Evaluation of Lime Kiln Dust as a Mineral Filler in Stone Matrix Asphalt

EVALUATION OF A LIME KILN DUST AS A MINERAL FILLER
FOR STONE MATRIX ASPHALT
Randy C. West and Robert S. James
Randy C. West
National Center for Asphalt Technology
277 Technology Parkway
Auburn, AL 36830
Telephone: 334-844-6228
Fax: 334-844-6248
E-mail: westran@auburn.edu
Robert S. James
APAC, Inc.
3006 Port Cobb Drive
Smyrna, GA 30080
Telephone: 404-603-2771
Fax: 404-603-2770
E-mail: rsjames@ashland.com
July 2005
Submitted for presentation and publication at the 85 th Annual Meeting of the
Transportation Research Board, Washington, D.C., January 2006
(3,545 words + 8 tables + 4 figures =6,545 words)
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West and James 1
EVALUATION OF A LIME KILN DUST AS A MINERAL FILLER FOR STONE
MATRIX ASPHALT
Randy C. West and Robert S. James
ABSTRACT
Lime kiln dust (LKD) has had limited use as a mineral filler in Stone Matrix Asphalt (SMA).
Although LKD meets mineral filler requirements of most agency specifications, a few cases of
premature pavement failure have been attributed to some lime kiln dusts having high percentages
of available lime. This study compared a lime kiln dust to a common rock dust mineral filler
using basic asphalt mix design tests. Since the problem with SMA containing LKD with high
available lime content occurs when the pavement is wet, specimens were conditioned with
numerous freeze-thaw cycles and extended soak times to evaluate potential reactions under harsh
conditions. The results show that the LKD used in this study performed as well or better than the
rock dust mineral filler. The standard tensile strength ratio test is capable of identifying LKD
with high available lime contents that will not perform well. Further research is needed to
determine a suitable maximum limit for available lime content of LKD for use as a mineral filler
for SMA.
KEYWORDS: Lime Kiln Dust, Mineral Filler, SMA, Available Lime, Tensile Strength Ratio
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EVALUATION OF A LIME KILN DUST AS A MINERAL FILLER FOR STONE
MATRIX ASPHALT
Randy C. West and Robert S. James
INTRODUCTION
Stone Matrix Asphalt (SMA) is a premium type of hot mix asphalt pavement. One of the
component ingredients in SMA mixtures is mineral filler. Mineral fillers combine with the
asphalt, fibers, and a small percentage of fine aggregate particles to create a binder rich mastic
which fills the void spaces between the coarse aggregate skeleton. The requirements for mineral
filler are not complex (1, 2). Consequently, a variety of materials have been used as mineral
fillers in SMA including rock dust products of various mineralogies, fly ash, Portland cement,
kiln dusts, and agricultural lime. Lime kiln dust (LKD), a by-product of lime manufacturing, has
been used as a mineral filler in SMA in a few cases. However, information from published
research studies or from field experience on the use of lime kiln dust in SMA is quite limited at
this time.
The objective of this research was to evaluate a lime kiln dust as a mineral filler in an SMA
using basic tests for asphalt mix design and evaluation. The laboratory evaluation consisted
comparing an SMA mixture containing LKD with the same mixture containing a commonly used
rock dust mineral filler. The SMA mixtures were subjected to additional testing to assess how
the mixtures may perform under severe conditions. Tasks established for the research included
the following:
1. Prior studies and experience with the use of lime kiln dust mineral filler containing
calcium oxide (CaO) in SMA mixtures were investigated.
2. Basic physical characteristics of a LKD and a common SMA mineral filler were
compared.
3. SMA mix designs were performed with a LKD and with the common mineral filler.
4. Moisture damage susceptibility of the test mixtures were determined using the standard
protocol in AASHTO T 283. Further conditioning sequences of extended hot water soak
times and additional freeze-thaw cycles were used to evaluate potential reactions of the
mineral fillers in harsh conditions.
5. Swell tests were performed on the test mixtures to evaluate possible volume change of
the specimens due to the reaction of free lime in the LKD.
