United States Department of Transportation
i
Development of a Test to Quantify Organic Content in Silica Sand
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2022-09-08
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[PDF-961.10 KB]
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Edition:Draft Final Report; Technical Memorandum
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Abstract:Fine aggregates used for concrete can sometimes contain organic matter that can inhibit the cement hydration reactions and reduce strength. AASHTO T 21 and AASHTO T 71 have been developed as screening tests for fine aggregate organic matter and quality. The objective of this research project is to determine whether a modified Walkley Black test or Elemental Analysis of carbon test can be used as a substitute test for the AASHTO T 21 or AASHTO T 71 tests. Organic content for 18 fine aggregate samples from Florida and Georgia were measured using the Modified Walkley Black method and Elemental analysis via combustion and compared to the results of AASHTO T 21 and AASHTO T 71. A good correlation was found between the Modified Walkley Black method and Elemental analysis via combustion and AASHTO T 21, however none of the tests correlated well with AASHTO T 71. Isothermal calorimetry performed on mortar samples did not show that the fine aggregates caused any cement hydration retardation or interference with the cement hydration reaction. Any mortar strength loss must be due to other factors that should be investigated in the future.
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