The Superior Stabilizer

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The G.M. Boston Company International

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Stabilization Techniques:  Soil, Moisture Content and Compaction

Road Bed Stabilization

Road beds are often constructed with native site soils containing a wide gradation of materials which may include a high content of soil fines (passing 200 mesh).  Px-300 assists in binding fines together with larger materials into a dense, well-compacted material that provides a high degree of stabilization and higher tensile strength than untreated road beds.  PX300 road beds also offer a high resistance to moisture penetration (2.9 x 10-8 cm/sec under ASTM D 5084).  Benefits include reduced maintenance costs and utilization of on-site materials, eliminating the need to import off-site soil.  

Three important determine a stabilization result::

Material Gradation
Moisture Content
Compactive Effort

Material Gradation

Material Gradation refers to the distribution (% by weight) of the different sizes of particles within a given soil sample. A soil sample is well-graded if it contains a good, even distribution of particle sizes. A soil sample composed of predominantly one-sized particles is said to be poorly graded. A well-graded soil contains smaller particles which tend to fill the empty spaces between larger particles, leaving fewer voids after compaction.

The table below shows distribution guidelines for several different soil gradations.  

Sieve Size

Gradation (% passing)

� inch


1/2 inch 

 85 %  

No. 4 

 62 %  

No. 16  

 48 %  

No. 200

30 %  

Two conditions prevent  a successful stabilization:  The presence of large rocks; and certain types of contaminants. 

Large rocks can cause structural breakdown in an otherwise successful application and contaminants prevent the successful curing of the PX-300 solution in the treated soil. When either or both of these conditions are present, G.M. Boston Company requires prior notice of the fact, so that soil remediation can be done.

Moisture Content

PX300, enzymatic wetting agent and water are important components in any roadbed stabilization project.  These three components combine to lubricate the soil particles, helping them to slide into the voids between larger particles and produce the greatest density.  Soil fines and clay particles become "sticky" and cohesive, providing a necessary condition for stabilization.  Engineers have determined that almost all soils have what they call an optimum moisture content which permits maximum density from a given amount of compaction.  The illustration below shows the relationship between soil dry density and moisture content.

The presence of excess moisture in site soil due to flooding or heavy rainfall will prevent an efficient cure following the PX300 application.  If present site soil moisture plus the moisture accompanying a PX300 application will result in a moisture level well above optimum, the project should be deferred.  Usually two days of dry, moderately warm weather will bring the moisture level down to point that supports a successful PX-300 application.  

If flooding or heaving rainfall will closely follow a PX-300 application, that could also impair or prevent a successful PX-300 cure by diluting and washing away the uncured PX-300.  Accordingly, G.M. Boston Company strongly recommends a curing/drying period of 36-72 hours following a PX-300 application to ensure a successful project.

Without project conditions that comply with the guidelines stated above, G.M. Boston Company cannot provide assurance that a completed project will perform as expected by our customers and by us.  

Compactive Effort

Compactive effort is the process of physically increasing the weight per unit volume of road bed soil.  Compaction occurs in several ways:  a drum roller provides static weight or pressure,  a sheep foot roller provides a kneading action and a vibrating roller provides a shaking pressure.  All are acceptable compaction methods and occasionally, are used together for optimal results.  Without a proper moisture level, compaction cannot occur successfully.  If too wet, the compacted soil will push out from under the compaction equipment and, if too dry, the compacted soil will not hold together because it will lack the cohesive, "sticky" quality mentioned above in "Moisture Content."  The moisture density curve above has particular significance here.  

Building the Road

Road Bed materials using PX-300 should have a gradation mix that approaches the gradation specification values appearing in "Material Gradation."  Frequently, road beds have used materials outside design standards; these projects require prior sample testing to assess the likelihood of success.  Where outside soil will go on top of the existing road bed site soil, it is imperative to do sample testing of the imported soil to determine that PX-300 can achieve the customer's desired results before commencing the project itself.  

Generally, PX-300 is not recommended by compaction of lifts greater than 6 inches.  Type of material to be compacted plus the size and type of compaction equipment will determine lift thickness. 

Step 1:  Blade or rip the existing base to a depth of 6 inches, then windrow the loosened material.  If the project requires additional aggregate, the use the least-cost available material with more fines.  Check the overall gradation of the material to ensure that it conforms to the tested, pre-project sample.

Step 2:  For each acre of road base material, add 715 gallons of PX300 to the amount of water necessary to obtain optimum moisture.  Spray both the bladed surface and the windrow to reach optimum moisture.  Blend the PX-300 material using a grader blade, working the soil and aggregate back and forth to blend in the PX-300 and water.  If the material is too wet, blade until it approaches optimum moisture.  If too dry, add more PX-300 solution to bring the material up to optimum moisture.  After thorough mixing spread the material to grade.

Step 3:  Extend and crown the road bed surface with a blade.  If the material dries out on a hot day, spray again with the PX-300 moisture.  Compact with a sheep foot a pneumatic roller.  Use a vibratory roller for the first pass only and do not use vibratory compaction thereafter; additional vibratory compaction will cause cracking.  Compact in 6 inch lifts to ensure maximum compaction and, following the final pass, do not disturb the finished surface by attempting to "dress" minor imperfections.  If possible, allow the road bed to cure prior to use (and final testing).  Allowing the road base to dry (cure) will provide greater strength and decreased permeability.  

If intending to apply an asphalt or chip seal wear surface, moisten the road base surface with a diluted PX-300 application before applying the new wear surface.  That will ensure a better bonding of the two materials.


Contact us by phone or e-mail  for information about quantities and prices for your project.

G.M. Boston Company INTL, LLC
412 Fullerton
Newport Beach, CA 92663
Tel: (562) 592-0836
FAX: (949) 722-6799
Craig Hoad -
Greg Boston -