Use of Waste Toner in Asphaltic Concrete

Problem Statement

Every year, a tremendous amount of toner is produced for copiers and printers by toner manufacturing companies throughout the United States. Some of this toner does not meet quality specifications and consequently becomes a waste product of the manufacturing process. This manufacturing waste, along with spent toner (residue) from copiers and printer cartridges, is dumped into landfills for lack of a better way of utilizing the material.

Objectives

The objective of this study was to identify a use for waste toner, as an asphalt binder modifier, as an alternative to sending the material to landfills.

Findings

A cooperative research project undertaken by the Texas Department of Transportation and the University of Texas at Austin investigated the feasibility and potential benefits of utilizing waste toner in hot-mix asphalt concrete. The research program included procuring a number of different spent toners, blending them with asphalt cement at different ratios, and evaluating the binder and mixture properties resulting from the waste toner addition. Superpave binder performance tests – including complex shear modulus at high and intermediate temperatures, low-temperature creep stiffness, and rotational viscosity – were used to evaluate binder properties. In addition, a Superpave mix design was carried out for three different levels of toner modification (0 percent, 5 percent, and 16 percent, by mass of asphalt binder-toner blend). The modified binders were used in asphalt-aggregate mixtures to evaluate mixture behavior and properties. Hveem stability, resilient modulus, and indirect tensile strength were measured and evaluated.

The results of this study indicated that as the amount of waste toner in the blend increases, the stiffness and viscosity of the binder increases. The increase in stiffness is evident at high, intermediate, and at low temperatures. The mixture analysis also indicates higher strength and stability for toner-modified asphalt concrete, compared with unmodified mixtures. The increase in binder stiffness at high temperature is a positive effect, since resistance to permanent deformation is increased. However, increase in stiffness at low temperatures is not favorable because of the increased potential for low-temperature cracking. However, the toner-modified binder is expected to perform satisfactorily in areas where permanent deformation is of great concern, and where some increase in low-temperature stiffness will not cause cracking problems. Researchers found that an AC-20 asphalt cement (based on the viscosity grading system), which is graded as PG64-28 in the Superpave performance grading system, will grade as PG70-22 with the addition of 10 percent waste toner. In north and central Texas, a PG64-22 asphalt cement is expected to perform satisfactorily, based on a 98 percent reliability. Therefore, the AC-20 asphalt cement modified with 10 percent waste toner, as investigated in this research, satisfies the performance criteria for such regions.

Implementation

There are two general approaches for incorporating a material such as waste toner into asphalt mixtures. One is by directly adding dry toner to the aggregate; the other is by incorporating the toner into the asphalt cement. This latter approach can be performed either through direct incorporation of the dry toner into the asphalt or through a medium such as oil, a dispersing agent, or water in conjunction with an emulsifying agent. Because dry toner was directly introduced into the asphalt binder with success in this research program, this approach is recommended.

The contents of this summary are reported in detail in the Center for Transportation Research’s report #3933-1F, “Use of Waste Toner in Asphaltic Concrete” by Mansour Solaimanian, Thomas W. Kennedy, and Robert B. McGennis, dated February 1997. This summary does not necessarily reflect the official views or policies of the Federal Highway Administration or the Texas Department of Transportation.

TxDOT Patent for Toner-modified Asphalt Compositions

TxDOT received a patent for toner-modified asphalt compositions on September 5, 2000, that addresses the need for a satisfactory disposal method for waste toner, as well as the desirability of improving the properties of asphalt cement with lower cost modifiers. The patent includes preferred methods for making the modified asphalt cement by blending toner with asphalt cement, methods of using the modified asphalt to make hot mix asphalt concrete, and methods of paving a driving surface with the modified hot mix.