Clearing the way: a national center is providing research to overcome barriers to using recycled aggregates and materials.

The Recycled Materials Resource Center (RMRC), Durham, N.H., is a national center that promotes the appropriate use of recycled materials in the highway environment. The RMRC has a particular focus on the long-term physical and environmental performance of these materials.

In this sense, recycled materials include traditional waste materials, secondary use materials, industrial by-product materials and reclaimed highway construction materials. The center is unique in that its mission is to overcome barriers to the responsible use of recycled materials through a combination of products-based research and outreach activities.

Formally established in 1998 through a cooperative agreement between the Federal Highway Administration (FHWA) and the University of New Hampshire (UNH), the Center is located within the Environmental Research Group at UNH. Throughout the past six years the RMRC has sponsored several conferences and workshops and has supported more than 30 research projects. The over-arching goal of all the projects has been the development of specifications, testing protocols and other guidance documents that support the center's mission.

The following project summaries describe some of the projects relevant to the C&D industry. For a more complete description of all the projects, go to the RMRC's Web site at www.rmrc.unh.edu.

CONCRETE SUPPORT

Using Lithium to Mitigate ASR in RCA Concrete: This research is an extension of work completed earlier during RMRC Project 1: "Mitigating Alkali Silicate Reaction in Recycled Concrete." A tremendous quantity of infrastructure Portland Cement Concrete (PCC) is nearing the end of its useful life in the United States, and much of this concrete has the potential to be used as recycled concrete aggregate (RCA). However, a significant amount of this concrete has been severely affected by alkali silicate reaction (ASR).

Some portions of the country have plentiful supplies of non-reactive aggregates for use in rebuilding. However, many areas of the country do not have the benefit of non-reactive aggregates and must contend with the potential for ASR on an everyday basis. The goal of this project is to provide guidance to those states that want to use RCA that contains potentially reactive aggregate. At least one state highway agency (SHA) has established a policy of mandatory recycling of any construction material within the zone of the construction contract. This may eventually be a requirement on all SHA projects in light of limited landfill space and the effect of current environmental trends, emphasizing the need for guidance on how to use RCA.

Lithium nitrate is very effective at controlling ASR in new concrete, but, so far, a clear understanding of the mitigation effect of an externally applied lithium nitrate solution has not been well established. The main questions surrounding this work are how often to apply the solution, how to measure the penetration depth and how to evaluate the mitigation results and determine when it is too early or too late for an application to be cost effective.

Evaluation of Tests for Recycled Material Aggregates for Use in Unbound Applications: Many recycled materials are available in quantities sufficient for use as unbound aggregate in base course or fill applications. The recent adoption of AASHTO specifications on glass cullet (M-318-01) and reclaimed PCC (M-319-02) for granular base course is evidence of the widespread support for recycled material aggregates.

However, barriers to the widespread use of such materials remain, and one is a lack of research on the basic physical and mechanical properties of recycled material aggregates. The need for a review of testing procedures is required because some recycled aggregates may not perform well using traditional characterization procedures, even though the aggregate performs well in the field.

This project seeks to help overcome the barriers to widespread use of recycled materials as an aggregate by pursuing a research effort that focuses on evaluating potential aggregate materials other than reclaimed hot mix asphalt (HMA) and Portland cement concrete (PCC) pavements. Because NCHRP Project 4-31 will be addressing the use of aggregates from reclaimed HMA and PCC pavements, it will focus on recycled materials such as glass culler, steel slag and construction/demolition (C&D) aggregates.

Crushed concrete is available from C&D projects and PCC pavements; so crushed concrete will be considered even though the focus of this project is on materials other than reclaimed HMA and PCC pavements. Locally available natural aggregates will also be tested as controls for quality assurance. During the initial phase of this project, it became evident that there were questions about the appropriate compaction of recycled materials and the relevance of traditional methods, such as the Modified Proctor and vibratory table tests.