6. Hamburg Wheel Tracker tests were conducted to further evaluate moisture damage
potential of the test mixtures.
Lime Kiln Dust Production
Lime kiln dust is a fine co-product of lime production. LKD is most commonly generated in
high temperature rotary kilns and captured in air pollution control systems such as cyclones,
baghouses, and electrostatic precipitators (3). LKD can be generally categorized based on its
reactivity which depends on the available (free) lime or magnesia content. The chemical
composition of a LKD is a function of characteristics the raw material feed (most often limestone
rock) and operating parameters of the kiln (4). Each year, an estimated 2.5 million metric tons of
LKD is produced in the United States (4). LKD is used for a variety of beneficial purposes,
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West and James 3
including soil conditioning and stabilization, industrial waste stabilization, Portland cement
production, and agricultural uses. Unused LKD is usually stockpiled near the lime plant but can
be disposed of in approved landfills.
Case Studies of the Use of Lime Kiln Dust as a Mineral Filler in SMA
Alabama
Lime kiln dust was used in several SMA projects in Alabama between 2001 and 2002.
According to the Alabama Department of Transportation, a number of these SMA projects
exhibited discolored surfaces soon after construction. The discoloration was generally observed
as a blotchy grey color. One Alabama project with lime kiln dust did result in more significant
pavement problems. This SMA project was constructed on Highway 80 in Selma, Alabama in
the summer of 2002. This project was intended to correct significant rutting on this heavy
trafficked section of roadway. The existing rutted pavement was milled five inches and two
layers of SMA were placed to complete the reconstruction. The first layer was a 1-½ inch
Maximum Aggregate Size (MAS) SMA which was placed 3 to 3.5 inches thick. The surface
layer was a ½ inch MAS SMA that was placed 1.5 to 2 inches. The 1-½ inch SMA mix
contained nine percent lime kiln dust and the ½ inch SMA mix contained six percent lime kiln
dust. In less than one year after construction, several areas of distress were observed. Flushing
of the surface was observed, followed by rutting, shoving, cracking, and potholes. A light tan
powder was evident along the edge of pavement in the distressed areas. Cores taken from the
pavement in the distressed areas found that the underlying SMA layer was severely stripped. It
was suspected that the lime kiln dust in the first layer of SMA contained excessive amount of
available calcium oxide. The Alabama Department of Transportation subsequently disapproved
LKD as a mineral filler for SMA mixtures.
Texas
In August 2003, an SMA project was started on SH-105 in Sour Lake, Texas. Paving of the
SMA began with a test section on the project located. The construction of the SMA test section
was cut short due to extended heavy rains in the area. A few days after the rain, the entire
surface of the SMA pavement had turned a grayish white color. The surface of the SMA was
friable and the test section had to be removed and replaced. The investigation of the failure led
to the mineral filler which was determined to be a lime kiln dust. Subsequent tests on samples of
the LKD from the contractor’s mineral filler silo indicated the LKD contained 54 percent
available calcium oxide content, an unusually high amount. The SMA mix design and TSR tests,
which had been conducted several months before, did not indicate any problems. However, lab
tests with the QC samples of the SMA did reveal that the mix was reactive in water. It was
apparent that the characteristics of the LKD mineral filler had changed from the time the mix
designs were performed and when the mineral filler was delivered to the contractor’s plant.
Kentucky
In September 2004, a project using lime kiln dust in SMA was completed on AA highway near
Bracken, Kentucky. The mix design contained six percent lime kiln dust and the available lime
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content for this mineral filler was between 20 and 22 percent. No problems were encountered
with the use of lime kiln dust at any point in the project. Mix production went well and target
roadway densities were met despite a 45 mile haul. Production volumetric properties were very
consistent and on target. The pavement has performed very well to date. No pavement
discoloration has been observed.
