An important candidate for the application of recycled materials is traffic sign blanks or substrates, (the structural element on which information is presented). Approximately $250 million is spent each year in maintaining 58 million traffic signs that are spread over 3.8 million miles of roads, streets, and highways in the United States. Increasing the use of recycled materials for sign substrates could mean significant savings in direct replacement costs and reductions in detrimental environmental effects. Research programs are underway in many states that are seeking to find alternative substrates for signs with State and Federal agencies testing these new substrates in the field. The ultimate goal is to reduce material and maintenance costs.
Texas currently uses sign blanks made from either high-grade plywood or aluminum. The costs for these materials are constantly increasing, and the ultimate disposal of these materials is contributing to landfill problems. Finding alternative materials for use as sign blanks that can reduce life-cycle cost and aid the environment is becoming a high priority. In response, industries have developed composite material substrates made of: recycled plastic, fiber-reinforced plastics, rubber-plastic blends and alloys made of recycled aluminum.
In order to use a recycled material as a sign substrate, a method for determining the required thickness of a particular material must be available. However, the thickness dimension of sign blanks made from marine plywood or aluminum in current use along Texas highways is not designed according to engineering formulas. Rather, specifications are based on field experience over many years of installation. Newer materials, such as recycled plastics, have different properties than the traditional substrates and a database of practical experience is not available. Therefore, it is imperative that tests be conducted to characterize the behavior of several of these new materials.
Knowledge of these properties, in turn, enables a design procedure to be developed. In this way, required sign thickness manufactured from virtually any suitable material can be specified, taking into account properties such as density, stiffness, strength, as well as the geometry of the sign and its supports.
The Texas Transportation Institute conducted study 0-1338, "Recycled Content Sign Blanks", to determine the feasibility of using sign blanks constructed of reclaimed materials instead of conventional high-grade plywood and aluminum.
The primary objective of this study was to develop a procedure by which candidate recycled materials may be evaluated, designed for use as sign blanks, and analyzed. The components of the study were to:
For this study, various types of recycled materials were solicited from commercial manufacturers and subjected to an array of laboratory tests and numerical simulations. These recycled materials included high-density polyethylene, polycarbonate, polyvinyl chloride, and calcium carbonate. A total of seven recycled materials were tested for flexure, uni-axial tension, creep, free vibration, and exposure to ultraviolet radiation. Performance and properties of the tested materials are included in the study.
Aluminum and wood are the substrates most frequently used for traffic signs. Grades 6061 (heat treatable) and 5052 (non-heat treatable) aluminum alloys are widely used. Currently, grade 3000 aluminum alloys, which are made primarily from recycled aluminum, are also being specified.
In order to purchase consistent quality recycled sign blanks, it is necessary to develop a procedure by which the blanks may be designed and certified. A need for design procedure results from variability in: densities, mechanical properties, and serviceability of substrates produced by manufacturers of recycled products. As recycling technologies advance and the quality of recycled materials improve, a design procedure for roadside signs will enable a material supplier to closely match the material properties and serviceability of their products with the specific need.
Researchers concluded that recycled sign blanks need to be durable in diverse climatic conditions, and be ductile and able to dissipate energy of vibration at a reasonable rate.
Draft specifications for two-pole supported and tee-pole supported recycled content sign blanks were prepared. These specifications include: general characteristics, mechanical properties, preliminary performance requirements (panel smoothness, adhesion, impact resistance, creep, and workability), and secondary performance requirements (mechanical tests, wind simulation, thermal stability, and field testing).
A rational design procedure based on ASCE 7-95 and various deflection criteria was also developed. This procedure, when incorporated with the proposed performance specifications, provides a method that allows recycled materials to be approved for use as sign blanks. The procedure also makes it possible for the design of sign blanks to become more efficient as more information is gathered on the types of wind and environmental loads to which roadside structures are subjected.
Researchers recommended that additional work be conducted, including:
The contents of this summary are reported in detail in Texas Transportation Institute Report 0-1338, "Recycled Content Sign Blanks," Paul N. Roschke, Ben F. Harrison IV, and Fred Benson, October 1996. This summary does not necessarily reflect the official views of the FHWA, USDOT or TxDOT.