of chlorides into the concrete.
• When used in conjunction with HPC, penetrating surface treatments may not be fully effective, since depth of penetration is restricted, but are still considered a reasonable corrosion protection measure, especially for concrete subject to early exposure to deicing agents.
• Item 428, Concrete surface Treatment, covers the requirements for Penetrating (Class II) Concrete Surface Treatment.

Action:

When concrete surface treatment is indicated, specify treatment of the upper surfaces of bridge slabs, bridge sidewalks and medians, the inside faces of curbs and concrete rails on the plans and in the General Notes to Item 428.
 

Air entrainment is achieved by providing concrete admixtures that deliberately entrain microscopic air bubbles. The presence of these air bubbles improves the freeze-thaw durability of the hardened concrete. In addition, they increase the resistance to surface scaling that can occur when deicing agents are used.

Freeze-thaw resistant concrete is not needed in most districts of the state. Good quality/low permeability concrete provides some freeze-thaw protection and is adequate for much of the state considering the low number of freeze-thaw events that occur per season. A freeze-thaw event requires moisture to be present for deterioration to occur.

The current Statewide Special Provision to Item 421, Hydraulic Cement Concrete, covers the requirements for air-entrainment.

Action:

By default, all structural concrete will receive air-entrainment. If air-entrainment is not desired, General Notes to Item 421 will be required to waive these requirements. Per the current Special Provision to Item 424, Precast Concrete Structures (Fabrication) air-entrained concrete is not required for precast concrete members.

Entrained Air General Notes for Item 421:
For AMA, CHS, LBB and WFS, no General Notes are required.

For ABL, ATL, BWD (Eastland and Stephens Counties), DAL, FTW, ODA (Andrews, Martin, Midland and Ector Counties), SJT (Coke, Concho, Glasscock, Irion, Reagan, Runnels, Sterling, and Tom Green Counties and Strs on IH 10): Entrained air is required in all bridge deck and slip formed concrete (bridge rail, concrete traffic barrier, pavement, etc.). Adjust the dosage of air entraining agent for low air contents as directed or allowed by the Engineer. If entrained air is provided where not required, only the upper limits of the Special Provision will be enforced.

For all other districts: Entrained air is required in all slip formed concrete (bridge rail, concrete traffic barrier, pavement, etc.), but is not required for other structural concrete. Adjust the dosage of air entraining agent for low air content as directed or allowed by the Engineer. If entrained air is provided where not required, only the upper limits of the Special Provision will be enforced.

Calcium-nitrite has been shown to delay the onset of corrosion. Calcium-nitrite is an approved concrete strength and set accelerator and has been used for prestressed concrete member fabrication.

It is not recommended for cast-in-place concrete because it can adversely affect workability. Other corrosion inhibiting admixtures have not consistently provided similar protection and are not recommended.

Action:

When the use of calcium-nitrite is indicated, provide notes on the bridge plan sheets indicating that the prestressed concrete beams are to receive calcium-nitrite. In addition, specify calcium-nitrite in the General Notes to Item 425.

Notes should indicate that the prestressed concrete beams are to receive calcium-nitrite at a dosage rate of 3 gal/CY. The use of calcium-nitrite in the prestressed concrete panels, PCP’s, used in bridge deck construction is not recommended. There is no direct payment for this work or materials.

ACP overlay tends to trap salt laden moisture and thereby accelerate corrosion.

Action:

Limit the use of ACP overlay on new bridge decks whenever possible. If an ACP overlay must be placed on a deck, always specify a two-course surface treatment be applied first. The two-course surface treatment serves as a membrane to help protect the bridge deck.
 

Open bridge rails allow deicing agents to run down the face of the outside beam.

Action:

Limit the use of open bridge rails. However, snow removal requirements may necessitate the use of open bridge rails.
 

Limiting the width of cracks in concrete reduces the ability for chlorides to penetrate to the reinforcing steel thereby reducing the potential for corrosion.

Action:

For structures where the use of HPC or epoxy coated reinforcing is indicated, design using Class 2 exposure condition to satisfy AASHTO LRFD 5.7.3.4, Control of Cracking by Distribution Reinforcement. See TxDOT Bridge Design Manual (LRFD) for further information.

This applies to abutment and bent caps only. It need not be applied to bridge slabs, beams or columns. The bridge standard drawings were developed using Class 2 exposure condition so no modifications to these drawings are required.
 

1. Epoxy waterproofing of bent caps, abutment caps, abutment backwalls, or columns.
2. Corrosion resistant reinforcement such as stainless steel, stainless-clad, MMFX, or fiber reinforced polymer (FRP).
3. Cathodic protection systems