LABORATORY EVALUATION
Physical Characteristics of LKD and Marble Dust
Key physical characteristics of the mineral fillers including gradation, specific gravity, and
Rigden voids were determined. The gradations of the mineral fillers were determined using a
Coulter Model LS-200 particle size analyzer. Specific gravities of the mineral fillers were
determined using the method described in section 21 of ASTM C 110-00. The Rigden voids test
was performed on both mineral fillers in accordance with the procedure described in NAPA
publication IS 101 (8).
SMA Mix Designs
The SMA component materials selected for this study included a standard set of materials used
by NCAT in several other SMA research studies. Information on the materials is provided in
Table 1. The asphalt binder used in the study was a PG 67-22. Most agencies would normally
specify a higher PG grade, such as a PG 76-22 instead of the PG 67-22 for highway construction
projects. However, the PG 67-22 was intentionally selected because it was believed that the
softer asphalt grade would accentuate the effects the mineral fillers in the subsequent moisture
susceptibility tests. Mix designs were completed in accordance with AASHTO PP 41 Designing
Stone Matrix Asphalt (6). Samples were compacted in a Superpave Gyratory Compactor to 75
gyrations.
Moisture Damage Susceptibility
A series of tests were performed to assess the potential for moisture damage and/or reactions of
available lime with water for the SMA mixtures. The first series of tests utilized the industry’s
most commonly specified moisture damage test, AASHTO T283. This test is also referred to as
the modified Lottman test or the TSR (tensile strength ratio) test. Additional moisture damage
susceptibility tests were performed with harsher conditioning procedures. Conditioning and
testing of these specimens followed the procedure in AASHTO T 283 except that one set of
specimens was subjected to two freeze-thaw cycles and another set was subjected five freezethaw
cycles before the conditioned tensile strengths were determined. Another series of TSR
specimens were subjected to one freeze-thaw cycle, but the hot water soak period was extended
for 48 and 96 hours.
Samples of the SMA mixtures with the LKD and rock dust were also prepared and tested
to evaluate the potential for expansion due to reaction of free lime in the mineral filler with
water. Samples were compacted in the Superpave Gyratory Compactor in the same manner as
for T283. This yielded 150 mm diameter specimens with approximately 6% air voids and 95
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mm in height. Three specimens were prepared and tested for both mixtures. The specimens
were then placed in California Bearing Ratio (CBR) molds and the molds were submerged in
25ºC water. No surcharge weights were placed on the top of the SMA samples allowing free
expansion of the samples in the vertical direction. Periodic measurements were made of the
specimen heights using the CBR swell apparatus.
Samples of both test mixtures were also prepared and tested in the Hamburg Wheel
Tracking Device (HWTD) in accordance with AASHTO T 324-04. Two slabs for each test
mixture were compacted to 7±1.0% air voids with a rolling-wheel, kneading slab compactor.
Hamburg tests were performed at 50ºC. Results of the initial duplicate samples were
significantly different, so additional samples were tested. The air void content of the additional
samples were outside of the target range of 7±1.0% desired for this study, but were within the
wider range of 7±2% allowed by the test method.
RESULTS
Physical Characteristics of the LKD and the Rock Dust
Test results on the LKD and rock dust mineral fillers are provided in Table 1. The test results
show that the particle size distributions for the two mineral fillers are similar. The apparent
specific gravity of the LKD sample is slightly lower than the rock dust which indicates that for
an equivalent mass of mineral filler, the LKD will occupy a slightly higher volumetric proportion
in an SMA mixture.
The Rigden voids test evaluates the packing behavior of mineral fillers and provides an
indication of the shape of the mineral filler particles. According to research conducted in
NCHRP 9-8, Rigden voids is a good indicator of how much the filler will stiffen the asphalt
binder (9). The recommendation from this work was that fillers with Rigden voids above 50
may cause the mortar to be excessively stiff and difficult to work. Although the Rigden voids
result for the LKD mineral filler was higher than the result for the rock dust, the LKD is below
the recommended limit.
A chemical analysis of the LKD was done by the supplier in accordance with ASTM C
25 and C 1301. The tests indicated an available lime content (CaO) of 19.9 percent.
