Standard Method of Test for Determining the Plastic Limit and Plasticity Index of Soils
Standard Method of Test for Determining the Plastic
Limit and Plasticity
Index of Soils
AASHTO
AASHTO
Designation: T 90-16
Technical
Section: 1a, Soil and Unbound Recycled
Material
Release:
Group 3 (OCTOBER)
3.
APPARATUS
3.1.
Dish-A porcelain evaporating dish or similar mixing dish about 115 mm in
diameter.
3.2.
Spatula-A spatula or pill knife having a blade about 75 mm in length and
about 20 mm in width.
3.3. Surface for Rolling-Shall consist of
one of the following:
3.3.1. A ground glass plate or piece or piece of
smooth, unglazed paper on which to roll the sample. Paper, if used, shall not
add foreign matter (fibers, paper fragments, etc.) to the soil during the
rolling process and shall lay flat on a smooth horizontal surface.
3.3.2. Plastic Limit Rolling Device--- A device
made of acrylic conforming to the dimensions shown in Figure 1.
Dimensions:
IW ----- approximately 100 mm
L
----- Approximately 200 mm
T ---- 5 to10mm
H
----- 3.20 + 0.25 mm plus the total thickness of the unglazed paper
attached to the bottom plate. See Note 3.
W ----- See Note 1.
Notes:
The tolerance between the width of the top plate (W) and the inside width of the bottom plate (1W)
shall be such that the top plate slides freely on the rails without wobbling.
The top plate shall be rigid enough so that the thickness of the
soil threads is not influenced by flexure of the top plate.
The width of the side rails shall be between 3 and 6mm
Figure 1- Plastic Limit Rolling Device
3.3.2.1. Paper for Rolling Device-Unglazed paper
that does not add foreign matter (fibers, paper, fragments, etc.) to the soil
during the rolling process. Attach the unglazed paper to the top and bottom
plates of the device either by a spray-on adhesive backing.
Note 1-
Take special care to remove the adhesive that remains on the plastic
limit rolling device after testing. Repeated tests without such removal will
result in a buildup of the residual adhesive and a decreased soil thread
diameter.
3.4.
Moisture Content Container— made of material resistant to corrosion and
not subject to change in mass or disintegration on repeated heating and
cooling. The container shall have a close fitting lid to prevent loss of moisture
from samples before initial mass determination and to prevent absorption of
moisture from the atmosphere following drying and before final mass
determination. One container is needed for each moisture content determination.
3.5.
Balance— a class G1 balance meeting the accuracy requirements of
M231.
3.6
Oven—thermostatically controlled and capable of maintaining temperature
of 110 ± 5oC for drying samples.
4.
CALIBRATIONS, STANDARDIZATIONS, AND CHECKS
4.1.
Unless otherwise specified,
follow the requirements and intervals for equipment calibrations, standardizations,
and checks found in R 61.
4.2.
Follow the procedures for
performing equipment calibrations, standardizations, and checks found in R 61.
5. SAMPLE
5.1 If only the plastic limit is to be
determined—Take a quantity of soil with a mass of about 20g from the thoroughly
mixes portion of material passing the 0.425—mm (No. 40) sieve, obtained in
according with R58 or R74. Place the air---- dried soil in a mixing dish and
thoroughly mix with distilled, demineralized, or de—ionized water until the
mass becomes plastic enough to be easily shaped into a ball (Notes 2 and 3). Take a portion of this ball with a mass of about
10 g for the test sample.
Note
2---- Tape water may be used for routine testing if comparative tests
indicate on differences in results between using tap water and distilled,
demineralized, or de—ionized water. However, use distilled, demineralized, or
de—ionized water for referee or disputed tests.
Note
3---- The objective is to add enough moisture to a plastic soil sample so
that the 3—mm thread described in Section 6
does not crumble on the first roll. For a non-plastic soil, this will not be possible
5.2 If the plastic index (both liquid and
plastic limit) is to be determined—Take a test sample with a mass of about 10 g
from the thoroughly wet and mix portion of the soil prepared in according with
T89. Take the sample at any stage of the mixing process at which the mass
becomes plastic enough to be easily shaped into a ball without sticking to the
fingers excessively when squeezed. If the sample is taken before completion of
the liquid limit test, set it aside and allow to season in air until the liquid
limit test has been completed. If the sample taken during the liquid limit test
is too dry to permit rolling to a 3-mm thread as described in Section 6, add more water and remix (Note 3).
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