Laboratory Characterization of Municipal Solid
Waste Incineration Ash
Sita Marie Syal, Mohammad Kabalan, Matt Hambright,
and Dr. Dimitrios Zekkos, P.E.
Department of Civil and Environmental Engineering, University of Michigan
Organic Content (ASTM D-2974)
Objectives
The objective of this study is to characterize the physical and mechanical
properties of municipal solid waste incineration (MSWI) ash. MSWI ash
consists of bottom and fly ash. The mixture of the two is known as combined
ash.
This test method is used to evaluate the amount of organics present in the
particulate material.
• Organic content is measured by heating a sample from 110oC to 440oC and
measuring the amount of material loss.
• Organic content values were generally between 1.5% and 2.6%
Proctor Compaction (ASTM D-1557, ASTM D-698)
Careful characterization of the ash may lead to a more efficient design of
monofills, and to possible reuse in major civil infrastructure such as levees,
highways, and embankments.
This test method is used to determine the compaction characteristics
(density and moisture) of particulate materials.
The study consists of:
a) A literature review of the characteristics of the MSWI ash
b) Testing of samples of ash from Carleton Farms Landfill in Michigan
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Surface Morphology using Scanning Electron
Microscopy
SEM uses an electron beam to form a detailed morphological image of the
material particles
Electron beams are focused and deflected when they come in contact with a
specimen. The deflected electrons are detected to produce images such as
those seen here.
These images of an MSWI ash sample were taken on the FEI Quanta 200 3D
at the Electron Microbeam Analysis Laboratory at the University of Michigan.
The following observations can be made:
• Bottom ash is porous, sub-angular to angular.
• These physical characteristics suggest relatively high frictional
characteristics
Modified Proctor
140
Dry Density (pcf)
Procedures and Results
Compaction Curves
Bottom Ash
Forrester & Goodwin (1990)
Izquierdo et al (2001), Matero
Izquierdo et al (2001), Sant Adria
Pandeline et al (1997)
Pandeline et al (1997)
Demars et al (1993)
Demars et al (1993)
Demars et al (1993)
Chesner and Eighmy (1989)
120
Combined Ash
Forrester & Goodwin (1990)
Chesner and Eighmy (1989)
This study (Sample #4)
Standard Proctor
Pandeline et al (1997) BA
Geosyntec (2004)
Pandeline et al (1997) BA
Izquierdo et al (2001) Sant Adria
Izquierdo et al (2001) Matero
This study (Sample #2)
This study (Sample #3)
40
This study (Sample #4)
100
80
0
10
20
30
Moisture Content (%)
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Bottom ash (red) tends to have higher dry density values than the finer
combined ash (blue).
The Modified Proctor Compaction curves for each type of ash (bottom and
combined) show variability in optimum dry densities that is comparable to
natural soils.
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Consolidated Drained Triaxial Test(ASTM D-4767)
This test method is used to determine the shear strength of earth
materials.
1500
σ3=50 kPa
σ3=100 kPa
σ3=200 kPa
Ash Sample 2: Retained in Sieve No. 20 Mag: 48x
Deviator Stress (KPa)
1250
Ash Sample 2: Retained in Sieve No. 20 Mag: 769x
No moisture
3
γd=13.4-13.7 kN/m
1000
750
500
250
0
Sieve Analysis (ASTM C-136)
Percent Passing (%)
This test method is used to evaluate the grain size distribution of particulate
materials.
Bottom Ash
Berg and Neal (1998)
Travar et al. (2009)
Zwahr (2004)
Forrester and Goodwin (1990)
Izquierdo et al. (2001)
Izquierdo et al. (2001)
Izquierdo et al. (2001)
Tay and Goh (1991)
Zhang et al. (1999)
Demars et al. (1993)
FL IT (report 1999)-Pinellas County
FL IT (report 1999)-Key West
FL IT (report 1999)-West Palm Beach
Pandeline et al. (1997)
Pandeline et al. (1997)
Gress et al. (1992)
100
80
60
40
20
0
300
PI Testing 2010-11
Sample 1
Sample 2
Sample 3
Sample 4
30
3
0.3
0.03
Particle Size (mm)
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Combined Ash
Travar et al. (2009)
Forrester and Goodwin (1990)
Forrester and Goodwin (1990)
PI's Testing
Fly Ash
Travar et al. (2009)
Chang and Wey (2006)
Chang and Wey (2006)
Chang and Wey (2006)
Goh and Tay (1993)
Goh and Tay (1993)
Tay and Goh (1991)
The Grain Size Distribution curves for each type of ash (bottom, fly and
combined) exhibit some, but not extreme, variability.
Fly ash is finer than bottom ash.
Data in the literature as well as experimental data from this study suggest
the MSWI ash classifies as a “well graded sand” with some gravel or silt.
As a consequence, it could be used as a fill material.
0
10
15
Axial Strain (%)
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The triaxial test data suggest a cohesion c=52.5 kPa (7.6 psi) and a
friction angle φ=45o.
These results indicate a high strength material, making it attractive for
reuse as a fill. Also, slopes of monofills may be stable at steeper slopes
than those used in Subtitle D landfills.
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Conclusions
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MSWI ash has:
• Low specific gravity
• Moderate variability in properties
• Coarse surface morphology
• Grain size distribution of a well graded sand
• No plasticity of fines
• High shear strength.
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Thus, MSWI ash properties seem to have attractive physical and
mechanical characteristics for reuse in civil infrastructure
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Monofill ash capacity may be higher than previously expected, as the ash
seems to be a strong material.
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Environmental considerations related to the reuse of the MSWI ash in
civil infrastructure need to be considered.
Acknowledgments
Specific Gravity
Specific gravity values of the MSWI ash in the literature suggest values
ranging between 1.5 and 2.5
Specific gravity values of the MSWI ash tested as part of this study suggest
values ranging between 2.1 and 2.6.
These relatively low values, suggest that the MSWI ash could be used as
lightweight fill.
5
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The authors are grateful to Mr. Matt Neely from Republic Services for
providing support to the field activities and sample collection at Carleton
Farms Landfill.