SMA Mix Designs
The optimum asphalt content for SMA mixtures, according to AASHTO PP 41, is based on an
air void content of 4.0%. To achieve 4.0% air voids, the optimum asphalt content for the LKD
SMA mix was 6.4%, and the optimum asphalt content for the rock dust SMA mix was 6.6%.
The slight difference in optimum asphalt content for the two mixtures is attributed to the
differences in specific gravity for the two mineral fillers. Since the LKD had a slightly lower
specific gravity, it occupied a slightly greater volume in the compacted mix, leaving slightly less
space for asphalt binder. Both mixtures met the mix design requirements for SMA (7). Based
on the mix design results, the LKD seems to behave very similar to the rock dust mineral filler.
The expected stiffening effect of the higher Rigden void result for the LKD was not apparent in
the mix design properties.
Moisture Susceptibility Testing
Tensile Strengths and Tensile Strength Ratios
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The results of the standard AASHTO T 283 test, shown in Table 5, indicate that there were no
problems with moisture susceptibility of the test mixtures. The results of the LKD SMA were
practically the same as for the marble dust SMA. As an additional point of comparison, TSR
tests were also conducted using a sample of the LKD from the Texas project with a very high
available lime content. To differentiate this high available lime LKD from the LKD used
throughout this study, it is referred to here as XLKD. Other than the source of the LKD, these
samples were prepared and tested exactly like the samples with the other mineral fillers. TSR
results for the XLKD are shown in Table 6. As can be seen, the average unconditioned strength
for the XLKD samples is very similar to those of the samples using the other two mineral fillers.
However, the average conditioned strength was very low, yielding a TSR of 0.25. This result
clearly demonstrates the problem with lime kiln dust containing high percentages of available
lime.
Additional moisture damage susceptibility tests were performed with harsher
conditioning procedures. For the first series of harsh conditioning, specimens were prepared
following AASHTO T283, then subjected to multiple freeze-thaw cycles before the conditioned
tensile strengths were determined. The conditioned strengths for the specimens subjected to
additional freeze-thaw cycles are illustrated in Figure 1. As expected, these results indicate that
the additional freeze-thaw cycles cause a reduction in tensile strengths. However, the loss of
strength was much less for the LKD SMA mixture.
For the second series of harsh conditioning, TSR specimens were subjected to one freezethaw
cycle, then conditioned in hot water for extended times. These results, shown in Table 7,
indicate that extending the soak time to 48 hours causes some loss of strength, but that as the
soak time is extended further to 96 hours, the tensile strengths increase. For the LKD SMA, the
tensile strength after the single freeze-thaw cycle and 96 hour soak was back to the
unconditioned tensile strength. The rock dust SMA also had some regain of strength after the 96
hour soak, but it had not recovered as well as the LKD SMA.
Interestingly, the LKD SMA samples subjected to the extended soak periods also showed
some discoloration on the surface of the specimens. As shown in Figure 2, the LKD SMA
specimens had a blotchy white coating apparently from leaching of some lime from the mineral
filler. This is believed to be similar to the appearance of discoloration of some lime kiln dust
SMA projects in the field. However, as evident from the tensile strength results shown above,
this discoloration does not appear to be detrimental to the integrity of the mixture.
Swell Tests
Results of the swell tests, illustrated in Figure 3, show that most of the volume change occurs in
the first day. The figure also shows that the expansion of the LKD MA mixture was less than
half of that for the rock dust SMA. This indicates that the small amount of available free lime in
the LKD mineral filler is not detrimental to the mixture.
Hamburg Wheel Tracking Tests
Typical Hamburg WTD results are shown in Figure 4. Hamburg WTD results are commonly
analyzed by determining two parameters: the rutting rate and the stripping inflection point (SIP).
For this study, the rutting rate is not important since we were primarily interested in evaluating
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West and James 7
the stripping susceptibility of the mixtures. Evaluating the rutting rate of these mixtures was not
appropriate since the softer PG 67-22 binder grade was intentionally selected to better
discriminate issues with moisture damage. The Hamburg WTD stripping inflection point results
and air voids for each sample are shown in Table 8. On average, the SIP results for the mixtures
with the two mineral fillers were similar. The results of the Hamburg tests, however, are highly
variable. The Hamburg results for these two mixtures would have been much better if a polymer
modified asphalt, as typically used in SMA mixtures, had been used instead of the unmodified
PG 67-22 binder.
