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Applications  > Soil Stabilization/Solidification
Cement aids site rehabilitation
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soil stabilization green design
An In-Situ blender head is used to mix cement into soil at a former wood treating facility in New Jersey.
Solidification/Stabilization (S/S) is a treatment technology for contaminated soils, either for clean up/remediation alone or as part of a brownfield redevelopment. Portland cement, often augmented with other materials, such as fly ash, lime kiln dust, cement kiln dust, and lime, is used as a binding reagent in S/S because of its ability to both solidify -- change the physical properties -- and stabilize -- change the chemical properties-- of a wide range of hazardous materials.  Solidification increases the compressive strength, decreases the permeability, and encapsulates toxic elements.  Stabilization converts hazardous elements into less soluble, mobile or toxic forms.  Mixing the right combination of binding reagents into contaminated soils allows them to be either excavated and disposed of in a landfill, or re-used on site to support redevelopment.  The solidification treatment has the further benefit of improving the structural properties of the site as well.
uses

 

S/S is used to remediate or reclaim a contaminated site. Specific treatment effects include:
 
 
  • Chemically binding free liquids in waste material
  • Reducing the permeability of waste matter
  • Encapsulating waste particles
  • Chemically fixing hazardous elements
  • Helping reduce the toxicity of contaminants.
why

S/S is identified as  a Best Demonstrated Available Technology for 57 of the 500 specific waste materials listed under RCRA (Resource Conservation and Recovery Act).  In addition to “listed” wastes, RCRA identifies “characteristic” wastes,  which are less common, so not listed, but have some characteristic (e.g. ignitable, explosive/reactive, corrosive),  that is cause for concern and special handling. S/S can often be used to eliminate this characteristic, thus reducing disposal costs or enabling re-use.  One of its great strengths as a treatment technology is the ability to handle so many different chemicals. The physical and chemical properties of cement make it particularly suited to solidification and stabilization of hazardous materials because it is multifaceted in the way it reacts with  other materials, either binding them – locking up free liquids and organic contaminants; or  encapsulating them  or chemically transforming them  - in the case of heavy metals and other inorganics.
The improved compressive strength of this type of soil treatment versus other treatment methods, can serve to improve the site conditions for development in addition to treating the contamination.

sustainability

 

S/S treatment has been used at the New York Harbor system to turn dredged harbor sediments nto an engineered fill.  The engineered fill was used to rehabilitate a "brownfield" property.  PCA Noo. 11002
While both clean up and reclamation contribute to environmental stewardship, reclaiming contaminated land for redevelopment is particularly key to a sustainable development strategy.  Concerns about liability and cost for dealing with contaminated, or even potentially contaminated land is a deterrent to in-fill projects and helps drive developers to ‘greenfield’ or previously undeveloped land.  This contributes to sprawl, where development density is too low and spread out to support the water, sewer and transportation infrastructure needed to service it.  Sprawl permanently converts agricultural or forest land on an ever expanding urban fringe to development.  By facilitating the reclamation of  previously used sites, S/S helps clean up and rejuvenate ‘wasted’ urban land.  Using 'brownfield' sites may contribute to LEED Credit SS 2.

considerations

Right mix for the job. Portland cement is often combined with other inorganic reagents to achieve the intended mix of treatment objectives for the particular suite of hazardous materials in question.

Testing: Final performance testing of  the treated waste is required.  Standard tests can include the paint filter test, hydraulic conductivity, and unconfined compressive strength to determine physical performance.  Toxicity Characteristic Leaching Procedure (TCLP) or Synthetic Precipitation Leaching Procedure (SPLP) are used to  evaluated the chemical performance of the treatment.  The former simulates leaching conditions of landfill disposal, while the latter is intended to simulate acid rain and is more appropriate for reclaimed soil that will be left  in-situ (on-site) and reused.

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Resources
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Download DocumentPhoenix-Award Winning Kendall Square Rises from the Cement-Treated Brownfield Site (2006)
By Christopher Carleo and Thomas Clark of The RETEC Group, Inc., and Charles M. Wilk Portland Cement Association. (2006) Item Code SR854, 2 pages
Free to download. The Kendall Square Redevelopment project in Cambridge, MA was named the Grand Prize winner of the ten regional Phoenix Award winners at the EPA-sponsored Brownfields 2006 Conference. As a former location of a manufactured gas plant, property soil was impacted with coal tar to a depth of over 20 feet. The property was remediated using cement-based insitu solidification/stabilization treatment. The Phoenix AwardsTM is considered the pinnacle of achievement of excellence in brownfield redevelopment and often is called the brownfields’ equivalent of Hollywood’s Oscars. The remediated property is now the site of a Leadership in Energy and Environmental Design (LEEDTM) Platinum-certified office building.