Jan 22, 2024
In Defense of Segregation
BY Sandy Lender
When suspect material is delivered to your asphalt production facility, do you instruct haul truck drivers to dump it on one large, recycled asphalt product (RAP) stockpile for crushing, screening and manipulation later—probably over the winter months? If you’re blending millings from multiple sources, you might be doing a disservice to your future mix designs.
Let’s look at why.
Depending on the amount of space you have at your site, you want to separate the incoming piles according to their makeup. Given the conversations happening around Per- and Polyfluoroalkyl Substances (PFAS) in airport and other airfield pavements, you’ll likely want those millings to be in a stockpile built on a paved surface, downhill from a waterway, with its own berm around it. Cover it to protect it from rainfall that might encourage chemicals to “escape” and perform testing to ensure any dangerous chemical residue stays below permissible levels.
Please note I’m not condoning segregation of material within the individual pile. Use best stockpile management practices to keep material a homogenous blend going to the weigh bridge, conveyors, drum and so on.
Other stockpiles can be arranged according to nominal maximum aggregate size (NMAS) or the known PG binder in the roadway you milled up. I recognize it’s pie-in-the-sky thinking to believe you’ll know the grade of binder used in the surface you’re taking an inch or two off of, but townships or agencies with good records should be able to tell you, “We paved Elmsview Parkway with a PG68-22 back in 2014 and we’d like to mill and fill it with the same.”
By sorting and—dare I say it—segregating your RAP into multiple piles, you give your future mix design and production team a better chance at superb quality control/quality assurance (QC/QA).
That sounds like a lot of work.
Not every mix incorporating RAP—or even high percentages of RAP—requires exact grading, but when the option is available to you, why not use it? You might as well make the best mix with the most accurate ingredients. You might as well separate your stockpiles into known material versus unknown for those exacting specs and PFAS regulations coming down the line.