Discussion
An investigation of field experiences with lime kiln dust found only a limited number of projects.
A few problems have been reported with the use of some lime kiln dusts used as a mineral filler
in SMA mixtures. Some field projects with lime kiln dust in SMA have resulted in premature
pavement failures; others projects have only left the pavement discolored, but with no evidence
of distress. Still other field projects have had not problems at all.
Comparisons were made between a lime kiln dust and a rock dust for use as a mineral filler
for SMA mixtures. SMA mixtures with these two materials were subjected to a variety of tests
and harsh conditioning sequences to evaluate the potential for adverse reactions and loss of
mixture integrity.
1. The physical properties of the lime kiln dust were similar to those of the rock dust
mineral filler. The Rigden voids test results indicate that the LKD particles may be more
angular than the rock dust. Although this may be expected to stiffen the binder, this
effect was not apparent in any of the mix design results.
2. The LKD mineral filler evaluated in this study behaved very similar to a commonly used
rock dust mineral filler when included in an SMA mixture. The mineral fillers resulted
similar optimum asphalt contents, volumetric properties, and tensile strength ratios.
3. When moisture damage susceptibility specimens were conditioned by extending the
soaking period at 60ºC from 24 hours to 48 hours, the tensile strengths of the LKD SMA
and the Rock Dust SMA dropped 13% and 23%, respectively. However, more samples
were soaked at 60ºC for 96 hours, and the tensile strength of LKD SMA improved to
slightly better than the tensile strength for the 24 hour soak. The tensile strength for the
96 hour soaked Rock Dust SMA also improved relative to the 48 hour soak, but remained
12% lower than the 24 hour soak tensile strength.
4. Discoloration of some LKD specimens was evident after soaking. Surfaces of the
specimens were blotchy white to grey. However, this discoloration did not correspond to
a loss of strength for the mixture.
5. When moisture damage susceptibility specimens were conditioned by additional freezethaw
cycles, the loss of tensile strength for the LKD SMA was much less than for the
Rock Dust SMA. This indicates that the LKD provides some benefit in resistance to
moisture damage.
6. The swell of SMA mixtures was also monitored over a period of four to five days. These
results showed that swell of the LKD SMA mixture was less than half of the swell for the
Rock Dust SMA.
7. Although the results of Hamburg wheel tracking tests were highly variable, the SMA
mixtures with LKD and Rock Dust appear to provide similar Stripping Inflection Points.
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West and James 8
The performance of these mixtures in this test would likely have improved dramatically if
a polymer modified asphalt binder had been used in the mixtures.
CONCLUSIONS AND RECOMMENDATIONS
Laboratory tests indicate that some lime kiln dust can be a suitable mineral filler for stone matrix
asphalt. In some cases, LKM may improve the SMA resistance to moisture damage. However,
not all lime kiln dusts are the same and may perform differently in laboratory tests and field
conditions. Some premature failures of SMA pavements have been attributed to some LKD’s,
while others have performed satisfactorily. Basic TSR tests can identify problem LKD
materials. The available calcium oxide content is believed to be a critical factor for whether or
not the LKD is suitable for use as a mineral filler. Further research is needed to better establish
an appropriate limit for the available lime content.
ACKNOWLEDGEMENTS
Funding for this study was provided by Carmeuse Lime Company. The authors gratefully
acknowledge their support for this project.
REFERENCES
1. MP 8-04 “Designing Stone Matrix Asphalt”, AASHTO Provisional Standards, June 2004
Edition, American Association of State Highway and Transportation Officials, June 2004.
2. Designing and Constructing SMA Mixtures – State of the Practice, Quality Improvement
Series 122, National Asphalt Pavement Association, March, 2002.
