Materials

As virgin materials become scarce and the volume of by-product materials generated in our society and the cost of disposal continue to increase, there is increased pressure and incentive to recover and recycle these materials for use in secondary applications. Because the construction of highways requires large volumes of materials, transportation agencies have become participants in these recycling efforts. From a highway engineering perspective, recovered materials should be used in such a manner that the expected performance of the highway will not be compromised. By-product materials, however, differ vastly in their types and properties and, as a result, in the highway applications for which they may be suited. Experience and knowledge regarding the use of these materials vary from material to material as well as from state to state. To recover these materials for potential use, engineers, researchers, generators, and regulators need to be aware of the materials' properties, how they can be used, and the limitations associated with their use. 

The primary purpose of this guidance document is to assist those who have an interest in using or increasing their understanding of the types of by-product materials that may be recovered and used in highway construction applications. It is intended to provide the potential user or reviewer with sufficient information on each material included in this document so that he or she will have an understanding of the nature of the material, where other information may be obtained, and what issues need to be evaluated when considering its use. It is also intended to provide the reader with general guidance on engineering evaluation requirements, environmental issues, and economic considerations for determining the suitability of using recovered materials in highway applications. 

Because of the ongoing development and publication of new information regarding the use of recovered materials in highway applications, this site may be updated periodically. A 2007 update includes new information for the following materials and their applications: coal bottom ash/boiler slag, coal fly ash, FGD scrubber material, foundry sand, reclaimed asphalt pavement, recovered concrete material, and roofing shingle scrap. The rest of the information on materials is current as of 1995.

These guidelines cover the use of byproduct materials in six major highway construction applications: 

1. Asphalt Concrete

2. Portland Cement Concrete

3. Granular Base

4. Embankment or Fill

5. Stabilized Base

6. Flowable Fill

In each of these primary application categories, there is at least one possible material use, and in some cases, there are several potential uses. This document includes guidelines for 19 by-product materials. The matrix below provides an easy way to navigate the material-application combinations. The materials do not represent the entire population of materials that have potential use in highway construction applications. These materials were selected based on the amount of material generated as well as whether adequate data were available to prepare a description of the physical and chemical properties of the material and to describe the design requirements and performance records for one or more specific applications. The omission of a particular material-application match in these guidelines is not to be construed as a prohibition against its use; rather, omission merely indicates that the authors felt that either the material-application combination was inappropriate or that insufficient information was available to provide a useful guideline.

The major portion of this document presents, for each of the 19 materials, a description of the material and user guidelines that includes the applications listed in the matrix. In addition to material-specific guidelines, several chapters of the report are devoted to recommended evaluation procedures for assessing whether a material is suitable for use in a designated application and to the environmental and cost issues that need to be considered when evaluating the use of by-product materials in highway construction. Finally, summary descriptions of the six highway construction applications are presented to assist those readers who are interested in additional information relative to their design objectives and material uses.