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stabilization results in granular layers sandwiched between relatively impervious layers (e.g., granular
base course between an asphalt concrete surface and a stabilized subbase), then this pervious
intermediate layer should be positively drained. Because of the potential for poor performance of such
geometries, such designs must be approved before use by HQUSACE (CEMP-ET), appropriate Air
Force MAJCOM pavements engineer, or Naval Facilities Engineering Service Center.
c. Terminology. The term "stabilization" as used in this chapter will encompass the addition of any
materials to a soil or aggregate to improve its strength or physical characteristics for use as pavement
subgrade, fill, subbase, or base course. As employed here, the term will include combinations with
common additives such as lime and portland cement or lime-portland cement-fly ash as well as those
materials often referred to as soil-cement, lean concrete base, econocrete, etc. TM 5-822-14/AFJMAN
32-1019 differentiates between soil stabilization and soil modification where the later only results in an
improvement in some property but does not by design cause a significant increase in strength. This
level of differentiation is not needed for the generalized discussion of the topic in this chapter, so
stabilization is used here as an all-inclusive term.
d. Seasonal Frost Areas. Use of stabilized materials in areas subject to seasonal frost must
address two extra concerns. First, the stabilized material must be durable for its intended purpose under
the freezing and thawing exposure to which it will be exposed. Secondly, many stabilizers (e.g., portland
cement or lime) must cure to gain strength, and the necessary chemical reactions to gain strength are
greatly retarded and may cease altogether at low temperatures. Consequently, some stabilized
materials placed late in the fall may not be able to gain adequate strength prior to the onset of freezing
weather. Consequently, local climatic conditions will determine a cutoff date well in advance of
anticipated freezing conditions after which date it is not prudent to place stabilized materials. Additional
assistance on problems with stabilized materials under seasonal frost exposure is available from the
Army Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755.
e. Combinations of Stabilizers. Under some circumstances, it may be desirable to use
combinations of stabilizers to take advantage of each stabilizer's characteristics (e.g., use of a
combination of lime and then portland cement relying on the lime to improve a plastic clay's workability
and the portland cement for more rapid strength gain than available from the slower pozzolanic reactions
of lime alone).
f. Mixing. The stabilizer and soil or aggregate to be stabilized may be mixed in situ or mixed at a
central plant and then transported to the construction site and placed according to the project
specifications. Proper mixing is crucial to stabilizers achieving their desired purpose. Central plants
provide the best and most consistent product. In situ mixing may vary from repeated working with a
grader to highly sophisticated mixers specifically designed for the task. It is harder to achieve good
distribution and mixing of the stabilizer with in situ mixing techniques than with plant mixing.
Consequently, stabilizer contents are sometimes increased to 1 percent over the laboratory
determined design stabilizer content to account for uncertainties of in situ mixing.
g. Compaction. Stabilized materials must be adequately compacted to achieve their desired
purpose. Stabilization is not a substitute for compaction, and poorly compacted stabilized layers are
prone to premature failure. Essentially, the compaction equipment and procedures and the quality-
control techniques used with conventional earthwork are adequate for stabilized materials. Compaction
equipment of sufficient size is needed, and lift thicknesses should be restricted to a maximum of
150 millimeters (6 inches) unless the contractor can demonstrate in the field that project specified
density levels are achieved throughout the lift for thicker placements. To check the latter, the density
must be measured in the bottom of the lift and not just at the surface or as an average through the entire