Design and Detailing of Cast-in-Place and Precast Concrete Approach Slabs

Background The approach slab is a structural concrete slab designed to span from the back wall of the abutment (i.e. end of the bridge floor) to the grade beam or sleeper slab where the paving section begins. The purpose of the approach slab is to carry the dead and live loads over the backfill behind the abutments to avoid possible settlement of the backfill. Despite the simplicity of approach slab design as one-way reinforced concrete slab, it has been reported that most approach slabs experience cracking at early ages, as shown in Figure 1, which results in premature deterioration and shorter service life. The causes of this cracking are not clearly understood. On the other hand, NDOT recently considered the use of precast concrete approach slabs to achieve higher quality and faster construction than cast-in-place (CIP) concrete approach slabs. The first implementation of precast concrete approach slabs was completed in the summer of 2018 in the construction of Belden-Laurel Bridge. Several lessons were learned from this project, which could be considered to improve the design, fabrication, and construction of precast concrete approach slabs. Therefore, it is important and timely to re-visit the current design, detailing, and construction practice of standard CIP and precast concrete approach slabs in order to improve their durability and speed of construction. Objective The objective of this study is twofold: 1) investigate the causes of cracking of standard CIP concrete approach slabs and propose a refined design, detailing, and construction procedure; and 2) propose design alternatives using precast concrete approach slabs based on the experience gained from the recent implementation . Special attention will be given to the longitudinal joints between the approach slabs, transverse joints with the paving section and end of floor. The new design alternatives could benefit from the recent development in the use of advanced materials, such as ultra-high performance concrete and glass fiber reinforced polymer (GFRP) reinforcement to enhance durability and speed of construction.

    Language

    • English

    Project

    • Status: Active
    • Funding: $ $78,648.00
    • Sponsor Organizations:

      Nebraska Department of Transportation

      1500 Nebraska 2
      Lincoln, Nebraska  United States  68502
    • Project Managers:

      Halsey, Lieska

    • Performing Organizations:

      University of Nebraska, Lincoln

      1400 R Street
      Lincoln, NE  United States  68588
    • Principal Investigators:

      Morcous, George

    • Start Date: 20190701
    • Expected Completion Date: 20201231
    • Actual Completion Date: 0
    • USDOT Program: Transportation, Planning, Research, and Development

    Subject/Index Terms

    Filing Info

    • Accession Number: 01705861
    • Record Type: Research project
    • Source Agency: Nebraska Department of Transportation
    • Files: RiP, STATEDOT
    • Created Date: May 24 2019 12:16PM