THE CONCRETE BRIDGE MAGAZINE

Summer 2019

ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

Issue link: http://www.aspiremagazinebyengineers.com/i/1134112

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F O C U S F O C U S The field of concrete petrography, the microscopic study of concrete's composition and the related quality and durability issues, has grown in significance for the design, construction, and maintenance of concrete bridges. Concrete petrographers analyze new and existing concrete infrastructure to provide information that engineers c a n u s e t o f o r m u l a t e re p a i r a n d maintenance options to extend the service life of structures. DRP, a Twining Company based in Boulder, Colo., has been at the forefront of advances in concrete petrography. "Bridge owners have limited funds to address an overall aging infrastructure, and they must fully understand the condition of the materials in their bridges to know how best to address repairs," explains David Rothstein, DRP's president and founder. "Advanced expertise is required to understand what investigative methods will work most effectively to get engineers the information they need to repair or rehabilitate a structure," he states. "The only thing worse than not repairing a weakened bridge is to spend time and money on a repair without recognizing the real problem and having the repair fail." 'The only thing worse than not repairing a weakened bridge is to spend time and money on a repair without recognizing the real problem and having the repair fail.' Rothstein began his consulting work in 1996 and has seen the field become more analytical, precise, and valuable (for more on DRP's history, see the sidebar to this article). "Our strength is that we take a very close look at a small part of the elephant to help owners and engineers understand what is really happening," he says. "We understand we're one piece in the bigger picture— but it's an important piece." Quantifying Observations DRP's goal is to quantify evaluative observations with more precision. "The trend is definitely toward providing more quantitative measurements," says Rothstein. "A lot of work in this field has been based on descriptions, and engineers are not wild about descriptions. They prefer numbers." A recent innovation is fluorescence microscopy, which the firm has been a c t i v e l y u s i n g s i n c e 2 0 1 8 . D R P 's concrete petrographers are now able to use thin sections containing epoxy with fluorescent dye to view the cement paste's microstructure. This technique produces objective measurements of the capillary porosity of the paste, which generally shows a strong correlation w i t h w a t e r- t o - c e m e n t r a t i o . T h e brightness of the green fluorescent tone in an area is proportional to the amount of epoxy infiltrating the material. A void (essentially 100% porosity) will be bright green, and a dense aggregate such as quartz (0% porosity) will be black. "There was a learning curve with the equipment; it's not just a plug-and- play system," Rothstein says. "We Concrete Micromanagement DRP, a Twining Company, employs a growing array of high-tech instruments and advanced analytics to help extend the service lives of bridges. by Craig A. Shutt A concrete slab polished and impregnated with fluorescent epoxy and photographed under ultraviolet light. The bright-green areas show cracks and voids; the cracking is due to a combination of alkali-silica reaction and freezing-and-thawing damage. All Figures and Photos: DRP, a Twining Company. 6 | ASPIRE Summer 2019

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