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!