Issues Page 1

The most common objections to using A-R are high initial costs, recyclability, hazardous emissions, and expensive equipment modifications. These issues have been adequately addressed by a large number of research projects and reports and also through long standing construction evaluation. For the sake of brevity, the most notable reports are discussed in this paper.

1. High initial costs
Costs are higher than conventional asphalt per unit ton until economies of scale are in place. An example, Arizona experienced relatively high costs until the patents expired and more contractors competed for the work. Currently, the price differential between conventional and A-R hot mix is about $10.00 per ton. The falling cost trend for liquid asphalt rubber is depicted in Figure 1.

Figure 1 Asphalt Rubber Binder Prices experienced by ADOT (Way, 1999)

Initial costs are actually lower when thickness equivalency ratios are utilized. Less material can be used due to increased durability and strength in asphalt-rubber, at times the ratio is 2:1. An example of an equivalency table is provided by Caltrans in Table 1.

Table 1 California Department of Transportation Design Guide for ARHM Gap Graded.

CALTRANS Structural Equivalency Tables (Thickness in feet)

Notes: The maximum allowable non-experimental equivalency for ARHM-GG is 2: ARHM-GG may not prevent cold weather induced transverse cracks.
D CAG - Dense Grade Asphalt Concrete ARHM - Asphalt Rubber Hot Mix GG- GAp Graded SAMI - Stress Absorbing Membrane Interlayer

a - The minimum allowable
ARHM-GG lift thickness is 0.10'

b - Place 0.15' of new DGAC first

c - Place 0.20' of new DGAC first

2. Lifecycle Economics

Until a study by Hicks, Lundy, and Epps, the economic savings related to A-R were not clear. (Hicks et al, RPA 1999) Evidence of savings had been published in a variety of reports regarding reduced maintenance costs and reduced lifts, but never by using the Life Cycle Cost Analysis model adopted by the FHWA. Now it is evident that savings can be achieved when using A-R in most cases. Table 2 indicates the deterministic savings projected by using various asphalt-rubber paving strategies where appropriate compared to conventional strategies.

Table 2 LCCA (Hicks et al, RPA 1999)


Scenario	Present Worth($/yd)	Savings w/AR
Preservation - Chip Seal
Conventional	18.39
Asphalt Rubber	15.87	2.52
Preservation - Thin HMA
Conventional	20.69
Asphalt Rubber	17.33	3.36
Structural Overlay
Conventional	21.97
Asphalt Rubber	14.63	7.34

Maintenance costs are significantly reduced when pavements resist cracking.
An example of reduced maintenance cost associated with A-R compared
to conventional material is provided by Figure 2.

Figure 2 Maintenance Cost dollars per lane mile ADOT, Conventional overlay and inlay
materials compared to Asphalt Rubber Asphalt Concrete Friction Course (Way, 1999).

Figure 3 depicts reduced cracking on an asphalt rubber overlay in a test section of Interstate 40 near Flagstaff, Arizona, USA. This test section includes a number of overlay strategies which were placed in 1990 for evaluation by the Arizona Department of Transportation. The sections have identical sub grade and base construction. The test overlay using conventional materials was placed in a thickness of four inches (10.16 cm), the test section using rubber was placed at a depth of two inches (5.08 cm). The section is located at about 7000 feet (2133 m) above sea level and experiences nearly 100 inches (2.54 m) of annual snowfall.

Figure 3 US Interstate 40 near Flagstaff, Arizona. 4" conventional asphalt (left) and 2" asphalt rubber overlays on Portland Concrete Cement placed in 1990, photo taken 1998.