National Cooperative Highway Research Program

NCHRP Project 20-07/Task …

Project Title: Development of a Framework for Balanced Asphalt Mixture Design and Gap Analysis

Fiscal Year: 2016

Contract Time: 12 months

Funds: $100,000

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RFP Close Date (proposal due date):

Proposals must be submitted by email to:

BACKGROUND

In September 2015, the FHWA Expert Task Group on Asphalt Mixture and Construction formed a Task Force on Balanced Mixture Design (BMD) to move forward changes in the way asphalt mixtures are formulated. The task group has defined BMD as “Asphalt mixture design using performance tests on appropriately conditioned specimens that address multiple modes of distress taking into consideration mixture aging, traffic, climate and location within the pavement structure.” The objective of BMD is to design asphalt mixtures for performance using a rational approach instead of relying on strictly volumetric guidelines. The Task Force has identified three types of approaches used for a Balanced Mixture Design:

1. Volumetric Design with Performance Verification. Volumetric design is done as the first step and then performance properties are confirmed. Both the volumetric properties and performance test results must meet the established criteria. If enhancements are required to improve performance then different materials or proportions (aggregate, asphalt binder) would be used to enhance the performance properties. This is the most common approach currently in use by SHAs.

2. Performance-modified Volumetric Design. Volumetric design is done as a preliminary step and then adjustments are made to either component properties (such as asphalt binder grade or properties of the aggregates) or volumetric properties (such as air voids and VMA.) The final design is not required to meet the volumetric criteria for Superpave, only the performance test criteria. 3. Performance Design. Mixture design is based on performance analysis with limited or no requirement for volumetric properties. Minimum requirements might be set for asphalt binder and/or aggregate properties. Otherwise, component properties would be selected to meet the performance test criteria. Air voids and VMA might be non- mandatory suggestions. This approach has not been used by SHAs at this time, but could be a viable option.

Some states have started to adopt these various levels of BMD. The Task Force identified Illinois, Louisiana, New Jersey, Texas, and Wisconsin as Approach 1 states. California is using Approach 2, and Rutgers University is proposing Approach 3 for New Jersey. However, a survey by the BMD Task Force revealed that overall there is a lack of understanding of the balanced mixture design concept (i.e., what performance tests work and what criteria should be used). There is a need to develop an AASHTO Recommended Practice for Balanced Mixture Design that presents alternate approaches for BMD that recognizes the need for flexibility based upon the users’ needs and capabilities.

OBJECTIVE

The work proposed in this Research Problem Statement will develop a framework or general outline of an approach for states to devise and implement balanced asphalt mix design procedures in order to incorporate performance testing and criteria. This framework would need to be general enough to encompass different testing procedures and criteria. It is acknowledged that there are a number of gaps that would be necessary to develop a more detailed standard practice.

WORK TASKS

The NCHRP is seeking the insights of proposers on how best to achieve the research objective. Proposers are expected to describe a research plan that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposer’s current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meet the research objective.

This research project will result in the: 1. survey of all state highway agencies (SHAs) to determine the use and status of BMD practices with more detailed interviews of those that are more advanced in implementation, 2. review of literature for the development and state-of-the-practice for performance testing, 3. develop a practice that is a framework for BMD for implementation of performance testing in the design of asphalt mixtures, 4. develop research problem statements with funding needs based on gaps identified for development of a more detailed standard practice for BMD, and 5. prepare a final report that documents results, summarizes findings, draws conclusions, and presents the (a) proposed practice and (b) research problem statements based on identified gaps with funding needs and a recommended plan for submittal.

It is envisioned that gaps be identified for future NCHRP research projects. If there are a significant number of research problem statements developed, a plan for submitting the research problem statements should be developed. The plan would include an estimate of the appropriate order and timing for each of the research problem statements.

Examples of gaps include the relationship of tests to pavement performance which could include construction of demonstration projects; suitability for use with new and/or unknown materials; testing issues including precision and bias and ruggedness; failure criteria for rutting and cracking tests appropriate for different regions, material types and conditions; use in field acceptance including sensitivity to changes in key properties; the role and use off volumetric properties; the use of cores; and others.

CONTACT PERSON Tim Aschenbrener, P.E. FHWA Office of Infrastructure Senior Asphalt Pavement Engineer 12300 W. Dakota Avenue, Suite 280 Lakewood, CO 80228 Office: (720) 963-3247 [email protected]

SUBMITTED BY

Ross “Oak” Metcalfe

SPECIAL NOTES

A. Proposals should include a task-by-task breakdown of labor hours for each staff member as shown in Figure 4 in the brochure, “Information and Instructions for Preparing Proposals” (http://onlinepubs.trb.org/onlinepubls/crp/docs/ProposalPrep.pdf). Proposals should also include a breakdown of all costs (e.g., wages, indirect costs, travel, materials, and total) for each task using Figures 5 and 6 in the brochure.

B. Monthly and Quarterly progress reports will be required.

Others to be determined…