Development of a Risk Analysis Framework for Beneficial Use of Secondary Materials: The overall goal of this research project was to further the understanding of the leaching and transport of contaminants from pavement materials and to provide a tool for regulators to evaluate potential groundwater contamination from the use of virgin and secondary materials in road construction.

To this end, a new probabilistic framework was introduced which provides structured guidance for selecting the appropriate model; incorporating uncertainty, variability and expert opinion; and interpreting results for decision making. In addition to the framework, specific contributions were made in pavement, embankment hydrology, reactive transport, Bayesian statistics, and the aqueous geochemistry of leaching under local equilibrium conditions.

AIDING ASPHALT RECYCLING

Properties of Asphalt Mixtures Containing RAP: One goal of the RMRC is to support research that leads to products with real-world applications. This project is a good example of such research because it is being done in cooperation with NH DOT to investigate some of the basic questions regarding the incorporation of recycled asphalt pavement (RAP) into new asphalt, while at the same time developing mix designs that NH DOT can actually use.

Currently, NH DOT allows 35-50 percent RAP in base courses and up to 15 percent RAP in surface courses. However, it is still not clear as to how RAP changes the mechanistic and performance properties of the mix design. This is because of the complex interaction of the aged binder in the RAP with the new binder in the asphalt and the aggregate properties of RAP compared to aggregate in the virgin mix. This research focuses on understanding these issues.

Development and Preparation of Specifications for Recycled Materials in Transportation Applications: This project addresses the lack of appropriate specifications for using recycled material, preventing the widespread use of these materials in the highway construction environment.

Fifteen state DOTs agreed to participate to develop common specifications for a several material/application combinations. To date, two specifications for glass cullet and for crushed concrete in base layers have been accepted by AASHTO. Recommendations to AASHTO regarding coal fly ash in embankments, crushed concrete in PCC and shingles in hot mix asphalt are under review.

Development of a Rational and Practical Mix Design System for Full Depth Reclamation (FDR): Full depth reclamation is an asphalt pavement recycling technique in which the asphalt layer and part of the unbound sub-layer are processed in place and then put down as a stabilized base course.

There is significant nationwide interest in this technology, but questions remain about mix design optimization. In response, the expected end products of this project include a full-depth reclamation (FDR) mix design specification to AASHTO (via the Maine DOT). A full-depth reclamation Technology Ready for Implementation report has already been accept by AASHTO (again via Maine DOT).

Overcoming Barriers to Asphalt Shingle Recycling (Phase Three): This is the final phase of a project that continues more than 10 years of research and development in Minnesota on the recycling of shingle scrap. Phase Three focuses on field-testing, market development and technology transfer of tear-off shingle scrap (TOSS) recycling.

The end-use road construction applications to be demonstrated include use of processed TOSS as a dust control supplement, an unbound aggregate supplement as base and a 5-percent blend into hot-mix asphalt (HMA). One of the first products will be a report on lab results from a standardized sampling and testing protocol intended to measure if any asbestos is present in random samples of TOSS. (Editor's Note: This work will be presented at the 2005 ConExpo-Con/Agg show in Las Vegas.)

BREAKING BARRIERS

A Life Cycle Analysis Model and Decision-Support Tool for Selected Recycled Vs. Virgin Materials for Highway Applications: This project came about because even though the success of the RMRC shows there is support for recycled materials, significant barriers to recycled materials use in the highway environment still exist. One such barrier is a lack of data and guidance about determining the true costs associated with using recycled or even virgin materials.

When considering recycled materials, designers and managers must often choose materials from a long list of candidates and then compare the economic, environmental and engineering behavior of recycled versus virgin materials. This selection process can be very confusing and time consuming.

In response, this project developed a life cycle cost analysis (LCCA) framework and computer based decision tool that uses environmental parameters to assist decision-makers in evaluating the use of recycled materials. This software, named PALATE, is unique in that it combines traditional economics based tools with tools to quantify short and long term physical and environmental effects as well.

The author is the outreach director of the Recycled MateriaLs REsource Center at the University of New Hampshire. He can be reached at [phone] or at [e-mail].