In the world of road builders and asphalt haulers, the subject of release agents is sometimes considered one part snake oil and two parts science. Mixture rates vary from release agent to release agent, with no clear guidelines for various asphalt mixtures. State DOT approvals differ from state to state. Wheeled compactors favor one type of chemistry, paving rollers require another, while dump truckers would just as soon use diesel fuel. With state fines for improper use ranging as high as $10,000 and lost production costs soaring, the stakes are high and the information seems cloudy at best.
For years, diesel fuel was the release agent of choice. A pint or two sprayed directly onto the truck bed or tailgate prior to loading was all one needed. The cost was not prohibitive and best of all — it worked. The entire load came out as slick as a whistle with no residue left to form hard spots. Unfortunately, those days are gone forever. Environmental issues and state regulations prohibit the use of diesel fuel as a release agent and the fines are substantial.
New technologies vs. old technologies
Newer formulations challenge the notion that you can't have your cake and eat it too. Cost efficiency and operational effectiveness are being combined in new formulations.
Larry Ludwig, chief chemist for St. Louis-based Schaeffer Mfg. Company, is a leader in developing "hybrid" products that borrow the best characteristics from proven technologies to create formulas that outperform traditional products in polymer and conventional mixes.
"Products can be stable and still be miscible, if you design it that way from the beginning," Ludwig says. "Most companies engineer their products for a particular mix or for a certain piece of equipment. The key is to design the formula around the environment it will be used in."
Ludwig's theory seems to be working. Schaeffer recently received approval of a soy-based product in Illinois, one of the toughest states in which to gain Department of Transportation certification. Illinois requires that the release agent pass all evaluations without being mixed with water. Since most agents are designed to be diluted 20:1 or 30:1, they usually soften the asphalt when evaluated in their undiluted strength. Those that do pass are most often detergent/soap-based products whose effectiveness on tacky, polymer mixes is limited.
Truck beds and compacting equipment
The two primary applications for asphalt release agents are dump truck beds and asphalt compacting machinery. In both types of equipment, the goal is the same: keep the hot asphalt from sticking to the cooler surfaces.
With compactors, when sticking occurs, new asphalt is pulled away from the road surface. Pits form in the layers leading to uneven spreading. Often, expensive and time-consuming removal of the asphalt layer is the only acceptable remedy. Modern release agents are designed to spray continuously onto wheels and drums without clogging nozzles or plugging lines. The best products stay soluble overnight and work well on a variety of asphalt types. With proper adjustment, only a trickle of release agent is needed to perform well in all types of wheeled and drum compactors.
Truck beds need to release the entire load of asphalt so that hard spots don't form in the bed. If they do, the next load could pull a large chunk of cold asphalt into the hot mix making it impossible to get a smooth, even surface. Additionally, truckers often haul other materials that may be discolored or contaminated by residual asphalt from the day's hauls. Many truckers have spent hours cleaning and knocking asphalt out of a bed or off of a tailgate to make sure they can haul white rock the next day. A few have even experienced the pain of a rejected load when an inspector notices clods of asphalt among tons of white stone. Effective release agents not only ensure that the current load is released properly, but can also clean up asphalt deposits that have accumulated from prior loads. This is especially important around the tailgate and nose of the bed.