High Performance Concrete in Colorado

This article reviews the technology advances and performance requirements that continue to raise the bar for high performance concrete. The author describes the Colorado Department of Transportation's (CDOT) activities using higher performance concrete (HPC) in bridge decks that use Class H and HT concretes. These concretes are used for bridge decks that do not receive a waterproofing membrane. The author describes specific challenges including how to achieve lower permeabilities and less cracking in bridge decks or higher compressive strengths for girders. Lower permeability was obtained with the addition of fly ash and silica fume and lower cement content. The lower permeability helps slow the ingress of moisture and chlorides thus protecting the reinforcing steel. The lower cement content helps reduce shrinkage cracking. The addition of fly ash and silica fume also provided higher strength to offset the lower cement content. The author concludes with a section of lessons learned, focusing on the idea that no matter how high performance a concrete may be, the use of poor construction practices will result in poorly performing concrete. The use of HPC must be teamed with proper design and construction practices. Readers are referred to the website for CDOT Standard Specifications for Roads and Bridge Construction (http://www.dot.state.co.us/DesignSupport/Construction/2005SpecsBook/2005Book/sec601.pdf).