Jun 22, 2019
Make WMA Relatively Hot
BY Sandy Lender
I tend to enjoy the high temperatures in Florida. Sure, it gets hot and humid here, but my definition of hot may not be the same as someone who lives closer to the equator or in Arizona. When the ambient temperature is 95 degrees F here, my neighbors may be complaining, I’m watering plants like mad, and someone in Quito or Tucson is probably wishing for that kind of break in the heat.
The same is true of asphalt pavement mix temps. If you have a plant producing mix at 230oF, someone who is not familiar with our industry might consider that hot.
In fact, that temperature is smack in the middle of the range for a warm-mix asphalt (WMA), which is the theme of this month’s issue. If you check with the Federal Highway Administration’s Every Day Counts program, the range for WMA is 30 to 120oF lower than traditional hot-mix asphalt (HMA) temps. Other sources have a “more slender” range of 30 to 75oF lower than traditional HMA, but the point is that WMA is, by definition, made at cooler-than-traditional mix production temperatures.
Whether you produce the WMA by mechanical foaming or by introduction of a WMA additive, the definition of warm mix includes a designation of “lower” temperature. By dialing down the production temperature, the asphalt mix producer gives himself a host of benefits at the plant, including reduced fuel use and reduced stack emissions. The mix itself offers benefits at the paving site, including worker comfort and improved compaction.
Benefits get discussed throughout this edition of AsphaltPro, so let’s stay focused on temperature for this note.
If you find yourself tempted to introduce a WMA additive to your production process, yet leave your production temperature up around 300 or 310oF, you are not making a warm mix. You’re making an HMA with a WMA additive. If you find yourself tempted to foam your HMA with water or additives, yet leave your production temperature up around 300 or 310oF, you are not making a warm mix. You’re foaming HMA. You may get to enjoy compaction benefits at the paving site, but you’re not enjoying benefits at the plant, are you?
You’re not making conditions more comfortable for workers anywhere. There’s no reduced fuel consumption or reduced emissions when you’re still running at 320 and up.
The point is this: WMA is cooler than HMA.