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TRANSPORTATION RESEARCH DIGEST

ARIZONA TRANSPORTATION INSTITUTE

e-mail jsemmens@cox.net

NOVEMBER 2005

Thin Maintenance Surface Treatments Comparative Study in Transportation Research Record 1866 by Charles T. Jahren and Kevin R. Behling, (Transportation Research Board, 2101 Constitution Avenue, N.W., Washington, D.C. 20418; ph. 202-334-2934; http://www.national-academies.org/trb/bookstore) (2004).

Highlights

Thin maintenance surfaces (TMSs) provide an economical method of extending the life of an asphaltic concrete or bituminous pavement.

The condition of many of the test sections indicated that when TMSs are properly selected and applied, they can improve the PCI and SR of a pavement. Several requirements must be met for success, including proper material selection, design, application rate, workmanship, and material compatibility as well as favorable weather during application and curing. A deficiency in anyone of these factors may degrade the pavement condition index (PCI) or skid resistance (SR).

The thin hot -mix treatments that were applied as part of this project performed well. Although the initial costs of overlays were higher than those of thin surface treatments, these costs could be recovered if the benefits of these treatments outlasted the benefits of TMSs by a sufficient amount of time.

When TMSs are used on roads subjected to high traffic volume, in relatively good pavement condition, or both, more effort is necessary in the areas of TMS selection, materials selection, and construction quality. On a high-volume road, more road users are exposed to problems during and after construction by default, and the downside of a poor result is greater because more users will be exposed to the problem. For roads in good pavement condition, even a small problem with

the TMS can degrade the pavement condition as a result of the TMS application.

The designed chip seals were more effective than ones constructed according to standard application rates. Test sections with chip seals designed using the Minnesota DOT's method performed well (with some exceptions, especially the quartzite chip seal) and used two-thirds to three-fourths of the amount of material normally used under 2002 Iowa specifications. Because the cost of chip seal construction depends highly on materials, it is expected that most of the savings will be passed on to the road jurisdiction.

Some problems with bleeding were noted, but this defect can be mitigated with proper design and application. A polymer-modified binder probably would be helpful in controlling bleeding because it is stiff at high temperatures and unlikely to flow.

Graded cover aggregates for chip seals have performed well, producing tight, quiet surfaces. These tight surfaces also seem to be beneficial to reduce snowplow damage. The literature typically states that one-size aggregate bonds best to a road surface because it has more void space for binder. Another explanation in the literature claims that direct adhesion to the treated pavement is achieved because it is easier to spread materials that are one stone thick. More room exists for error in binder application rates, because the extra void space provides additional capacity for excess binder. However, this research indicates that application rates can be controlled sufficiently

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