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

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 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  Five virgin aggregates  Three RAP contents (20%, 30% and 40%)  Two sources ● Test: Texas Overlay Test and Semi-Circular Bending Test

Aggregate Blending SR-12.5A (with RAP) 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 10 sec/cycles Fixed opening displacement 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 0.05 inch/min on 3 replicates Peak Load Average of the Peak Failure load from Static tests recorded Cyclic Cyclic haversine load 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)

Repetitive SCB Test Shiling RAP

Statistical Analysis Comparison of Means SR-12.5A (Shilling RAP) RAP% Asphalt% Groups*aaa SR-12.5A (Konza RAP) RAP% Asphalt% Groups*aab SR-12.5A (Shilling RAP) RAP% Asphalt% Groups*abc SR-12.5A (Konza RAP) RAP% Asphalt% Groups*abb *Mix types not connected by same letter have statistical significant difference R-SCB TestOT 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!