AASHTO T90

Full Name

AASHTO T90 – Standard Method of Test for Determining the Plastic Limit and Plasticity Index of Soils

Scope

AASHTO T90 is a standard test method used to determine the plastic limit (PL) and plasticity index (PI) of soils. These parameters are part of the Atterberg limits, which provide crucial insights into the behavior and characteristics of fine-grained soils. Understanding the plasticity of soils is essential for various geotechnical engineering applications, including the design of embankments, foundations, and pavements.

Key aspects of AASHTO T90:

  • Plastic Limit (PL): the plastic limit is the lowest moisture content at which a soil can be rolled into a thread of approximately 3.2 mm (1/8 inch) in diameter without crumbling.
  • Plasticity Index (PI): the plasticity index is the numerical difference between the liquid limit (LL) and plastic limit (PL) of a soil. It indicates the range of moisture content over which the soil exhibits plastic behavior.
  • Test procedure: the test involves rolling out a soil sample into a thread of decreasing diameter until it crumbles. The moisture content at which the thread crumbles is determined and repeated for multiple trials to obtain an average value. This average value represents the plastic limit. The plasticity index is then calculated by subtracting the plastic limit from the liquid limit obtained from AASHTO T89.
  • Significance: the plastic limit and plasticity index provide valuable information about the soil’s workability, shrink-swell potential, and overall behavior under different moisture conditions. This data is essential for selecting appropriate soils for specific applications and optimizing their engineering properties.

Applications of AASHTO T90:

  • Soil classification: the plastic limit and plasticity index are key parameters in classifying fine-grained soils according to their plasticity characteristics. This classification helps engineers select suitable soil types for various projects and predict their behavior under different conditions.
  • Geotechnical design: the Atterberg limits are used in geotechnical design calculations for embankments, foundations, and pavements. This data helps engineers assess the potential for settlement, stability issues, and other risks associated with soil behavior.
  • Quality control: the test is also used to ensure that the soil materials used in construction projects meet the specified plastic limit and plasticity index requirements.

AASHTO T90 Accredited Laboratory

Applied Testing & Geosciences, LLC is accredited for performing tests using the AASHTO T90 standard.

Our laboratory offers comprehensive soil testing services, including the determination of plastic limit and plasticity index according to AASHTO T90. Our experienced technicians utilize standardized procedures and calibrated equipment to provide accurate and reliable results for your geotechnical projects.

Contact us for more information.

Resources

Keywords

plastic limit; plasticity index; soil; Atterberg limits; liquid limit; rolling thread; moisture content; crumble

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