To the editor: Several members of our organization had an opportunity to read your article in the April 23 edition entitled "New 'thin-mix' tried as an alternative to tar and chip rehab. " We thought it was important to draw your attention to a few items.

The article spends a good deal of time discussing tar-and-chip surface treatments. It should be noted that tar-and-chip is an out-of-date vernacular term for this style of surface treatment. Because of the harmful volatile organic compounds (VOCs) found in tar, the petroleum base product used for this surface treatment is a water-based emulsion. The process is more appropriately referred to as seal coat or chip seal.

It is also important to note that there appears to be some confusion as to the type of process used and the correct nomenclature for the product. The article refers to "tar-and-chip" (chip seal) and microsurfacing as one in the same type of treatment. They are, in fact, two very different types of surface treatments that use different emulsions, aggregates and design criteria. Chip seals involve the application of a prescribed amount of asphalt emulsion (not tar) sprayed by a calibrated distributor truck followed by a prescribed amount of aggregate placed on top of the emulsion by a chip spreader. The new wearing course is then rolled with a rubber tire roller. In many cases, the surface is ready to support traffic within 15-20 minutes of treatment - minimizing the amount of traffic delay and inconvenience to the motoring public. This process is generally limited to roadways with 5,000 average daily traffic or less, although the process has been placed on high traffic roads with great success in other parts of the country.

Microsurfacing is a polymer modified emulsion and aggregate mix that is applied directly from the back of a specialized truck onto the road. The surface treatment is a mixture of asphalt emulsion, aggregate and cement filler applied to the road by the specialized truck. Microsurfacing requires a thorough mix design be completed prior to construction, which further enhances the quality control and quality assurance aspect of the process.

Because the process is mixed in-place on the road you experience none of the stone loss or " whip off" that is sometimes experienced on a chip seal-treated road. The road can be turned back to traffic within an hour of application, again greatly minimizing the impact to the motoring public. This process has been used with great success by every district in PennDOT, District 3 included. In general, there are no traffic restrictions to this process. In fact, several high volume feeder roads and many arterial roads such as Interstate 80, 180 and sections of the Pennsylvania Turnpike have recently been treated with microsurfacing.

As the trade organization in Pennsylvania representing asphalt pavement maintenance and lower cost asphalt rehabilitation methods for roads, our focus is to ensure that PennDOT, local townships and the motoring public in Pennsylvania are as informed as possible of all the relevant facts on those processes.

We openly recognize the need for a wide variety of treatments, rehabilitation methods and reconstruction in order to maintain the vast road network within Pennsylvania's borders. Chip seals, microsurfacing and the experimental thin lift hot mix asphalt are all important tools in the tool belt available to PennDOT and the local townships as they work to maintain the network we all depend on.

Additionally, we continue to push the boundaries of innovation in attempt to find more effective, longer lasting and cost-effective surface treatments for the agencies responsible for road maintenance. Soon, we expect to see several exciting commercial rollouts of new and improved processes that will greatly enhance the "tools in the PennDOT tool belt" and bring overall greater value to the taxpayers.

Steve Fulk

Executive director

Pennsylvania Association of Asphalt Material Applicators