Evaluation of Cracking Resistance of Superpave Mixtures Using Texas
Overlay TestSyeda Rubaiyat AzizMustaque Hossain
Greg Schieber
Department of Civil EngineeringKansas State University
Outline ● Background● Objective● Materials & Test Method● Laboratory Testing● Results● Conclusions & Recommendations● Acknowledgements
2
Research Background● About 94% of paved road in the United States is Hot-Mix
Asphalt (HMA)
● Annual HMA production is about 500-550 million tons
● Reasons for increased use of reclaimed asphalt pavement (RAP):
Rise in oil price, emphasis on sustainability, limited virgin aggregate availability
● High RAP content sometimes leads to drier mix, prone to early cracking
Objective● Investigate cracking resistance of Superpave mixtures
with varying RAP content
● Investigate effect of RAP source on cracking resistance
Materials & Test Method● Materials: Superpave 12.5-mm NMAS mixture with
PG 70-28
Five virgin aggregates
Three RAP contents (20%, 30% and 40%)
Two sources
● Test: Texas Overlay Test and Semi-Circular Bending Test
Aggregate BlendingSR-12.5A (with RAP)
0
20
40
60
80
100
Sieve Size (mm)
% Pa
ssin
g
0.45 Power Gradation Chart for SR-12.5A (RAP Source 1)
20%30%40%
0
20
40
60
80
100
Sieve Size (mm)
% Pa
ssin
g
0.45 Power Gradation Chart for SR-12.5A (RAP Source 2)
20%30%40%
First RAP source(Shiling)
Second RAP source(Konza)
Texas Overlay Test (TEX-248-F)● Simulates opening or closing of joints, which
accelerates crack initiation and propagation● Controlled displacement mode● Test performed at 25° C
Texas Overlay Test (Cont…)
Courtesy: TTI manual Tex-248-F
• After cutting, air void is checked (7±1)%, then glued on base plates
• 3 replicates from each Mixture
Texas Overlay Test (Cont…)
Gluing• Attaching to base plates using
Epoxy glue• 8 hours curing
Placement• Placing in side OT jig • LVDT attached at
back
Test Input
• Cyclic triangular loading @ 10 sec/cycles
• Fixed opening displacement 0.025 inch
Termination• Load reduction to 93%
of initial load or 1000 cycles
Output• Initial load• % of load
reduction• No of OT
cycles of failure
Semi-circular Bending Test (SCB)● Half disc shaped (3’’ diameter, 2’’
thick)● Must satisfy 7±1 % air void ● Notched at bottom● Three point bending setup● Loaded in compression● Test temperature at 25° C● 3 Static & 12 Cyclic test specimens
for each mixture
SCB Test (Cont…)
s = 0.8 R
Static
• Static load applied @ 0.05 inch/min on 3 replicates
Peak Load
• Average of the Peak Failure load from Static tests recorded
Cyclic
• Cyclic haversine load applied @ 10 Hz frequency with no rest period
Cyclic Input
• 30%, 40%, 50% & 60% of Avg. Peak Static load given as inputs & 3 specimen tested for each
Output • Load, Duration and No. of Cycles to failure
2S
2R
S = 0.8 R
Results
Results (Overlay Test)
0100200300400500600700800900
1000
Source_RAP %_Asphalt %
Cycl
es R
esis
ted
Unti
l Fai
lure
Repetitive SCB Test
20 30 40 50 60 700
10000
20000
30000
40000
50000
60000
SCB Percent Load Relationship Curve (SR-12.5A)
20% RAP30% RAP40% RAP
Percentage of Maximum Static Load (%)
SCB
Load
Rep
etitio
ns to
Cra
ck F
ailu
re
20 30 40 50 60 700
10000
20000
30000
40000
50000
60000Konza RAPShiling RAP
Statistical AnalysisComparison of Means
SR-12.5A (Shilling RAP)
RAP% 40 30 20
Asphalt% 4.3 4.8 4.7
Groups* a a a
SR-12.5A (Konza RAP)
RAP% 30 20 40
Asphalt% 4.4 4.3 4.1
Groups* a a b
SR-12.5A (Shilling RAP)
RAP% 40 30 20
Asphalt% 4.3 4.8 4.7
Groups* a b c
SR-12.5A (Konza RAP)
RAP% 30 20 40
Asphalt% 4.4 4.3 4.1
Groups* a b b
*Mix types not connected by same letter have statistical significant difference
R-SCB Test OT Test
Conclusions● Based on the Texas Overlay test results:
Increase in RAP content reduces cracking resistance Overall, mixtures with first RAP source carried higher no. of OT cycles prior
to failure compared to second RAP source
● Based on SCB test results: Similar trend of results as OT tests were obtained 20% RAP performed well for first RAP source and 40% RAP performed well
for second RAP source
Recommendations
● Study more RAP sources ● Correlate cracking test results with actual field data
Acknowledgements
● This study has been sponsored by the Kansas Department of Transportation (KDOT)
Thank You!
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