Use of Glass Cullet in Roadway Construction

Problem Statement

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 cullet in glassmaking saves energy and reduces costs. But using cullet also has limitations, primarily due to the need to avoid color contamination and to the cost of transportation. Supplying cullet to furnace-ready specifications requires expensive color sorting, and because of its relative high density, glass cullet is expensive to transport long distances.

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.

Objectives

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.

Procedures

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.

Findings

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.

Other DOTs' specifications indicate there are a variety of uses for glass cullet, ranging from asphalt concrete to drainage backfill.

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.

Implementation

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:

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.