Category:503 Bridge Approach Slabs

A bridge approach slab is used to provide a smooth and structurally sound transition from the roadway pavement to the bridge. The area between the roadway embankment and the bridge frequently experiences differential settlement. This can be caused by a different degree of compaction than the roadway fill, or perhaps subsidence of compressible original soil layers under the weight of the new roadway fill while the bridge is founded on a more unyielding foundation of solid rock or piling. In order to mitigate possible settlement and excessive loading on the end bent, a 20 ft. long bridge approach slab is constructed to span/fill the area adjacent to both ends of abridge.

All new and replacement bridge construction shall include bridge approach slabs. Replacement of bridge approach slabs on redecking projects, while possible, is generally not required. Repair of existing bridge approach slabs on bridge rehabilitation projects, or adding approach slabs on bridge widening projects, or replacing bridge approach slabs generally will need to be determined by the project core team as necessary.

Standard details of bridge approach slabs are retained in the Bridge Standard Drawings. The appropriate bridge approach slab will be included on the bridge plan sheets prepared by the Bridge Division. The cost for bridge approach slabs is included in the bridge cost estimate. The concrete approach pavement shown on Standard Plan 504.00, which is the transition pavement between the bridge approach slab and the roadway pavement, is considered a roadway item and shall be included in the roadway cost estimate.

There are two primary classes of bridge approach slabs that follow from MoDOT roadway classification: the Bridge Approach Slab (Major Road) and the Bridge Approach Slab (Minor Road). The Bridge Approach Slab (Major Road) is a reinforced concrete slab. The Bridge Approach Slab (Minor Road) is a contractor-option slab consisting of two subclasses of slabs: either an optional lesser reinforced concrete slab, or an optional asphalt slab.

503.1 Major Roads

A reinforced concrete Bridge Approach Slab (Major Road), as well as the concrete approach pavement shown on Standard Plan 504.00, shall be used on all major roads. In site-specific circumstances, the project core team may decide a Bridge Approach Slab (Major Road), and concrete approach pavement, is excessive for the projected traffic volume or loading. In those cases, a design exception is required and the Minor Roads guidance in EPG 503.2 Minor Roads shall be followed.

503.2 Minor Roads

The Bridge Approach Slab (Minor Road) shall be used on all minor roads. If the project core team concludes that a concrete Bridge Approach Slab (Major Road) is needed on a minor road, perhaps due to heavy traffic volume, a design exception is required and the major roads guidance in EPG 503.1 Major Roads shall be followed.

The contractor will be given the option of constructing either subclass of slab in accordance with the bridge standard drawings. (Note: asphalt is considered a subclass slab since it is similarly associated with the first 20 ft. adjacent to the bridge ends where it is thickened, crowned and placed on a specifically prepared subgrade for improved drainage).

The concrete approach pavement shown on Standard Plan 504.00 is not to be used with the Bridge Approach Slab (Minor Road).

Bridge Approach Slab (Minor Road) Sub-Class Requirements

The Bridge Approach Slab (Minor) standard drawing will note the asphalt mix type required for the asphalt option. District Design is responsible for specifying the mix type, which will generally match the adjacent roadway design. The mix type should be noted on the Bridge Memorandum.

Guidance for Estimating Roadway Plans Quantities:

If asphalt is anticipated to be used for constructing the Bridge Approach Slab (Minor Road), and the approach slab asphalt is anticipated to be placed continuously with the adjacent roadway asphalt pavement, the asphalt tonnage for the roadway asphalt pavement will need to be computed for only the roadway pavement leading up to the final 20 ft. of roadway adjacent to the bridge ends. The asphalt tonnage used for the bridge approach slabs is included in the cost of the bridge approach slab pay item.

503.3 Bridge End Drainage

Bridge end drainage provisions should be considered on every bridge job.

Bridge end drainage provisions can include concrete spill slope protection, concrete slope aprons, drain basins, curbs, and sideslope drainage provisions which includes rock blanket or drain flumes, or a combination of these. (See EPG 748.7 Bridge Deck and Bridge End Drainage and Standard Plans 609.40 for details.)

503.4 Construction Inspection Guidance for Sec 503

Material and Construction Requirements. For material and construction requirements, refer to Sec 503 of the Standard Specifications.

A concrete bridge approach slab is not subject to the Quality Control/Quality Assurance (QC/QA) requirements of Sec 502 of the Standard Specifications. Concrete bridge approach slabs shall be cured and sealed in accordance with Sec 703 of the Standard Specifications for bridge decks.

Requirements for approach slabs constructed with asphalt will be in accordance with the either Sec 401 or Sec 403, as determined by the mix type to be specified on the plans.

When a Bridge Approach Slab (Minor Road) is constructed with asphalt, it is important to remember that the asphalt tonnage is included in the cost of the bridge approach slab pay item. If the asphalt slab is laid continuously with the adjacent roadway pavement, and the roadway asphalt pavement is paid per ton, the inspector will need to compute the quantity (tons) of asphalt that was needed to construct the 20 ft. approach slab and then deduct that amount from the total asphalt tonnage (i.e. ticket total) placed that day.

503.5 Maintenance Activities

See Mud Jacking Bridge Approach for additional information.