3. “Kiln Dusts - Asphalt Concrete User Guideline” internet document,
www.tfhrc.gov/hnr20/recycle/waste/kd2.htm
4. Miller, M. M., and R. M. Callaghan, “Lime Kiln Dust as a Potential Raw Material in
Portland Cement Manufacturing” Open File Report 2004-1336, U.S. Department of the
Interior, U.S. Geological Survey, 2004.
5. Collins, R., and S. Cielielski, “Recycling and Use of Waste Materials and By-Products in
Highway Construction”, NHHRP Synthesis 199, Transportation Rsearch Board, 1994.
6. Brown, E.R., Haddock, J.E., Crawford, C, Hughes, C.S., Lynn, T.A., and Cooley, L.A.,
“Designing Stone Matrix Asphalt Mixtures, Volume 1- Literature Review, Final Report”,
NCHRP 9-8/1, Transportation Research Board, July 1998.
7. PP 41-01 (2003), “Designing Stone Matrix Asphalt (SMA)”, AASHTO Provisional
Standards, June 2004 Edition, American Association of State Highway and Transportation
Officials, June 2004.
8. Brown, E.R. and Cooley, L.A., “Designing Stone Matrix Asphalt Mixtures for Rut Resistant
Pavements”, NHCRP Report 425, Transportation Research Board, 1999
9. Anderson, D., “Guidelines on the Use of Baghouse Fines”, Information Series 101, National
Asphalt Pavement Association, February, 1991.
10. Brown, E.R, and Cooley, L.A., “Designing Stone Matrix Asphalt Mixtures, Volume III,
Summary of Research Results, Final Report” NCHRP 9-8/3, Transportation Research Board,
July 1998.
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West and James 9
LIST OF TABLES
TABLE 1. Materials Used in the SMA Mix Designs
TABLE 2. Physical Characteristics of the Mineral Fillers
TABLE 3. Mix Design Results
TABLE 4. Results of the SMA Mixtures at the Same Asphalt Content, Draindown Results
TABLE 5. Results of Moisture Damage Susceptibility Tests Using AASHTO T283
TABLE 6. Results of AASHTO T283 Test on the LKD with the High Available Lime Content
TABLE 7 Effect of Extended Soak Time on Conditioned Tensile Strengths
TABLE 8. Results of the Hamburg WTD Tests
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TABLE 1. Materials Used in the SMA Mix Designs
Material Type Source Percent
Aggregates Granite
Vulcan Materials Co., 93.0%
(LA abrasion =
36%)
Columbus Quarry
Mineral A. Rock Dust Georgia Marble Co. 7.0%
Fillers B. Lime Kiln Carmeuse Natural 7.0%
Dust
Chemicals
Asphalt PG 67-22 Ergon *
Stabilizing
Fiber
Cellulose Interfibe 0.3%
* determined by the mix design procedure
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TABLE 2. Physical Characteristics of the Mineral Fillers
Characteristic LKD Rock Dust
Percent of Distribution Particle Size Particle Size
< 90% 49.1 µm 44.7 µm
< 75% 29.2 µm 29.6 µm
< 50% 14.8 µm 15.0 µm
< 25% 7.3 µm 5.8 µm
< 10% 3.4 µm 2.2 µm
Apparent Specific
Gravity
2.622 2.708
Rigden Voids (%) 45.9 37.8
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TABLE 3. Mix Design Results
Property SMA Criteria 1 Gradation (% Passing)
LKD SMA Rock Dust
SMA
12.5 mm
90 – 100 96
96
9.5 mm
26 – 78 36
36
4.75 mm
20 – 28 24
24
2.36 mm
16 – 24 22
22
1.18 mm
13 - 21 19
19
0.60 mm
12 - 18 16
16
0.30 mm
12 - 15 14
14
0.15 mm
12
12
0.075 mm
8.0 – 11.0 9.2
9.2
Optimum Asphalt
Content
6.0% min. 6.4% 6.6%
Air Void Content 4.0% 4.0% 4.0%
VMA 17.0% min. 17.1% 17.0%
VCAmix
< VCADRC
(40.1)
32.6 32.4
1
Based on NCHRP 9-8 recommendations, some criteria differ from AASHTO MP-8
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TABLE 4. Results of the SMA Mixtures at the Same Asphalt Content, Draindown Results
Property Criteria LKD SMA Rock Dust SMA
Asphalt Content - 6.5% 6.5%
Air Voids @
Ndes
-
3.9% 4.3%
Binder
Draindown
0.3% max.
