Path scholar and honors civil engineering student Piper Fuller met engineering professor Dr. Kevin Hall at a Path Program event during Piper’s first semester at the U of A. She mentioned in passing that she was looking for a job; he mentioned he was in need of assistants in his asphalt lab. And just like that, a partnership was born.
Piper, who wants to pursue a career in environmental engineering, never thought she would end up focusing on transportation. Like most of us, she confesses, “I never thought about the work that goes into making and maintaining asphalt. You just see it on the ground and never think it’s a big deal.” But making asphalt is a big deal: America invests more time and money in pavement than any other element of our civil infrastructure, and once on the ground, the substance is subject to rutting, cracking, pitting and water damage. This is where Dr. Hall comes in: he and his team are working with the Arkansas Department of Transportation to develop a better, more durable asphalt mixture.
Creating and testing asphalt is an unforgiving business, but the heat, sweat, and grime can’t deter Piper. This summer, the second-year student continued her work with Dr. Hall, batching recipe after recipe of asphalt to determine what combination of rock and binder, or what Dr. Hall calls “the black oily sticky stuff,” is most resistant to cracking.
We went out to the lab during the last week of the project, and Piper walked us through the entire process, from sifting pebbles to pressure testing the finished product.
Step 1: Fractionate
“This part gets really dirty,” Piper informs us before she pours a large bucket of rocks into a metal sieve-shaker. This machine separates the rock into 19 different sizes, ranging from typical driveway gravel to a fine, dusty powder.
Step 2: Mix
Once all the rock is separated, Piper measures out a precise recipe of different sizes to use in the aggregate being batched. The team used rocks from six different locations around the state of Arkansas for their pressure tests: here, Piper is measuring out 82 grams of a Russellville grain.
Step 3: Add binder
It’s already hot in the A/C-less lab, but it gets even hotter when it’s time to add the asphalt itself, which becomes liquid at 250 degrees Fahrenheit, and is mixed only once it reaches 300 degrees – researchers must don a full face guard, long sleeves and thick gloves that cover the forearms to prevent injury when mixing. Once suited up, Piper adds a carefully-measured amount of binder to her recipe.
Step 4: Stir
Once the dry ingredients and wet ingredients are combined, it’s time to mix one more time! But not by hand – the mixture goes into a metal bucket, onto which a large, flat stirring paddle is attached.
Step 5: Compact
Compaction is one of the most involved steps in the asphalt-making process: the liquid mixture is poured into a heavy metal cylinder, protected on its ends by pre-cut pieces of paper to prevent the mixture from sticking. The hot, wet mess is poured into the mold, then the cylinder goes into the compactor, which does just what it’s supposed to – it compacts the aggregate into a solid, 160-millimeter-long “pill” of asphalt.
Step 6: Cut
Once the pill is cooled and solid, researchers cut it into two-inch cylinders, and cut those cylinders in half, to be tested for resistance to cracking.
Step 7: Apply pressure
A small notch is made in the flat side of each of the newly-cut half-moon samples, to simulate the beginnings of a naturally-occurring crack. The half-moon is then placed crack-up in a machine that applies a set amount of pressure for a set amount of time. The researchers then observe and calculate the amount of cracking exhibited by the sample after the test. This one doesn’t look like it fared very well…