WTI

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

Primary Investigator Contact Information

External Project Contact(s)

Report(s)

There are no reports associated with this project.

Project Objective

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.

Project 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 reduce 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.

Task Descriptions

1. Experimental Design
   1. WTI will design and evaluate experiments in the form of a matrix of 18 concrete mix designs. The concrete mix design without mineral admixtures will be used as a control.
2. Literature Review
   1. A comprehensive literature review to further investigate corrosion mechanisms of concrete embedded steel rebar, methods of determining chloride diffusion coefficients of concrete, modeling of chloride ion ingress in concrete, and assessment of concrete durability.
3. Project Management
   1. This task will involve regular communications between WTI and Caltrans including a kick-off meeting, quarterly progress reports and a final report.
4. Service Life Modeling
   1. Using the results from the Laboratory Investigation, the chloride concentration will be plotted against depth in the concrete in terms of millimeters.
5. Experimental Setup for Rapid Chloride Permeability Tests (RCPT)
   1. Researchers will establish and utilize a modified RCPT that is both rapid and informative. The modified test will measure the chloride concentration profile after the accelerated chloride migration into the concrete sample. The new method will enable the simultaneous determination of the apparent chloride diffusion coefficient and the threshold concentration.
6. Laboratory Investigation
   1. Researchers will fabricate and cure reinforced concrete slabs according to rigorous standards and subject them to the Rapid Chloride Permeability Test.

Milestones, Dates, Schedule

Student Involvement

True

Relationship to Other Research Projects

True

Technology Transfer Activities

False

Transportation Research Board Keywords

Concrete, corrosion, steel

Partners

Corrosion Technology Branch, California Department of Transportation