Performance Blend: Supplementary Materials Can Extend Concrete Life and Produce Longer-Lasting Bridges

This article describes current trends in the use of optimized concrete mixes using supplementary cementitious materials (SCMs). One noteworthy project is the Confederation Bridge, which crosses the North Atlantic Ocean in Canada, connecting Prince Edward Island with New Brunswick. It stretches eight miles and is exposed to some of the world’s harshest weather, including high wind, salty waves, and ice. It was built with seven different concrete mix designs incorporating SCMs. The SCMs included silica fume and fly ash. They were used to achieve low permeability, high strength, low heat rise, and resistance to freezing and thawing. SCMs can be used either as separate components or as a constituent of a blended cement. Binary blends contain portland cement and one SCM; ternary blends contain portland cement and two SCMs; and quaternary blends have three SCMs. Fly ash, slag cement, and silica fume are generally the most commonly used SCMs. The spherical shape of fly-ash particles and the glassy nature of slag-cement particles reduce the amount of water needed to make a workable concrete. Silica fume can have an adverse effect on workability. Slag cements, which are generally finer than portland cement, can reduce bleed water. Their use, along with the use of fly ash, will lower early strengths (one to 14 days) but add significantly to long-term strength (28 days and beyond). Concrete with SCMs generally resists sulfate attack more successfully and prevents excessive expansion and cracking of concrete due to alkali-silica reaction. Considering that the three SCMs are industrial byproducts that are difficult to dispose of, their use in creating new pavement is a welcome step toward increased sustainability. Three other examples of projects using optimized SCM mixes are also briefly described.

Language

  • English

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Filing Info

  • Accession Number: 01120190
  • Record Type: Publication
  • Source Agency: UC Berkeley Transportation Library
  • Files: BTRIS, TRIS, ATRI
  • Created Date: Jan 22 2009 6:27PM