Pavements

ARCHIVED: Chapter 4. Economics Of Recycling

Introduction

Although started as a method of reusing waste materials, recycling of asphalt pavement has proved to be a cost effective method of pavement rehabilitation. When properly selected, all the different types of recycling methods are usually cheaper than the conventional rehabilitation methods, even though the relative savings will depend on the kind of recycling technique used. The primary saving in hot and cold mix recycling comes from savings in the cost of virgin asphalt cement, whereas the savings in hot in-place recycling comes by elimination of transportation cost and use of very little amount of virgin material. The major savings in the case of cold in-place recycling comes by eliminating the need for fuel or emission control system, since the process is done at ambient temperature, elimination of transportation costs, and the addition of only a small percentage of virgin asphalt binder. The objective of this session is to present the economics associated with the use of recycled asphalt materials. Expenditures and cost comparisons with the use of conventional HMA mixes are summarized from available literature.

Estimated price associated with pavement construction, reconstruction and recycling operations are presented in this chapter. These prices have been collected from available literature. Whenever possible, prices collected from literature published in or after 1990 are generally reported. It should be noted that recycling costs have changed over the years because of continual developments in the recycling technology and equipment. If costs for these operations are available from state or local agency records or from local contractors, they should be used instead since a large price variation can be expected depending on the location of the project and the time of construction.

As presented here, the pavement cost is defined as the amount of monies that a contractor must spend for labor, materials, equipment, subcontractors, and overhead to construct, rehabilitate or maintain a pavement structure.⁽¹⁾

Cost And Savings Associated With Hot Mix Recycling

The cost associated with recycling can be presented on a material cost as well as construction cost basis. Although construction cost may be a more valid approach, an example of material cost comparison is also presented here. This example shows the amount of savings that can be made by using recycled asphalt pavement (RAP) instead of using virgin material.⁽²⁾ Considering $5 per ton and $120 per ton as average costs of aggregate and liquid asphalt, respectively, the cost of a 100 percent virgin mix with 6 percent asphalt comes out to be $11.90 (see table 4-1). If the contractor uses a half-lane milling machine and hauls the RAP back to the HMA plant, his/her total cost for RAP is $3.70 per ton, considering $1.70 per ton for machine and labor for milling, and $2.00 per ton for trucking cost. Hence the savings, compared to using virgin material, is $8.20 per ton, as shown in table 4-1. Table 4-2 shows the savings in using different percentages of RAP. It should be noted that these savings are in first cost. Limiting life cycle costs, if any, must be considered when using excessive amounts of RAP in recycled mixes. Typical cost savings with hot mix recycling are shown in tables 4-3 and 4-4.

Hot In-Place Recycling

There are three primary types of hot in-place recycling, as recognized by the Asphalt Recycling and Reclaiming Association (ARRA). These are: surface recycling, repaving, and remixing.

Surface recycling to a depth of 25 mm (1 in) and addition of a recycling agent costs approximately $1.25/m² ($1.00/yd²).⁽³⁾ A cost of approximately $2.05/m² ($1.64/yd²) is required for an additional 25-mm (1-in) overlay. Hence the total cost of recycling and overlaying by two-pass method will be approximately $3.3/m² ($2.64/yd²).⁽³⁾ In the repaving method, placement of a 25-mm (1-in) overlay along with recycling of the top 25 mm (1 in) of an existing pavement will cost approximately $3.62/m² ($2.90/yd²).^(4,5) A maximum of 25 percent cost savings over cold milling and conventional overlaying procedure has been reported.⁽⁶⁾ The cost of cutting 25 mm (1 in) and remixing with 10 to 20 percent of virgin aggregate is approximately $2.24/m² ($1.79/yd²).⁽⁶⁾ Typical remixing price in Canada is reported to be between $2.78 and $3.70/m² for a 50-mm treatment depth (between $2.22 and $2.96/yd² for a 2-in treatment depth).⁽⁷⁾

In a 101,156 m² (121,000 yd²) repaving job in Florida, it was found that the recycling process used 2.6 trillion joules (2.5 billion BTU) less energy than that required by a conventional method. This was found equivalent to an energy savings of 32 percent.⁽⁸⁾

Table 4-5⁽⁶⁾ presents a recent summary of cost and savings data and case histories. The estimated savings over conventional construction methods ranges from 17 to 50 percent.⁽⁶⁾

Note:

• * Cost for jobs in Canada given in Canadian dollars.

Cold In-Place Recycling

The reported costs of cold in-place recycling are shown in Table 4-6.⁽⁸⁾ The representative cost varies from approximately $1.71/m² ($1.37/yd²) to $9.87/m² ($7.90/yd²) depending upon many factors such as depth of recycling, equipment type, and thickness of overlay. The reported relative savings of using cold in-place recycling in lieu of conventional construction methods are also shown in table 4-6. The initial savings have varied from 6 to 67 percent.

