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Glass Cullet in Roadway Construction

Successful recycling collection programs have produced large quantities of broken glass, or cullet, in many parts of the country. Glass cullet is primarily reused to manufacture new glass containers.

Using glass cullet in roadway construction would eliminate the need for expensive sorting and offers an opportunity to use glass cullet as aggregate in parts of the state where aggregate sources are scarce.

Study

The Texas Tech University College of Engineering conducted study 0-1331, "Use Of Glass Cullet In Roadway Construction", for TxDOT, the Federal Highway Administration (FHWA),and the Texas Commission on Environmental Quality (TCEQ) to identify sound engineering and environmental uses of glass cullet in roadway construction and maintenance projects and develop specifications for each successful use of glass cullet evaluated based on current TxDOT specifications.

Specifications for using glass cullet in roadway construction were developed through the following three phases of study:

  1. Literature review and identification of available sources and suppliers, including:
    1. A recommendation of which glass cullet uses appear the most feasible and promising
    2. Potential disadvantages or obstacles to these uses
    3. Potential effects on future recyclability
    4. Limited economic analysis comparing the use of glass cullet with currently utilized materials for the selected applications
    5. A description of available sources and suppliers in Texas.
  2. Laboratory testing. Laboratory testing was conducted to provide information not available from the literature search or to assure the accuracy of information found. Testing focused on problem areas identified by other researchers.
  3. Specification development. Specifications were developed for each successful use of glass cullet evaluated in the course of this study, following TxDOT current specification formats and requirements.

The economic viability of glass recycling for highway construction depends upon the market situation in a given area. Highway professionals with experience using glass cullet and industry experts in the glass recycling industry indicated that if there were a market for glass cullet in the highway industry, it would be economically competitive with other materials in major metropolitan areas and their surrounding vicinities. These professionals also indicated that a market for color-mixed waste glass could significantly increase glass-collection efforts in recycling programs.

In general, using glass cullet in asphalt concrete is not considered as attractive an option as other uses due to problems associated with asphalt stripping in moist conditions. The use of glass cullet in portland cement concrete is not feasible due to the high levels of alkali-silica reactivity associated with it. This problem is considered to be particularly acute with fine cullet.

This study and others have concluded that:

  1. From an engineering standpoint, cullet appears to be an excellent supplement or replacement for gravel in many construction applications.
  2. There has been no appreciable environmental impact when cullet has been tested for harmful contaminants and potential for leaching over time.
  3. Since glass contains silica rather than crystalline silica, it does not have the health risks associated with natural sand.
  4. In many cases, and depending on local conditions, using glass can be cost-competitive or less expensive than using conventional aggregates.

Based on available information, from an engineering standpoint glass cullet is suitable for a variety of uses. The economic feasibility varies depending on the locale and availability of glass in large quantities. Specifications were developed for the following applications:

TxDOT Item # Application Percentage of Glass Cullet Permitted
132 Embankments Shall not exceed 20 percent by weight of the total mix
247 Flexible base (Type D) Shall not exceed 20 percent by weight of the total mix
301 Asphalt anti-stripping agents When cullet is used as an aggregate in asphalt-stabilized bases, lime and some liquid anti-stripping agents may not perform adequately
345 Asphalt-stabilized base Shall not exceed 5 percent of the total weight of the aggregate
400 Excavation and backfill for structures
  • Utility bedding material may comprise up to 100 percent.
  • Backfill that will support any portion of roadbed or embankment shall include less than 20 percent.
  • Backfill that does not support any portion of the roadbed or embankment may include up to 100 percent.
423 Retaining wall Structural backfill limited to maximum of 20 percent. Non-structural backfill up to 100 percent.
556 Pipe under drains Up to 100 percent.
Other Open-graded base courses The use of cullet in this application shall be governed by Item 345, "Asphalt-stabilized base." Not to exceed 5 percent.

The contents of this summary are reported in detail in Texas Tech University College of Engineering Research Reports 0-1331-1 and 0-1331-3, "Use Of Glass Cullet In Roadway Construction," Phillip T. Nash, Priyantha Jayawickrama, Richard W. Tock, Sanjaya Senadheera, Krishnan Viswanathan, and Binli Woolverton, August 1995. This summary does not necessarily reflect the official views of the FHWA, TCEQ, or TxDOT.