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AASHTO T71 – Standard Method of Test for Effect of Organic Impurities in Fine Aggregate on Strength of Mortar


AASHTO T71 is a standard test method used to determine the effect of organic impurities in fine aggregates on the strength of mortar. This test is essential for assessing the suitability of fine aggregates, such as sand, for use in concrete and mortar. Organic impurities, originating from decomposed vegetable matter or other sources, can adversely affect the setting time, strength development, and overall performance of concrete and mortar.

Key aspects of AASHTO T71:

  • Purpose: the primary objective is to quantify the potential impact of organic impurities on the compressive strength of mortar. This is achieved by comparing the strength of mortar made with the fine aggregate as-is (unwashed) to the strength of mortar made with the same aggregate after washing to remove the impurities.
  • Test procedure: two sets of mortar specimens are prepared, one using the unwashed fine aggregate and the other using the washed aggregate. The specimens are cured under standard conditions and then tested for compressive strength at 7 and 28 days.
  • Strength ratio: the compressive strength of the mortar made with the unwashed aggregate is compared to that of the mortar made with the washed aggregate. A strength ratio is calculated, and the results are interpreted based on the specified acceptance criteria.
  • Significance: AASHTO T71 provides a reliable method for assessing the potential detrimental effects of organic impurities on the strength of mortar. If the strength ratio is lower than the specified limit, it indicates that the organic impurities are significantly impacting the mortar’s strength, and the aggregate may not be suitable for use in concrete or mortar unless further treatment is undertaken.

Applications of AASHTO T71:

  • Aggregate evaluation: this test is commonly used by aggregate producers and construction contractors to assess the quality of fine aggregates and ensure that they meet the required specifications for use in concrete and mortar.
  • Quality control: AASHTO T71 is an important quality control tool to identify and mitigate the potential negative effects of organic impurities on the strength and durability of concrete and mortar.
  • Research and development: the test method is also used in research and development to investigate the impact of different types and concentrations of organic impurities on the properties of concrete and mortar.

AASHTO T71 Accredited Laboratory

Applied Testing & Geosciences, LLC is accredited for performing tests using the AASHTO T71 standard.

Our laboratory offers comprehensive aggregate testing services, including the evaluation of organic impurities and their effect on mortar strength according to AASHTO T 71. Our experienced technicians utilize standardized procedures and calibrated equipment to provide accurate and reliable results, helping you ensure the quality of your aggregates and the long-term performance of your concrete and mortar.

Contact us for more information.



mortar strength; organic impurities; fine aggregate; compressive strength; washing; sodium hydroxide solution