Moisture Measurement Gets the Right Mix
BY Del Williams
In the asphalt pavement industry, accurate moisture measurement is vital to producing and laying a durable, quality surface at all stages of the process. During the production, hauling and paving process, the moisture content of hot-mix asphalt (HMA) can vary due to environmental conditions or water vapor loss as the mix is heated, stored and dispensed at temperatures up to 350° Fahrenheit. This variability can affect the quality, thus longevity of the finished asphalt.
To ensure the moisture content remains consistent, operators would ideally test it at every step of the way. Unfortunately, many moisture meters require calibration, sampling and time. Many of the tools are not portable or durable enough to be used on heavy construction job sites.
Now with the availability of cost-effective, automated and instant moisture measurement devices, the industry is turning to these options to ensure optimal moisture levels from the plant to the paving site to improve their outcomes.
“Asphalt producers are beginning to understand that the cliché ‘you can’t expect what you don’t inspect’ applies to moisture measurement,” said John Bogart, managing director of Kett US, a manufacturer of moisture and organic composition analyzers. “And with new, more accurate, easy-to-use, real-time moisture measurement devices, they can improve asphalt quality and longevity by adjusting the mixture at any step from the plant to the ground.”
“As recycled materials become a larger percentage of the inputs for asphalt production, composition analyzers will also play a role.”—John Bogart
Ensuring Critical Moisture Levels
According to Bogart, one traditional approach to test for moisture content involves Loss on Drying testing. This uses a moisture balance to measure the total change in the material weight change of a mixture after drying. However, such tests typically require technicians to prepare a sample to be brought to a lab. Each test takes upward of 15 minutes to several hours to perform.
“Another challenge with moisture balances is that there is a limit to the weight of the sample you can place in one, which can be an issue with asphalt. Larger samples require a big drying oven, a big pan, and often overnight drying,” Bogart said.
To ensure consistent moisture content at HMA plants, the industry now uses Near-Infrared (NIR) light equipment for a highly accurate, non-contact, secondary-measurement method that delivers immediate, laboratory-quality moisture readings.
“NIR moisture meters allow very accurate instant measurement of solids, slurries and liquids without contact or sample preparation and come in desktop, handheld portable and inline models,” Bogart said. “When integrated with data collection and analysis software, inconsistencies can be quickly detected and corrected.”
For real-time testing of HMA, either during plant processing or dispensed to and from trucks, inline tools can be used for 100% inspection of all mixed materials without having to take samples offline for testing. Moisture analyzers such as Kett’s KB30 are designed to provide an instant, non-contact, non-destructive measurement of liquids and solids while the product is moving. The unit’s small form factor allows for simple placement when updating or retrofitting existing process lines.
For frequent spot checks of various materials anywhere in the process, operators can use portable, handheld and instant moisture meters like the KJT130. The design of the unit allows it to be used wherever necessary on both stationary and moving materials, including those on a process line. The user simply points the instrument at the material and the moisture content is instantly shown on a digital display, with results accurate to 0.01% in a 0-100% measurement range, according to the manufacturer.
Desktop NIR moisture analyzers, like the KB230, display results immediately, and are designed for job sites that need continuous sample measurements.
Once technicians lay the asphalt, Kett’s handheld HI520-02 measures not only the road surface but also sublayer moisture to ensure proper curing.
For asphalt producers or contractors that also want to analyze the composition of the mix, NIR composition analyzers are available. Kett’s KJT700 is designed to verify the correct quantity of additives and binders, as well as recycled materials in the mix such as tire rubber, reclaimed asphalt pavement (RAP), asphalt shingles (RAS), slags, glass and so on.
“As recycled materials become a larger percentage of the inputs for asphalt production, composition analyzers will also play a role,” Bogart said.
For those in the industry who may be less familiar with moisture measurement, or previously considered it impractical, Bogart points out that recent advancements now make it quite affordable.
“It is a misconception that moisture measurement [of asphalt and pavement products] is difficult or costly today,” Bogart said. “Automated inline moisture measurement for the plant or haul truck, for example, costs as little as $10 per business day on lease for 100% inspection of all materials and can free an operator from spot checking to perform other higher-value tasks. Compare that to paying an hourly rate to an employee to do occasional spot checks of small amounts of material.”
As the asphalt industry strives to improve the bottom line, a growing number of professionals will utilize automated, instant moisture testing and composition analysis to promote superior quality and performance, which ultimately translate into greater profitability.
Del Williams is a technical writer based in Torrance, California. For more information, call (800) 438-5388 or visit www.kett.com.