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from the resulting calcium silicate and calcium aluminate hydrate compounds. Soil compressive strength
gain, after 28-day cures at 22.8 oC (73 oF) from the pozzolanic reaction between lime and some clay
minerals may range from negligible to 10.34 MPa (1,500 psi). Typically, a well-compacted, reactive
lime-stabilized soil will achieve compressive strengths in the range of 100 to 500 psi.
(2) Uses. Lime added to soil can rapidly dry the soil; it coarsens the particle texture which
often makes the soil easier to work; and it reduces the soil's plasticity, making it more workable,
generally reducing the soil's strength loss when it is wetted, and often reducing adverse shrinking and
swelling behavior. The pozzolanic strength gain, which is typically assessed after 28 days of curing at
22.8 oC (73 oF), can significantly improve soil strength of subgrades and can often meet the strength
requirements for a stabilized subbase for flexible pavements. The requirements for stabilized bases are
harder to meet with lime alone, and the addition of cement with the lime may be needed to gain the
required strength. Many characteristics of lime stabilization make it very useful as a construction
expedient and soil improvement additive for difficult plastic clay soils (e.g., drying, coarser texture,
reduced plasticity and water susceptibility, construction platform, reduced shrink-swell behavior) rather
than for structural strength alone.
(3) Durability. Lime stabilization should provide sufficient durability to accomplish the required
objectives under the anticipated exposure conditions.
(a) Moisture. Lime-stabilized soils generally retain over two-thirds of their strength when
exposed to water and have performed well in structures exposed to water (e.g., levees, canals, and
dams and as expedient (lime-stabilized clay surface) military airfields in Latin America). However, a few
clays have shown poor strength retention when soaked in the laboratory. Consequently, some soaked
strength tests or the optional wet-dry test (ASTM D 560) limits in TM 5-822-14/AFJMAN 32-1019 may be
checked if strength when exposed to soaking or wetting and drying is a critical design parameter.
(b) Seasonal frost exposure. Lime-stabilized materials generally expand and lose
strength when exposed to freezing and thawing. As cycles of freezing and thawing increase there is a
progressive decrease in the strength of the lime-stabilized material. Generally, the first winter is the
critical exposure as extended curing in subsequent seasons will provide additional strength, and there
are data to suggest these materials may heal autogenously under favorable curing temperatures. TM 5-
822-14/AFJMAN 32-1019 has specific testing criteria and limits based on ASTM D 560 that must be met
if the lime-stabilized material is to be exposed to freezing and thawing. Because of the relatively slow
rate of pozzolanic strength gain in lime stabilization, adequate time for curing must be allowed prior to
the stabilized layer's being exposed to freezing. Consequently, the lime-stabilized material must be in
place well in advance (e.g., perhaps 30 days) prior to the onset of freezing weather which shortens the
construction season for some areas. Alternatively, it must be protected from freezing (e.g., by placement
of overlying pavement layers), and the temperature maintained high enough to allow pozzolanic
reactions to occur. Additional assistance on problems with lime-stabilized materials under seasonal frost
exposure is available from the Army Cold Regions Research and Engineering Laboratory, 72 Lyme
Road, Hanover, NH 03755.
(c) Leaching. There is some limited evidence that soils stabilized with low levels of lime
may have the benefits of lime stabilization reduced by leaching over time. The problem appears to be
relatively rare and generally associated with low levels of lime stabilization (e.g., 3 percent and less). In
general, this should not be an issue for lime stabilization levels for airfield pavements as their strength
and durability requirements would normally require lime contents above those where leaching has been
a reported problem.