30 June 2001
strengths. If more rapid strength gain is needed, addition of 0.5 to 1.5 percent portland cement can be
used as an activator for the fly ash and as contributor to early-age strength.
(2) Uses. Pozzolans and slags gain strength more slowly than portland cement, but are more
economical, have less shrinkage and shrinkage cracking, and longer working times than portland
cement. Typical fly ash-stabilized mixes will use 2-1/2 to 4 percent lime with 10 to 30 percent fly ash.
Coarser soils and aggregates require less stabilizer than fine-grained soils. Some slag mixes used
overseas have 8 to 20 percent GGBF slag mixed with 1 percent lime.
(3) Durability. Because of the slower strength gain of these materials, it is crucial that sufficient
time be allowed between their placement and the onset of freezing weather. These chemical reactions
almost cease below 4.4 oC (40 oF) so this curing period must include moderate temperatures to assure
adequate curing of these materials. They can be vulnerable to freezing and thawing damage, so TM 5-
822-14/AFJMAN 32-1019 requires laboratory freeze-thaw testing after 28 days curing. Additional
assistance on problems with lime-pozzolan or slag-stabilized materials under seasonal frost exposure is
available from the Army Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover,
(4) Suitable Soils. Granular materials are effectively stabilized with these materials. Because
of their relative economy compared to portland cement, they are particularly effective with poorly graded
materials where they can effectively function as a filler more efficiently than the more expensive portland
cement. Many clays are naturally pozzolanic so there is little value in adding another pozzolanic
material like fly ash. These are usually best handled with lime alone. However, for clays that do not
develop pozzolanic reactions with lime or for silty materials that do not contain sufficient clay minerals to
react with lime, pozzolanic and slag stabilizers offer an economical and effective alternative to portland
m. Bituminous Stabilization. Asphalt cement (AASHTO PP6, ASTM D 3381, or ASTM D 946),
emulsified asphalt (asphalt emulsified with water, ASTM D 977 and D2397), or cutback asphalt (asphalt
dissolved in a solvent, D 2026, 2027, and 2028) may be mixed with a soil or aggregate to provide a
water resistant, cohesive stabilized material. The mix design for bituminous stabilized materials in a
military airfield subbase or base course will be done using a conventional Marshall mix design. Binder
contents for subgrade stabilization are often estimated on the basis of empirical equations and then
adjusted during construction in the field to achieve the desired results. TM 5-822-14/AFJMAN 32-1019
provides detailed guidance on bituminous stabilization requirements and procedures.
(1) Mechanisms. Asphalt coats the soil and aggregate particles being stabilized and binds it
into a water-resistant, cohesive material. Both strength and waterproofing are provided. No chemical
reactions are involved. Asphalt-cement stabilization requires no curing other than cooling. Liquid
asphalts require different amounts of curing depending on the emulsifying agent or solvent used and the
atmospheric conditions. The emulsion must break and the water must either evaporate or drain off for
the emulsified asphalt to be effective. Similarly, the solvent in cutback asphalts must evaporate.
Premature compaction of liquid-asphalt stabilized materials before adequate water or solvent
evaporation may cause very slow curing and leave the stabilized material too soft. The asphalt droplets
in an emulsified asphalt may have either a negative electric charge (anionic emulsion) or a positive
electric charge (cationic emulsion) that can be matched to the aggregate charge (e.g., an anionic
emulsion (negatively charged droplets) used with limestone aggregate (positive charge)).
(2) Uses. Asphalt stabilization provides cohesion to bind individual particles into a mass and
can provide significant waterproofing. Asphalt cements are generally mixed with a higher quality