Binder extraction, a never-ending challenge
Binder extraction is probably the most common test in an asphalt laboratory. Whether you work for one of the top research laboratories in your country, or your laboratory is housed in a container in the middle of nowhere, your knowledge on the mix properties starts from the verification of the recipe: basically, binder content and aggregate gradation.
A dangerous solution
For a long time, solvent extraction has been the only solution.
Chlorinated solvents, such as TCE, were readily available as also used by other industries, for example dry cleaners. In addition, dangerous fuels, such as gasoline, were used in some countries. As their popularity grew, users also became increasingly aware of their associated dangers over time. Most of the solvents were progressively found to be either toxic or carcinogenic, so their use became limited and, in some cases, even banned. Their use in laboratories was only permitted under special safety regulations, but associated costs increased exponentially.
Gone with the wind
The first solution to the solvent management problem seemed to stem from ignition furnaces. The idea of burning binder instead of melting it with a solvent found a lot of supporters. Ignition ovens reduce safety risks and minimize environmental issues to just smoke emissions. Now they’ve even been further improved by the use of filters or after-burner systems. The extraction by ignition is fast and totally automatic. And it almost doesn’t require any maintenance.
The perfect solution? Unfortunately, not yet.
Some testing procedures require to collect a binder sample after extraction, for further analysis. Unfortunately, with ignition extraction, all the binder is lost into the fumes. In addition, extraction precision is not as good as with the solvent method as the ignition process is burning more than just the binder. A very small moisture content, or a small percentage of the fines, are lost with the solvent. This creates errors.
All test standards require for every mix to calculate and apply a correction factor, by verification of a laboratory mixed sample or by comparison with solvent extraction. This operation may be time-consuming based on the daily number of mixes to be tested.
Fully sealed – The downsides of ignition furnaces still created a need for solvent extraction. And finally, a new technology came to the rescue. Fully closed solvent extraction systems are now able to solve the two main problems related to the use of solvent.
First, the contact between the solvent and the laboratory environment is eliminated, solving both safety and environmental issues.
Second, you no longer need to use clean solvent normally associated with this method. New systems are all-in-one units that comprise an extraction chamber, a high-speed centrifuge for filler separation, a solvent recycler and aggregate dryer unit, and can perform the whole procedure in fully automatic way. The unit combines quality and repeatability of the extraction results with optimal environmental performances. Thanks to the fully sealed technology, solvent emissions in the laboratory are practically zero, and well within OSHA exposure limits. And the solvent is recycled at 99% after the extraction, ready to be used for additional tests. The integrated dryer allows you to collect aggregates that are 100% free from solvent, reducing the solvent contamination in the laboratory.
There’s still a long way ahead of solvent extraction. The future involves new challenges, such as alternative solvents or different materials added to the mix, but fully closed solvent extraction systems will be part of it.
If you would like to find out more about solvent extraction, take the time to read the IPC Global's insightful white paper stating the case for automated asphalt extraction. This safe solvent-based extraction method of asphalt binder from asphalt mixtures makes extractions safer, faster and easier.