Frequently Asked Questions


What kind of FDOT projects lend themselves to the use of a recycled/reused material?

  • The majority of transportation projects lend themselves to the use of recycled materials.

Are there any federal standards for recycled materials to be used in construction?

  • AASHTO Standards
    The American Association of State Highway Transportation Officials (AASHTO) has developed standards for using recycled industrial materials in cement and concrete. AASHTO M 295 and AASHTO M 302 are standard specifications for using fly ash and ground granulated blast furnace slag in cement and concrete in roadways.
  • Federal Highway Administration (FHWA) Recycled Materials Policy
    FHWA's policy statement is designed to advance the use of recycled materials in highway applications. The policy outlines the importance of re-using materials previously used in constructing the Nation's highway system, and calls upon the FHWA and State transportation departments to explicitly consider recycling as early as possible in the development of every project.

With regard to materials specifications, will FDOT accept other states' data?

  • When appropriate, the FDOT does accept other state's data. The typical process for the development of a specification is to first review the efforts of other states and AASHTO. The Department then determines the best fit for Florida's specific needs that will meet the material properties, climate and environmental requirements.  Where possible, the FDOT also uses national standards from AASHTO or ASTM directly.

What is the potential for recycled rubber, plastic, glass and perhaps ash to be used as a substitute for a virgin material or repurposed?

  • Rubber -- Rubber is used as a modifier for asphalt binder in pavements. In controlled amounts, rubber is beneficial in providing resistance to rutting and cracking.
  • Plastic -- Recycled plastic is used in a variety of products.  Economics in the industry heighten the use of recycled plastic products, which are often less costly than virgin materials. Therefore, the FDOT only needs to assure that the Department’s specifications do not restrict the use of plastics.  Ultimately, most materials manufactured from plastic that are used in highway applications have some recycled content. 
  • Glass -- Recycled glass is used for glass beads that provide reflectivity in highway striping.  Although it often has a limited supply when used in construction operations, crushed glass has been utilized as an aggregate for low volume pavements. Experience has shown, however, that crushed glass can flake and cause a safety hazard. To be successfully utilized as an aggregate, glass aggregate must receive specialized treatment so that the asphalt will adhere.
  • Ash -- There are many different kinds of ash depending on how the original fuel is burned. The burning process ultimately results in products that have very different properties and applications.  The FDOT primarily uses coal combustion fly ash in concrete where it is used as a replacement for Portland cement. This fly ash is a manufactured product that comes from specific sources and is controlled for its properties. Fly ash in concrete is critical to Florida's transportation system because it helps to reduce the potential for corrosion in structures and the overall cost of concrete. In addition, the FDOT uses ground blast furnace slag as a replacement for Portland cement. The Department has recently completed research optimizing the use of blends of Portland cement, fly ash and slag.

    Some ash products are not suitable for use in concrete but may still be considered as fill materials for embankments or roadway bases. The FDOT has researched and gathered information on the engineering properties of many of these materials.  Sources vary from power plant ash to municipal incineration ash. To date, there is no conclusive information regarding the long term effects of ground water contamination from the use of these materials when placed broadly over areas such as highways.  As a result, the use of many types of ash for roadway construction is prohibited by the Environmental Protection Agency; however, there are exceptions in some localities. JEA in Jacksonville produced hydrated ash from Circulating Fluidized Bed (CFB) boilers and conducted a Beneficial Use Demonstration project to determine the potential for adverse environmental or health effects associated with the use of the processed CFB ash. This testing ultimately resulted in the Department of Environmental Protection designating the CFB ash as an exempt industrial by-product. The FDOT continues to work in partnership with JEA to optimize the engineering properties of this material for use as a roadway material.

The FDOT currently has a technical specification in place for the use of some recycled plastics (e.g. signposts, delineators).  What other types of uses have been explored?

  • The following is a list of recycled plastic products currently evaluated for FDOT specifications: fence posts, delineator posts, guardrail offset blocks, fiberglass fiber reinforced composite lumber, structurally reinforced composite piles and plastic chairs/bolsters. In addition, many other products, such as traffic drums, impact attenuators, object markers and raised pavement markers include recycled content. Ultimately, most materials manufactured from plastic that are used in highway applications have some recycled content.

What consideration has been given to the use of glass as a substitute for aggregate? Potential? Are there other uses?

  • See response above. 

What consideration has been given to the use of crushed concrete? What is its source?  Are there any other sources of "non" crushed concrete that is currently not being used?

  • The FDOT is currently using 100% of crushed concrete. This means that all of the crushed concrete that is produced in the state is currently being utilized and is not available for FDOT work. 

    The FDOT has researched the engineering properties of recycled concrete for use as an aggregate for asphalt, concrete, base material and drainage stone. Crushed concrete varies, however, depending on where it originates and how it is processed.  The current FDOT specifications allow for crushed concrete from an existing concrete pavement to be recycled into a new pavement as base or aggregate material. Specifications also allow for the use of crushed concrete from general construction and demolition waste if the source was previously approved by the FDOT (the source shall have a DEP permit (per section 62-701.730) or be qualified as a clean debris source under DEP's rules to assure that there are no toxic contaminants in the material such as asbestos or lead). 

    Crushed concrete sources that are approved for use by the FDOT include:
    • Kimmins Construction, Tampa, FDOT Mine 10-679
    • Woodruff and Sons, Bradenton, FDOT Mine 13-700
    • Some "non-crushed" concrete (ex. broken slabs) may be used as ditch-lining protection for slope erosion.