30 June 2001
Minimum Unconfined Compressive Strength for Cement, Lime, Lime-Cement, and Lime-
Cement-Fly Ash Stabilized Soils
Minimum Unconfined Compressive Strength, psi1
Stabilized Soil Layer
Subbase course, select material
Unconfined compressive strength determined at 7 days for cement stabilization and 28 days for lime,
lime fly ash, or lime-cement-fly ash stabilization.
are usually made on soaked remolded samples; however, where existing similar construction is
available, CBR tests should be made in-place on material when it has attained its maximum expected
water content or on undisturbed soaked samples. The procedures for selecting test values described for
subgrades apply to select materials and subbases. Experience has shown that CBR tests on gravelly
materials in the laboratory have tended to give CBR values higher than those obtained in tests in the
field. The difference is attributed to the processing necessary to test the sample in the 152-millimeter
(6-inch) mold, and to the confining effect of the mold. Therefore, the CBR test is supplemented by
gradation and Atterberg limits requirements for subbases, as shown in Table 7-2. Suggested limits for
select materials are also indicated. In addition to these requirements, the laboratory CBR must be equal
to or higher than the CBR assigned to the material for design purposes.
Gradation and Atterberg Limit Requirements for Subbases and Select Materials
Maximum Permissible Value1
Size, mm (in.)
LL signifies liquid limit; PI signifies plasticity index.
EI 02C202/AFJMAN 32-1016 contains maximum values for open graded and rapid draining