0.01% @ 300º F
0.00% @ 327º F
0.03% @ 300º F
0.01% @ 327º F
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TABLE 5. Results of Moisture Damage Susceptibility Tests Using AASHTO T283
Property Criteria LKD SMA
Rock Dust
SMA
Avg. Air Voids % 6 ± 1.0 5.9 5.9
Avg. Saturation % 70-80 77 73
Avg. Conditioned Strength,
psi
- 79.0 78.0
Avg. Unconditioned
Strength, psi
- 92.7 94.6
Tensile Strength Ratio 0.70 min. 0.85 0.83
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TABLE 6. Results of AASHTO T283 Test on the LKD with the High Available Lime Content
Property Criteria XLKD SMA
Avg. Air Voids % 6 ± 1.0 6.2
Avg. Saturation % 70-80 78
Avg. Conditioned Strength,
- 24.6
psi
Avg. Unconditioned
Strength, psi
- 98.8
Tensile Strength Ratio 0.70 min. 0.25
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TABLE 7 Effect of Extended Soak Time on Conditioned Tensile Strengths
Conditioned Strengths, psi
Hot Water (60
C) Soak Time LKD SMA
Rock Dust
SMA
24 88.5 87.3
48 77.1 67.6
96 92.4 76.9
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TABLE 8. Results of the Hamburg WTD Tests.
LKD SMA Rock Dust SMA
Stripping
Stripping
Inflection
Inflection
Air Voids Point Sample Air Voids Point
Sample # (%) (cycles) # (%) (cycles)
LKD 4 6.5 7000 RD 2 6.6 1060
LKD 5 7.6 1270 RD 3 5.9 4500
LKD 7 5.7 2930 RD 4 6.3 8000
LKD 7a 6.8 5250 RD 14 5.4 1700
LKD 8 7.8 3200
Average 6.9 3930 Average 6.1 3815
Std. Dev. 0.9 2223
Std.
Dev.
0.5 3145
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LIST OF FIGURES
FIGURE 1. Effect of Freeze-Thaw Cycles on Tensile Strengths
FIGURE 2. Photograph Showing Discoloration of LKD SMA Specimen (on right)
FIGURE 3. Comparison of Height Changes for Samples Soaked in CBR Molds.
FIGURE 4. Typical Hamburg WTD Result Showing Rutting Rate and Stripping Inflection Point.
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Tensile Strength (psi)
100
95
90
85
80
75
70
65
60
55
50
LKD SMA
Rock Dust SMA
0 1 2 5
Freeze-Thaw Cycles
FIGURE 1. Effect of Freeze-Thaw Cycles on Tensile Strengths
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FIGURE 2. Photograph Showing Discoloration of LKD SMA Specimen (on right)
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Height Increase (mm)
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
Rock Dust SMA
LKD SMA
0.00
0 20 40 60 80
Time (hours)
100 120 140 160
FIGURE 3. Comparison of Height Changes for Samples Soaked in CBR Molds.
TRB 2006 Annual Meeting CD-ROM Original paper submittal – not revised by author.
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West and James 22
Rut Depth (mm)
40.00
35.00
30.00
25.00
20.00
15.00
10.00
5.00
Rutting Rate (mm/cycle)
Stripping Inflection Point, SIP (cycles)
0.00
0 2000 4000 6000
Cycles
8000 10000 12000
FIGURE 4. Typical Hamburg WTD Result Showing Rutting Rate and Stripping Inflection Point.
TRB 2006 Annual Meeting CD-ROM Original paper submittal – not revised by author.
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