All Pavements Are Created to Perform Equally, or Are They?

It's no secret that going "green" is gaining momentum within the asphalt industry just as it is within other industries around the country. Increasing reclaimed asphalt pavement (RAP), incorporating a percentage of shingle content (new rejects or old tear-offs), adding crumb rubber (recycled tires), and producing warm mix lowers the cost of maintaining quality road systems and reduces the consumption of valuable resources, including aggregates and petroleum.

Being green is good for road agencies and taxpayers who want to keep costs down and for government agencies that want to do their part as environment stewards. The above new mix designs presumably deliver the same quality performance as virgin hot mix, but the question is at what expense. Do the asphalt plants, for example, have to reconfigure their operations and technology to accommodate "sustainable" asphalt and are test equipment manufacturers confident that current technology can ensure that all pavements are created to perform equally.

RAP not an issue

From both the plant and testing perspectives, reclaimed asphalt pavement poses few if any challenges. Used at least once already, RAP should have all the right ingredients to make another quality road. The same cannot be said for shingles, especially the tear-off variety, say automation manufacturers.

Systems Equipment Corp. and WEM Automation both provide the computer technology -- the controls, software, and systems -- to automate plants. "The challenge with singles, especially tear-offs, is that one must continually know the amount being added," says Systems Equipment's Dave Enyart, Sr. "As a rule, shingles have high oil content. If the plant cannot get a handle on this material flow, it cannot regulate the asphalt content of the mix.

Enyart gives this example. "Let's assume you're making 100 TPH of mix with a desired mix AC content of 5 percent, using 80 TPH of virgin material and 20 TPH of recycle material with 5 percent oil content. If we replaced 5 percent of the recycle material with shingles, having an oil content of 20 percent, any change in the shingles rate makes a big AC content swing in the end product.

"Our job is to provide automation and plant hardware to assist in accurately monitoring any changes in the shingles rate. Integrating this information in a timely fashion allows for a consistent final product."

As he points out, the automaton and systems can handle the variety of recycled material if there are few surprises. James Phillips, vice president of construction for WEM Automation agrees. "The automation can handle the variety. It can program the plant equipment to run RAP with a 5 percent oil content and shingles at 40 percent. What it cannot make up for is inconsistency."

The other challenge, he adds, is within the plant itself. "As automation specialists, we have to work more closely with plants to ensure they have the right feed systems and other equipment in place to run the recycled material. A plugged or slowed feeder line running recycled material, for example, can mess up a mix in a hurry. To avoid this, plants need to have the best equipment in the best shape possible."

Phillips and Enyart are convinced that the recycle trend is not a fad because it saves on costs, energy consumption and valuable resources. Whereas tear-offs present some difficult challenges from a production point of view, the recycle movement as a whole has been and will continue to be well received. Phillips is equally enthusiastic about the prospects warm mix brings to the table.

"Warm mix is becoming more popular and is here to stay," he emphasizes. "Plants use approximately one-third less energy to produce warm mix versus hot mix and it has proven to be very workable at the job site."

If there is a challenge, though, it's on the testing side, according to one gauge manufacturer.

Not ready for prime time