Notes:

1. Relative to commonly used rehabilitation alternatives used by identified states.
2. Personal communication with D. Hanson (1987).
3. Cost increase on one project.

The mean cost from Oregon DOT cold in-place recycling projects in the 1989-1990 period was reported to be $2.51/m² ($2.0/yd²) for a 50-mm (2-in) cold in-place recycling with a chip seal, and about $1.80/m² ($1.44/yd²) without a chip seal.⁽⁹⁾

The mean cost for 48 New Mexico cold-in-place recycling projects ranged from $0.13 to $0.44/m-cm² ($0.27 to $0.92/yd-in²), with a mean of $0.26/m-cm² ($0.54/yd-in²).⁽⁹⁾ Recycling cost increases with an increase in the use of virgin aggregates.

On a per square meter per cm basis cost of recycling is reduced with an increase in depth of cold in-place recycling. For the New Mexico state projects, the mean cost per square meter per centimeter have been reported to be $0.31 for 75 mm ($0.64/yd-in² for 3 in), $0.27 for 85 mm ($0.56/yd²-in for 3.4 in), $0.25 for 10 cm ($0.52/yd²-in for 4 in), and $0.21 for 11.3 cm ($0.44/yd²-in for 4.5 in) of cold in-place recycling.⁽⁹⁾

A recent study shows that the CIR savings in New Mexico amount to approximately $1.90/m² ($1.52/yd²) in initial cost and $2.05/m² ($1.64/yd²) on the basis of life cycle costs. Figure 4-1 shows typical sections resulting from conventional rehabilitation and recycling operations. Cost figures based on initial cost and life cycle cost are also indicated in the figure. The savings on a life cycle basis results from reduced frequency of maintenance for CIR pavements. Generally, maintenance for cracking is required after every four years for mill and overlay projects, whereas maintenance for cracking is required after eight years for CIR projects.

Figure 4-1. Typical sections for conventional and recycled pavement.

Full Depth Reclamation

Cost comparisons of conventional rehabilitation technique and recycling with full depth reclamation and HMA wearing course are given in table 4-7.⁽¹⁰⁾ In this case, the cost of recycling ($7.25/m², $5.80/yd²) is less than one half of the conventional reconstruction technique ($16.12/m², $12.90/yd²).

General Benefits Of Recycling

Apart from savings in materials, recycling saves money by avoiding transportation cost and cost of filling up landfill space. Recycling reuses non-renewable resources. Hence it should be considered even if the cost of recycling is equal to the cost of conventional rehabilitation. Also, in some cases where overlays are restricted to maintaining underpasses, or avoiding raising guard rails, recycling is a better option compared to conventional rehabilitation methods.

Summary

A review of current literature shows that savings up to 40, 50, 55 and 67 percent can be achieved by using hot mix, hot in-place, cold in-place recycling, and full depth reclamation, respectively. These savings are achieved when one of the recycling methods is used in place of conventional method or some other recycling method. In addition to the material and construction cost savings, significant amount of cost savings (in terms of user costs) can be realized by the reduced interruptions in traffic flow when compared with conventional rehabilitation techniques. Recycling can be used to rejuvenate a pavement or correct mix deficiency and conserve material and energy - options not available with the conventional paving techniques. A conventional overlay may require upgrading shoulders to maintain profile, raising guard rails to maintain the minimum safety standard, and restrict overlays below the bridges to maintain underpass height. On the other hand, recycling can effectively be used to maintain the highway geometry and thus resulting in substantial overall savings as well.

References

1. Pavement Recycling Guidelines for Local Governments - Reference Manual, Report No. FHWA-TS-87-230, FHWA, U.S. Department of Transportation, Washington, DC, 1987.
2. J. D. Brock. Milling and Recycling, Technical Paper T-127, ASTEC, Chattanooga, TN. Undated.
3. J.E. Shoenberger and T.W. Voller. Hot In-Place Recycling of Asphalt Pavements, Technical Report GL-90-22. Department of the Army Waterways Experiment Station, Corps of Engineers, Vicksburg, MS, 1990.
4. J.R. Rathburn. "One-Step Repaving Speeds Country Work," Roads and Bridges, March, 1990.
5. G.M. Perry. "Repaving...One More Time," Southwest Contractor, June, 1990.
6. J. Button, D.N. Little, and C.K. Estakhri. Hot In-Place Recycling of Asphalt Concrete, In NCHRP Synthesis of Highway Practice 193, TRB, National Research Council, Washington, DC, 1994.
7. Personal communication with L. Dunn, Pavement Recycling Technologies Inc. (PR7) Alberta, Canada, 1997.
8. J.A. Epps. Cold Recycled Bituminous Concrete, In NCHRP Synthesis of Highway Practice 160, TRB, National Research Council, Washington, DC, 1990.
9. G.R. Hicks and D.F. Rogge. "States Gain Cold-Cash Saving Using Cold In-Place Recycling," Roads and Bridges, October, 1995.
10. "Pavement Recycling," Maine Local Roads News. January, 1993.