Strategic Highway Research Program Reports on Pothole Repair Survey

The Spring 1993 issue of “Moving Forward,” published by the Pennsylvania Local Roads Program, summarized information from SHRP’s 1991 report, which was called “Innovative Materials and Equipment for Pavement Surface Repairs.”

Pavement Maintenance Costs

SHRP undertook this survey to help public entities control pavement costs. Pavement maintenance activities are a significant portion of highway operation budgets for several reasons: (1) the initial cost of pavement maintenance is high, (2) maintenance repairs generally perform poorly, and (3) safety and liability expenses related to pavement maintenance activities can be very high.

Purpose and Design Of Survey

To find ways to reduce pavement maintenance costs, SHRP’s survey gathered information on the types of pothole repair materials available and how well each had performed under certain conditions.

The types of patching materials studied were:

1. Conventional asphalt hot and cold mixes typically specified by state DOT’s using certain percentages of asphalt cement (hot-mix) or emulsion or cutback asphalts (cold-mix) and strictly graded aggregate.
2. Modified/proprietary asphalt materials which include the addition of modifiers (rubber, fiber, sulfur, antistripping agent) and specially employed production processes. Examples of the more commonly used materials are Sylvax UPM, Perma-Patch, Fiber Pave, Bonifibers, and QPR 2000.
3. Proprietary cement concrete mixes using cementitious materials. Examples are Duracel and Set-45.

Surveys attempted to learn each material’s effectiveness when applied using either temporary or permanent patching procedures at temperatures either above or below freezing (32 degrees Fahrenheit) and under wet or dry hole conditions. For purposes of the survey, a temporary pothole patch was one applied with little or no preparation and compaction. A permanent patch was applied with proper preparation and compaction.

Survey Results

Using permanent procedures to apply conventional hot and cold mixes in dry holes at temperatures above 32 degrees F. produced the longest-lasting patches. Hot-mix lasted up to six times longer when placed in a dry hole versus a wet hole, and cold-mix lasted three times longer when placed in a dry hole. Permanent procedures doubled the life of both hot-mix and cold- mix patches, and placing patches at temperatures above freezing tripled the life of the patch for both hot and cold mixes when compared with placing the patch in below-freezing temperatures.

Proprietary mixes had 1.6 times longer life when placed in a dry hole rather than a wet one, and 1.1 times longer life when applied in above-freezing temperatures.

Survey respondents rarely mentioned proprietary cement mixes. The article commented, “These types of materials are normally not recommended due to thermal and chemical incompatibilities between the asphalt pavement and the patch material.”

For cold-mix patching, Sylvax UPM, PennDOT 485 Cold-Mix, and Minnesota’s Cold-Mix Spec 2381 received good performance reports. Overall, proprietary materials outperformed average conventional cold-mix under cold temperature conditions and in wet holes– lasting about 3.5 times longer. For cold temperatures and in dry holes, the proprietary materials had the best performance– lasting about twice as long as conventional cold mixes. Under warm conditions, proprietary materials did not significantly outperform conventional materials.

Summary

Survey results showed:

[P]ermanent patching procedures improve patch life. Warm temperatures improve patch life. And dry holes significantly improve patch life. Proprietary materials are designed to improve performance under cold and wet conditions.

But the greatest result, supported by the experiences of many agencies and this research study, is the conclusion that: “Bituminous hot-mix has shown the longest service life of all materials when it is placed using permanent procedures in a dry hole.”