Evaluation of Cracking Resistance of Superpave Mixtures Using Texas Overlay Test Syeda Rubaiyat Aziz Mustaque Hossain Greg Schieber Department of Civil Engineering Kansas State University
Feb 22, 2016
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!