Development of Mechanistic-Empirical Pavement Design Criteria for Pavement Rehabilitation using Full-Depth Reclamation
In-place full-depth reclamation (FDR) is a proven cost-effective and environmentally sustainable strategy for rehabilitating old, distressed asphalt concrete pavements. It reuses existing materials and has minimal impact on traffic. The recycled materials can be left unstabilized, or stabilized during the recycling process with foamed asphalt, asphalt emulsion, cement, alone or in combination. Although the approach has been used in the United States for more than 15 years, most designs have been empirical and largely based on the experience of a few practitioners. Current mechanistic-empirical design procedures do not have any parameters for FDR layers, nor has any significant testing been done to develop them on a national scale. Foamed asphalt in combination with portland cement is a commonly used stabilizer in FDR. When used individually for stabilization of marginal materials or in full-depth reclamation (FDR) projects, each has both advantages and limitations. Asphalt is generally not appropriate for materials with high fines contents or with plasticity. Portland cement can result in very stiff and brittle layers that are prone to shrinkage, and susceptible to reflected cracking. Observations of projects where foamed asphalt has been used in combination with cement indicate that better performance can be obtained compared to that when the stabilizers are used individually. Laboratory strength tests and field stiffness tests indicate a strong, but relatively flexible material with improved moisture resistance. Electron microscope studies indicate a different stabilization mechanism compared to materials treated with the individual stabilizers. In light of these observed benefits, guidance is required on the long-term behavior of layers stabilized with this combination to ensure that appropriate criteria are used when undertaking a mechanistic-empirical pavement design. Designers currently model these layers as either asphalt or cement, neither of which is appropriate, leading to inaccurate and/or inappropriate pavement designs. Guidance is also required on determining optimal ratios of the two stabilizers to ensure optimum performance.
The main objective of
this research project is to develop mechanistic-empirical design criteria for
pavement rehabilitation using full-depth reclamation. The project will also develop guidance on the
use of asphalt (foamed or emulsion) in combination with portland cement for
stabilization of marginal materials and/or in full-depth reclamation projects.
Key issues include the development of performance models/factors that can be
incorporated into current mechanistic-empirical pavement design procedures and
development of laboratory testing procedures that can be used to select the
most appropriate combinations of asphalt and portland cement stabilizers.
Meeting the proposed
objectives will be of great help to road agencies that have extensive networks
requiring upgrading or rehabilitation, and who require the best possible
performance from stabilized layers. The development of mechanistic-empirical
pavement design functions specific to layers and pavement structures
rehabilitated by in-place full-depth reclamation stabilized with asphalt,
cement or an appropriate combination of them will allow agencies to design
appropriate, cost-effective structures without having to make unsubstantiated
assumptions about expected performance. Guidance on the selection of
appropriate stabilizer combinations and ratios, mix design testing, performance
testing, and specifications will assist practitioners on making informed decisions
and potentially reduce the cost of pavement rehabilitation projects.
design and construction methods currently specified by highway agencies are
based on generic recommendations developed by the Asphalt Recycling and
Reclaiming Association (ARRA) and the recommendations of contractors and
stabilizer suppliers. They tend to be based more on empirical observations than
on mechanistic testing and modeling. Several state agencies have funded
state-specific projects on the topic. It would be desirable to accumulate the
general knowledge in one source to ensure a uniform process throughout the
United States, and to ensure that the guidance is applicable to all types of
roads (local, county, state, federal lands) and not only the typically higher
volume inter-urban roads managed by state agencies.
Tasks associated with this project should
include, but not be limited to:
Task 1. Literature review on
research conducted on the topic as well as establishment of a project database of
highway sections rehabilitated using full-depth reclamation with and without stabilization.
Contact transportation agencies, private contractors and trade organizations as
appropriate to augment this assessment.
Task 2. Based on the results of Task 1, develop and implement a
laboratory testing framework that compares the performance of materials treated
with the individual stabilizers and combinations of them. Testing should focus
on mechanistic properties and long-term performance. Electron microscope and
other appropriate scanning procedures should be used to understand the
micro-mechanical stabilization mechanisms of the different treatments and their
relationship to observed performance.
Task 3. Using the results obtained in Task 2, develop a framework for
full-scale testing to validate the laboratory test results. Accelerated load
testing on instrumented test tracks in combination with testing on in-service
pavements should be used to obtain life-cycle performance criteria that can be
used to prepare mechanistic design functions that will allow practitioners to
confidently design pavements with a combination of stabilizers.
Task 4. Prepare a guideline document on the mechanistic-empirical design
of rehabilitation projects using full-depth reclamation. This guideline will
include stabilizer selection guidelines based on subgrade, drainage, material,
traffic, and climate conditions, mix design testing, performance testing, and
suggested specification language.
Task 5. Prepare supporting documentation for incorporating the design approach
and design functions into the Darwin
and other mechanistic empirical pavement design procedures.
It is anticipated
that AASHTO and the Federal Highway Administration will take ownership of the
It is anticipated that AASHTO and the Federal Highway Administration will take ownership of the planned deliverables.
|Sponsoring Committee:||AFS90, Chemical, Mechanical, and Asphalt Stabilization
|Research Period:||24 - 36 months|
|RNS Developer:||David Jones|
|Index Terms:||Full-depth reclamation, Cost effectiveness, Rehabilitation (Maintenance), United States, Mechanistic-empirical design, Pavement design, Foamed asphalt, Portland cement, Waterproofing, |
|Cosponsoring Committees:||AFD70, Pavement Rehabilitation; AKC60, Asphalt Pavement Construction and Rehabilitation|
Maintenance and Preservation