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aggregate at an asphalt plant to produce a structural quality subbase or base course stabilized material.
The liquid asphalts (emulsified and cutback asphalts) may be plant mixed but are often in situ mixed for
less severe loading such as in the subgrade or the subbase or for lighter load applications. As a general
rule, the local paving grade asphalt cement will be appropriate for the binder for asphalt-cement
stabilization. For liquid asphalts, the highest possible viscosity liquid asphalt that can be handled in the
field and mixed with the soil or aggregate being stabilized should be used.
(3) Durability. Water may displace asphalt particles on a soil or aggregate particle in a process
known as stripping. Some aggregates have a strong affinity for water and tend to be particularly difficult
to coat with asphalt. They are prone to stripping and may prove impossible to coat with liquid asphalt.
Additions of lime or liquid antistrip agents or changing the charge of an emulsified asphalt may help
combat these problems. Potential moisture problems and effective countermeasures should be a
fundamental part of a bituminous stabilization laboratory evaluation and mix design.
(4) Suitable Soils. Bituminous stabilization is most effective with granular materials as excess
fines or plastic fines may make it impossible to properly mix the materials and require high binder
contents. As the plasticity index increases past 6 and the fines (percent passing the No. 200 sieve)
increases above 12 percent, problems with bituminous stabilization increase. In general, the plasticity
index should be below 10 and the fines should be less than 30 percent. As the plasticity and percent
fines increase, liquid asphalt become better stabilizing agents than asphalt cement. The plasticity of a
material to be stabilized can be reduced by adding lime.
n. Nontraditional Stabilizers. A wide variety of special, and often proprietary, stabilizers are
actively marketed. These materials have seen very little use or testing by the military, and no guidance
is currently available. Many, but not all, proprietary stabilizers that have been evaluated by the military
have not lived up to the manufacturer's claims, and no proprietary stabilizer should be used on a military
airfield without first evaluating it in the laboratory and in independent field trials. HQUSACE (CEMP-ET),
appropriate Air Force MAJCOM pavements engineer, or Naval Facilities Engineering Service Center
should be consulted prior to using any of these nontraditional stabilizers.
(1) Types: Nontraditional stabilizers include a wide variety of acids, salts, electrolytes (often a
sulfonated oil), polymers, enzymes, natural resins, cation exchange agents, lignins, and polymers
among others. Claimed benefits include strength gain, reduced water susceptibility, improved
compaction, reduced dusting, reduced plasticity, and better soil texture.
(2) Evaluation. The claimed benefit of any stabilizer should be evaluated quantitatively so that
the cost-effectiveness of including the material on a specific project can be determined. It is important to
identify what soil property is being changed by the stabilizer and develop a quantitative scheme for
evaluating this property. For example, electrolytes reduce a clay mineral's ability to hold water so they
have a potential role in dealing with expansive soils. A swelling test with and without the stabilizer is
appropriate to evaluate this stabilizer's effectiveness, whereas a strength test would provide no
information on the electrolyte's effectiveness. Experience with some of these materials has found that
often the amount of the stabilizer needed is higher than the manufacturer's suggested dosage.
3. PORTLAND-CEMENT CONCRETE. Portland-cement concrete is the surfacing for rigid pavement.
It carries load through bending and is the major structural component for supporting load. Unreinforced
concrete is generally the most serviceable and cost-effective surfacing for military airfields and will be
used in most circumstances.