It's All in the Mix

Corrosion is a common factor in the need to repair concrete bridge decks. This article discusses why corrosion occurs and what can be done to eliminate cracking. It also describes some products that can make improve the impermeability of concrete. Corrosion begins when chlorides from deicing solutions enter the reinforced concrete through cracks and water channels and reach the reinforcing steel, destroying its protective film. Since the products of corrosion occupy a greater volume than the constituents, an internal pressure develops, leading to cracking and spalling of the concrete cover above the steel. This in turn reduces the bond and anchorage of the steel to the concrete, deleteriously affecting the structural properties of the deck. The most common cause of cracking is drying shrinkage, which results in tensile stresses at a time when the concrete has little or no tensile strength. Shrinkage-compensating cement combines an expansive component with portland cement to offset the tensile stresses caused by shrinkage. Concrete containing this cement is virtually crack-free and does not bleed, hence there are no water channels to the surface. No cracks plus no water channels equals low chloride permeability and longer life. For new or replacement bridge decks, shrinkage-compensated concrete is an excellent choice. However, not all damaged decks need to be replaced. The damaged areas often can be repaired and an overlay placed on the deck to restore riding quality. Latex-modified concrete (LMC) overlays are relatively impermeable but require a number of days to gain sufficient strength so that they can be opened to traffic. A more efficient alternative called LMC-VE (for Very Early) concrete exists that can dramatically accelerate repairs and has proven to be durable over a period of 10 years.

Language

  • English

Media Info

  • Media Type: Print
  • Features: Photos;
  • Pagination: pp 8-10
  • Serial:
    • Bridges
    • Volume: 10
    • Issue Number: 6
    • Publisher: ZweigWhite

Subject/Index Terms

Filing Info

  • Accession Number: 01100297
  • Record Type: Publication
  • Files: TRIS
  • Created Date: May 29 2008 11:13PM