Environmental Acceptability of Precast Concrete Using

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Environmental Acceptability of Precast Concrete Using Powered By Docstoc
					  Environmental Acceptability of
     Precast Concrete Using
  Treated Municipal Solid Waste
     Incinerator Bottom Ash


                     August 1993



                 Chih-Shin Shieh, PhD
            Florida Institute of Technology


           State University System of Florida
              FLORIDA CENTER
FOR SOLID AND HAZARDOUS WASTE MANAGEMENT
             2207 NW 13 Street, Suite D
                Gainesville, FL 32609




                     Report #93-3
                                     ABSTRACT


        The study was conducted to provide information on the physical integrity and
leaching characteristics of precast ash-concrete products when they come in contact with
rainwater under natural conditions. Ash-concrete products used in the study included
hollow block, patio stone, and lawn edger. Municipal solid waste incinerator bottom ash
obtained from two operational facilities (one mass bum and one refuse derived fuel facility)
in Florida was stabilized with cement to fabricate precast ash-concrete products using
conventional concrete fabrication techniques.
        The test products were examined visually for any occurrence of cracking or
breakage. To monitor the leaching behavior of ash-concrete products in rainwater under
outdoor weathering conditions, duplicate product samples were put on the roof of the
Frueauff Building at Florida Institute of Technology. Similarly, products made of
conventional concrete were used for comparison. Each test product was placed in an
individual acid-cleaned plastic container. Beneath the individual test product, two sections
of PVC pipe were used to prevent the product from immersing in collected rainwater.
Collection of rainwater samples was conducted immediately after a rain fall (at least 0.5-cm
of water was accumulated). During sampling, volume of collected water sample and its pH
were recorded.
        Over the period of the study, no observed cracking of the ash-concrete product was
found. The ash-concrete product maintained its physical integrity after being exposed to
the natural environment for nearly one year. Studies conducted to monitor rainwater
leachate have shown that Ag, Cd , Hg. and Pb were not detectable in rainwater samples
collected throughout the study. Concentrations of As, Cr. Cu. Ni and Zn in rainwater
leachates were below the drinking water and U.S. EPA toxicity standards.



KEY WORDS: Municipal Solid Waste, Waste to Energy, Bottom Ash, Precast,
                       Ash-concrete, Stabilization, Recycling
                           EXECUTIVE SUMMARY


        The study was conducted to provide information on the physical integrity and
leaching characteristics of precast ash-concrete products when they come in contact with
rainwater under natural conditions. Ash-concrete products fabricated in the study included
hollow block, patio stone, lawn edger, sprinkler protector, and pelican statue. Products
used for rainwater monitoring were hollow block, patio stone, and lawn edger. Municipal
solid waste incinerator bottom ash obtained from two operational facilities (one mass bum
and one refuse derived fuel facility) in Florida was stabilized with cement to fabricate
precast ash-concrete products using conventional concrete fabrication technique.
        The ash samples were provided by the Pinellas County facility through Resource
Recycling Inc., St Petersburg, and the Palm Beach County facility and were shipped to
Florida Institute of Technology in the beginning of the project. After the ash was delivered
to the Ash Research Laboratory at Florida Tech, each sampIe was processed using
quartering and a mechanical spitter and stored in plastic containers. The samples were
sieved manually through l/2 in. and l/4 in. meshes to remove unburned materials and to
screen aggregates in different grain size from the ash matrix. Metals were sorted from the
ash by visual identification and the use of a magnet. Glass was identified by visual sorting.
It was noted that appearance of the ash grains and physical compositions of ash matrix
varied from facility to facility due mainly to the source of MSW burned and operational
conditions at each facility. After sieving, ash samples were mixed with cement and water
according to the formula developed in the previous study. Precast ash-concrete products
were made using conventional concrete fabrication techniques. The dimensions of hollow
block were 40 cm x 19 cm x 19 cm; the patio stone were 30 cm x 30 cm and lawn edger
were 63 cm x 13 cm.
        The test product were examined visually for any occurrence of cracking or
breakage. To monitor the leaching behavior of ash-concrete products in rainwater under
outdoor weathering conditions, duplicate product samples were put on the roof of the
Frueauff Building at Florida Institute of Technology. Similarly, products made of
conventional concrete were used for comparison. Each test product was placed in an
individual acid-cleaned plastic container. Beneath the individual test product, two sections
of PVC pipe were used to prevent the product from immersing in collected rainwater.
Collection of rainwater samples was conducted immediately after a rain fall (at least OS-cm
of water was accumulated). During each sampling, volume of collected water sample and
its pH were recorded. Collected water samples were then processed properly for later
determination of trace metals in the samples. An atomic absorption spectrophotometer
equipped with flame and furnace and operated with a computer was used for analysis.
        Over the period of the study. no observed cracking of the ash-concrete product was
found. The ash-concrete product has maintained its physical integrity after being exposed
to the natural environment for nearly one year. Studies conducted to monitor rainwater
leachate have shown that Ag, Cd, Hg and Pb were not detectable in rainwater samples
collected throughout the study. Concentrations of Cr, Cu, Ni. As and Zn in the rainwater
leachates were below the drinking water and U.S. EPA toxicity standards.
        The overall results have indicated that municipal waste incinerator bottom ash can
be used as an aggregate and can be mixed with Portland cement and water to fabricate
precast ash-concrete using conventional concrete techniques. This makes the approach of
using bottom ash to fabricate precast ash-concrete product more economically feasible. As


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long as the physical integrity of the product is maintained, there will be no concern of
adverse effect on the environment because of the leaching of trace metals from the product
when it comes in contact with rainwater.




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