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Validating the Durability of Corrosion Resistant Mineral Admixture Concrete (04-GS108)

Project #: 4W1495
Start Date: 06/30/2006
End Date: 06/30/2010
ABSTRACT:

As our country’s growth and development spurs the expansion of the nation’s highway system, each year hundreds of miles of public roads and highways are built, widened, realigned, patched, modified or reconstructed. As concrete is the most widely used manmade material on earth, the concrete industry has great potential for recycled materials.  Recent years have seen increasing interest in Environmentally-Friendly Concretes (EFCs), which utilize alternative or recycled materials and thus benefit the environment. Among them, mineral admixtures such as fly ash, silica fume, and slag – have been used to replace cement in concrete while shown to enhance concrete durability and improve resistance to chloride diffusion.

 

Caltrans has developed concrete mixes for corrosion mitigation of structures to meet AASHTO Load and Resistance Factor Design (LRFD) Bridge Specification requirement of a 75-year design life. However, the work to date has been based on diffusion coefficient data for low permeability, mineral admixture concretes selected from available literature, which may not represent the materials and exposure conditions seen in California. Additional research is thus needed to validate the corrosion mitigation design assumptions by Caltrans. There is also a significant amount of variability in determining chloride diffusion coefficients as an indicator of concrete durability, and existing chloride permeability tests are either very time-consuming for high quality concrete mixes or too biased to provide reliable chloride diffusion coefficients. WTI will establish a modified Rapid Chloride Permeability Test (RCPT) to simultaneously determine the chloride diffusion coefficient and chloride depassivation thresholds in concrete mixes.  This electrically accelerated method will force the penetration of chlorides into concrete and thus significantly reduces the time to initiate corrosion of rebar in steel. As such, this accelerated test will provide valuable information about the durability of the reinforced concrete, especially those with mineral admixtures, in a quick and reliable fashion.

Appropriate design for corrosion protection may generate substantial cost savings. The accelerated test method could be used for developing performance-based specifications for these types of concrete mix designs and for evaluating environmentally friendly concrete mix designs that could help reduce greenhouse emissions from the production of cement.

OBJECTIVE:

The purpose of this project was to assist Caltrans by validating chloride diffusion coefficients of mineral admixture concrete mix designs currently specified for corrosion mitigation. Furthermore, WTI will establish an accelerated test method to evaluate the chloride permeability of concrete mix design containing mineral admixtures.

PERSONNEL:

  • Xianming Shi
    (PI)
    Xianming Shi
    (PI)
  • Bret Gunnick
    (Co-PI)
    Bret Gunnick
    (Co-PI)

REPORTS & DOCUMENTS:

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