Experiment 4: Evaluation of Effects of P200
on AASHTO T 84 Test Results
Experiment 4 was performed to (1) determine the amount
of P200 in a fine aggregate sample at which the P200 fraction
should be tested separately; and (2) conduct a sensitivity analysis
of the impact of P200 on the AASHTO T 84 test results.
Based on the sand equivalent test results shown in Table G-7
(Appendix G, available on the project web page), both the
Preston sandstone and RC limestone fine aggregates had
low sand equivalent values, which indicated the P200 fractions
contained significant amounts of clay-like material. The
blast furnace slag and Texas limestone sand had higher sand
equivalent values, which indicate that the P200 fines were not
clay-like. The natural sand had no clay-like material. The term
“clay-like material” is used in AASHTO T 176 for determining
the amount of plastic fines in soils and fine aggregate. This term
refers to the flocculated material in this test, and this flocculated
material may include other materials that are not clay.
The following materials were proposed in the testing plan
to assess the sensitivity and breakpoint of the P200 fraction:
• The fractions retained on the No. 200 sieve from the natural
sand and RC limestone fine aggregate. These materials
have the lowest and highest water absorption, respectively.
• The fine fraction passing the No. 200 sieve from the Texas
limestone. This is relatively clean with a minimum amount
of clay-like material.
• Clay used to determine the effect of clay present in P200
on the test results. Based on the panel’s recommendation,
sodium bentonite clay was used this study. The sodium
bentonite contains a significant amount of montmorillonite
that can absorb a large amount of water and swell
15 to 18 times its dry size. This sodium bentonite material
is commercially available and often used as a pond sealer.
The Atterberg limits (LL, PL, and PI) were conducted for
this material before it was used for testing in this study
(Table 3-34). The replacement rate was based on mass.
Figure 3-31 shows the laboratory testing plan for Experiment
4. The aggregate materials used in this testing plan are
shown in Table 3-35. The testing plan was conducted in the
following steps:
• Wash natural sand, RC limestone, and Texas limestone
sand over the No. 200 sieve.
• Keep the materials retained on the No. 200 sieve from the
natural sand and RC limestone and the P200 material from
the Texas limestone sand.
• Discard the P200 materials from the natural sand and RC
limestone and the material retained on the No. 200 sieve
from the Texas limestone sand.
• Create 12 blends for each of the two materials retained on
the No. 200 sieve (Table 3-35).
• Conduct AASHTO T 84 on the 24 blends (2 materials ×
12 blends/material) using three replicates.
• Conduct AASHTO T 84 on the two materials retained on
the No. 200 sieve (2 materials × 3 replicates = 6 tests).
• Conduct ASTM C110 on the clay and P200 material from
the Texas limestone sand (2 materials × 3 replicates = 6 tests).
• Determine the sand equivalent for the P200 material from
the Texas limestone sand (1 material × 3 replicates = 3 tests).
A detailed summary of the testing results for Experiment 4
is included in Appendix G, which is available on the project
web page. The following analyses were conducted to determine
(1) the impact of P200 on AASHTO T 84 test results and
(2) the amount of P200 at which the P200 fraction of the fine
aggregate should be tested separately.