This material is exhibiting a softer response. However, where material produced at a lower temperature encounters less aging, the tests results generally show that warm mixes aren’t performing as well as the hot mix in a laboratory test setting.
“Most, if not all, warm mixes we’ve evaluated on the mobile laboratory show laboratory performance test results that indicate the WMA does not provide equivalent test results to hot mix,” Corrigan says. “But all of the warm mix pavements placed in the field have performed very well.”
To better complete tests on warm mix, they are now trying to find ways to simulate more accurately what type of aging conditions warm mixes are encountering in the field.
“The standardized mixture conditioning procedures for performance testing we conduct in the lab provides warm mixtures that don’t perform as well in a lab setting, but warm mix performs equal to hot mix in the field,” Corrigan says. “We see it as an opportunity to gain a better understanding of how mixtures age in the field and doing a better job replicating it in the laboratory.”
Best practices for producing mixtures
Corrigan stresses the importance of following best practices with all types of mixture including hot mix and warm mix.
“You have to understand what is needed to provide quality material and quality production,” he says. “There are a lot of best practices that have been developed primarily for hot mix, and those are equally, if not more, important for warm mix.”
Some of the best practices include stock pile moisture management or plant baghouse, exhaust gas, fumes, and other air emissions management best practices.
In addition it is important to understand how plants are set up to operate and produce the most efficiently by having heat loses minimized and burners tuned and optimized to run at specific temperature ranges.
“For example, as part of the national research that has been completed we’ve tried to quantify and bench mark the actual emissions and energy savings,” Corrigan says. “What we’ve found is when burners are tuned to operate efficiently at hot mix temperatures, it provides a significant amount of savings when it comes to energy fuel usage as well as reducing emissions to have the burner optimized to operate at that temperature. Similarly, use of warm mix requires changes to the plant to operate efficiently at the lower temperatures.”
While best practices remain important for both WMA and HMA, warm mix production will not cure production issues.
“You need to have best practices already occurring for hot mix to realize all the benefits warm mix can provide to a producer,” Corrigan says. “Savings associated with a properly maintained, insulated, and tuned plant can far outweigh the savings associated with only the usage of a warm mix technology.”
Corrigan is encouraged by the continued success of WMA throughout the country. The partnership of several organizations has helped form a place for WMA in the industry.
“A lot of cooperation as an industry with contractors, producers, federal agencies, state agencies, and academia coming to the table to talk about the issues, the correct way to handle materials, the correct way to use warm mix — that has been a great partnership,” he says.
“We are able to make sure we are doing the best we can to get equivalent performance out of warm mix which has allowed us to implement it in an accelerated fashion,” he concludes. “It’s been faster than we typically would with a new technology in our industry. It has been great to have that partnership and collaboration across the board.”