SWUTC Research Project Description
Search for a Test for Fracture Potential of Asphalt Mixes
Project Number: 0-6607
Principal Investigator:
Tom Scullion
(979) 845-9913
P.I. Affiliation: Texas A&M University
Project Monitor:
Project Status: Active
Date Started: 9/1/09
Estimation Completion Date: 8/31/12
Estimated Cost – Current Fiscal: $182,643
Estimated Cost – Total Planned: $182,643
Project Summary
Project Abstract:
The incorporation of the Hamburg Wheel Tracking test in the TxDOT mix-design specifications has resulted in HMA mixes that exhibit resistance to rutting, but in many cases, lack the optimum resistance to fracture and cracking. Field evidence indicates that most of Texas’ HMA pavements are prone to cracking with the occurrence of other premature failures related to cracking. As a means to address this issue, TxDOT currently uses and has implemented the Overlay Tester (OT) to evaluate the cracking susceptibility and resistance to reflective cracking of HMA mixes. While, the OT has fairly been satisfactory with SMA and Crack Attenuating Mixture (CAM) mixes, performance has been relatively poor with most conventional dense-grade HMA mixes such as Type A, B, C and D (Items 340/341), which makes up about 75% of all the HMA mixes used in Texas. This is partly attributed to the severity of the OT which results in high variability of the OT on dense graded mixes. A laboratory mixture test to characterize the cracking susceptibility of HMA mixes is thus greatly needed for all the Texas HMA mix types. As a minimum, such a test protocol must have the following characteristic features:
- Applicability for routine HMA screening and not necessarily performance prediction such as fatigue life.
- Practical and easily implementable by TxDOT.
- Easy sample preparation with potential to test both lab-prepared and field cores.
- Reasonable test duration of nor more than one day.
- Acceptable level of variation and test reliability.
Project Objectives:
In order to address the objective of this project, various crack tests will be evaluated including the following: Overlay Tester, direct-tension test, indirect-tension test, semi-circular bending test, bending beam, and the C(T) ASTM 7313 (b). Expected deliverables from this study will include recommendations for a practical and reliable test for routine crack evaluation of HMA mixes with acceptable level of variability. A preliminary test protocol along with the laboratory test procedures and mix screening criteria will be submitted to TxDOT.
Task Descriptions:
Task 1: Literature Search
- Subtask 1.1: Literature Review
- Subtask 1.2: Project Kick-Off Meeting
Task 2: Comprehensive Sensitivity Evaluation and Improvement to the Overlay Test Procedure
- Subtask 2.1: Documentation of Problems and Concerns about OT Procedure through Liaison with CST (Cedar Park), TxDOT Labs, and ShedWorks Inc.
- Subtask 2.2: Sensitivity Evaluation of all Critical Steps in OT Test Procedure
- Subtask 2.3: Evaluation of OT data Analysis Procedure and Failure Criteria
- Subtask 2.4: Updates to the Tex 248-F Test Method
- Subtask 2.5: Round Robin Tests between TTI and CST
- Subtask 2.6: Upgrade all the Remaining OT Machines in Texas
- Subtask 2.7: Evaluation of More Advanced OT Data Analysis and Evaluation Procedures (The J-Integral and Pseudo STrain Energy Method)
- Subtask 2.8: Training Workshop in Austin
Task 3: Parallel Testing of Split Samples from TxDOT Projects
Task 4: Development of Test Procedures for Alternative Cracking Tests
Task 5: Comprehensive Laboratory Evaluations of Potential Repeated Load Fracture Tests
- Subtask 5.1: Comparative Evaluations of Test Repeatability and Variability
- Subtask 5.2: Sensitivity and Statistical Evaluations of the Crack Tests
- Subtask 5.3: Periodic AV Measurements with TTI’s X-Ray CT Scanner
Task 6: Correlation of Lab Test Results with Field Test Sections
Task 7: Recommended Test Procedures and Specifications
Task 8: Case Study: Demonstration of How to Improve Asphalt Mixture Design
Task 9: Prepare Reports
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