United States Department of Transportation
i
Detecting Deleterious Fine Particles in Concrete Aggregates and Defining Their Impact [Research Brief]
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2011-02-01
[PDF-786.22 KB]
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OCLC Number:747967457
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Edition:Research brief.
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Materials;NTL-HIGHWAY/ROAD TRANSPORTATION-Construction and Maintenance;
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Abstract:As concrete hardens, it develops mechanical properties such as strength and stiffness that depend in part on the ratios of the water, cement paste and aggregate gravel that compose it. While enough water must be added to concrete so it can be mixed, placed, compacted and molded during construction, too much water will lead to a weaker final product. This balance is further affected by aggregates that are typically coated with a dust of microfines, or small particles composed of various minerals. This dust can absorb water, increasing the amount required to hydrate concrete to the point of workability, and so weakening the final hardened structure.
Consequently, WisDOT’s Standard Specifications regulate the level of microfines allowed in aggregates. Its PS200 test limits the amount of microfines passing a US #200 sieve to 1.5 percent of coarse aggregate weight, or 3 percent of fine aggregate weight when clays are present. Aggregates that do not pass this test must be washed before use to remove microfines.
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