Optimizing Flexible Pavement Performance Based on Aggregate Physical Properties
Studies over the last four decades have identified and demonstrated the effects of aggregate morphological properties (particularly shape, size distribution, angularity and texture) on the mechanical properties of hot mix asphalt (HMA). Other studies have focused on aggregate test methods; most notably, perhaps, NCHRP 4-30A recommended test methods to accurately and rapidly measure aggregate shape, texture and angularity.
None of these studies, however, have clearly established relationships between the aggregate properties and the ultimate pavement performance. Therefore, they have not provided methods to optimize aggregate properties at the design stage to improve that performance. Research is needed to relate aggregate properties to flexible pavement performance and adequately account for the pertinent properties in design.
The properties of shape, texture and angularity can now be measured with automated techniques that offer higher precision than conventional methods. In addition to these properties, other factors to consider include aggregate point and mass strength as well as the effects of blending. Pavement performance properties to be considered and optimized include durability, resistance to loads, frictional properties, etc. The current (and likely continuing) state of the economy necessitates finding more economical pavement designs, which will likely require the use of more locally available aggregates of the beneficiation of marginal materials. The impacts on pavement performance of using these materials, however, must be understood to adequately quantify their effects on the pavement’s service life and life cycle costs.
The objective of this work is to develop quantitative relationships between aggregate and asphalt cement (AC) properties measured in the laboratory with field performance of flexible pavements. Advanced analytical methods, including modeling and simulation, should be employed in establishing these relationships. Then, develop methods to optimize available aggregate selection for HMA designs based on the physical properties of the aggregates such that the pavement performance is maintained or improved while the economics are optimized.
Deliverables will provide a process to use of aggregates with wide ranges of physical characteristics in the design of HMA. The following tasks are considered necessary to achieve these objectives:
1. Literature Search: Review and summarize existing literature on HMA aggregate properties, HMA performance, blending of aggregates, and existing relationships between aggregate morphological characteristics, laboratory AC properties, and HMA performance.
2. Aggregate Characterization: Identify aggregate properties and categorize the test methods to measure at least shape, texture, angularity, point and mass strength, absorption, and hardness.
3. AC Characterization: Identify AC properties used in HMA design and pavement performance evaluations.
4. HMA Characterization: Identify test methods and procedures to assess the performance of aggregates in HMA and in the field where performance has been closely monitored, such as LTPP test sections; accelerated field test sections such as MnROAD, WesTrack and NCAT; and other test sections.
5. Experimental Design: Propose a Phase II research approach for an HMA performance optimization process. Obtain approval from the project panel before initiating Phase II.
6. Perform aggregate characterizations to obtain relevant aggregate morphological and other characteristics of aggregates used in field test sections. Identify and characterize other aggregates with a range of properties, including aggregate blends including marginal materials with higher quality aggregates to meet combined properties.
7. Design HMA mixtures according to the current nationally accepted requirements for the design of pavement layers using the aggregates from task 5.
8. Measure the performance of aggregate blends in HMA using laboratory performance tests and accelerated loading tests.
9. Adjust the aggregate blends and mix designs based on aggregate properties and demonstrate the influence of these adjustments on performance.
10. Evaluate the relationship of field performance and laboratory test results to aggregate properties.
11. Develop advanced analytical methods to establish the relationships and validate them statistically.
12. Recommend aggregate tests and properties that correlate best with field performance.
13. Develop new aggregate tests as needed to complete the correlation of aggregate characteristics with flexible pavement performance.
14. Develop guidelines for adaptable design methods for HMA pavement layers, including consideration of aggregate properties and aggregate blending.
15. Recommend performance-based limits for pertinent aggregate properties.
16. Develop a plan for future field validation of the recommended tests, design methods and performance limits as well as an implementation plan to move the deliverables into practice.
17. Produce and publish a final report documenting the results of this research.
III. Key Words and Subjects
Aggregates, Hot Mix Asphalt, Optimization, Pavement Design, Performance Evaluations
Highways, Construction, Design, Materials, Pavements
IV. Related Work
V. Urgency and Priority
Aggregates constitute roughly 90% of the volume of HMA mixtures and their properties have a huge impact on the performance of the mixture and the pavement in which it is placed. Recent work provides improved tests to characterize aggregate properties, but the relationship to pavement performance has not yet been established. Understanding this relationship is critical to optimizing aggregates for the particular application in which they will be used and thereby appropriately optimizing the HMA mixture.
VI. Cost and Time
Estimated Funding: $1,000,000 ($75,000 for Phase 1, $925,000 for Phase 2)
Estimated Period of Performance: 48 months (9 months for Phase 1, 39 months for Phase 2)
VII. User Community
Federal, state, and local transportation agencies are the users who will primarily benefit from this work.
This research will have immediate impact on reducing construction costs and improving pavement performance. It will also allow more use of locally available or previously-considered marginal materials, which will help to conserve existing resources of high-quality aggregate. The recommendations from this project could be implemented rapidly by specifying agencies, designers, material suppliers and contractors.
This understanding of the relation of the aggregate physical properties and implementing the recommended optimization will result in an immediate improvement in HMA performance.
X. Committee Information
Sponsoring Committee: AFP70, Mineral Aggregates
Co-sponsoring Committees: none
Contact Information: AFP70 Research Needs Statements (RNS) Subcommittee Members: Roger Surdahl, FHWA; Rick Meininger, FHWA; and Scott Seiter, ODOT. AFP70 Committee Members or Friends: Rebecca McDaniel, Purdue University.
Date Drafted: 04/25/2009
Date Initially Posted: 06/02/2009
Date Updated: 02/21/2012
Date Reposted: 03/01/2012
AFP70 rates this RNS as priority #3 out of 6 current statements.
|Sponsoring Committee:||AFP70, Mineral Aggregates
|Source Info:||Committee Members|
|Index Terms:||Flexible pavements, Service life, Life cycle costing, Asphalt concrete, Aggregates, Hot mix paving mixtures, Pavement performance, Texture, Pavement design, Mix design, Field tests, Optimization, |