Nonprofit, nonpartisan journalism. Supported by readers.

Donate

It’s pothole-filling time. So where does the asphalt come from?

Asphalt Plant
MinnPost photo by Bill Lindeke
Every few minutes, a lever is pulled somewhere in the tower house and hot, fresh asphalt descends from a hot bin into a waiting truck bed like a waterfall of black tar.

Each morning in the early spring, the line for fresh asphalt extends for a half-mile down Topping Street in St. Paul’s North End neighborhood. Just past Como Avenue and east of Dale Street, among the warehouses and light industrial garages, dump trucks from nearly every municipality, county, township, or private paving enterprise idle along this quiet back road, waiting for the metro’s only supplier of hot mix asphalt to make their daily batch of tar.

The city’s Municipal Asphalt Plant is a 55-year-old structure that towers impressively over the ball fields and skate park on Front Avenue. When I lived nearby, I remember gazing at the old steel structure and wondering about its origins. The tall smokestack and rusty steel girders form a dramatic industrial backdrop for Little League teams and skateboarders who use the next-door Front Park at all hours of the day.

This is to say that the asphalt plant is an unromantic sight. A maze of grimy steel railings, steps, conveyors, and massive tanks coated with an oily sheen rises up like something out of the 19th century. Approach and the unmistakably dank scent of petroleum fills the air and curls your lip while the dull whirr of the giant steel drying bin revolving on its axis drones and the conveyor belt mechanically trundles high into the air. The sounds of the yellow front-end loader interrupt the din, along with the low idling of a dozen diesel trucks waiting for their turn under the machine. Then every few minutes, a lever is pulled somewhere in the tower house and hot, fresh asphalt descends from a hot bin into a waiting truck bed like a waterfall of black tar.

“Every day something different is going to happen,” says Cicely T. Schurhamer, who has been the plant manager for the last 15 years, keeping the giant machine humming along. “Something different is gonna break every single day. It’s a simple process, but the machine is very complex.”


It’s safe to say that most people take their roads for granted, at least until they aren’t plowed properly or the potholes menace a fragile suspension. But underneath every inch of a rubber tire is some form of aging asphalt or concrete, and all that asphalt is made right here between Topping and Burgess Streets.

A veritable menu of blacktop

The complex is the last city-owned asphalt factory in the metro, and the only “batch plant” that can flexibly mix asphalt at small scales. That’s why Schurhamer offers a veritable menu of blacktop, and can provide all kinds of different asphalts for different paving purposes.

“We make quite a few different mixes,” she explained. “We can use different amounts of oil, and different sizes of aggregate.”

Municipal Asphalt Plant
MinnPost photo by Bill Lindeke
The city’s Municipal Asphalt Plant is a 55-year-old structure that towers impressively over the ball fields and skate park on Front Avenue.
Here’s how the plant works: One of the Public Works employees uses a giant yellow front-end loader to shovel aggregate into a pit just underneath the ground’s surface where it lands on a series of six Syntrons, machines that vibrate to agitate the aggregate, loosening it and moving it toward the conveyor belt. The belt then takes the aggregate up into a massive rotating steel drum that heats and dries out the material.

At this point the dust separates from the larger material — in the case of current pothole asphalt mix, the aggregate is BA modified .5″ minus, meaning all the particles are less than a half-inch in diameter — and the dust rises into cyclonic collector to help offset any particulate pollution. The dust goes through a “wet scrubber” and then down into a settling pond that lies next to the machine, where steam rises from the hot rectangular pools.

Elevator to the ‘hot bins’

Meanwhile, the heated, dried aggregate hits another elevator that takes it into the “hot bins” at the top of the asphalt machine. At this point, the tiny rocks mix with the oily black asphalt cement from the storage tanks on the other side. After each of the clients punches a code into a keypad and makes a specific asphalt order, the plant operator waiting in the room at the top drops the now-hot mix into the waiting truck below.

(Fun fact: the Public Works employees take turns at each of the plant’s stations, rotating through the week, so everyone gets a turn operating the hot bin.)

The whole thing hums along from 7 a.m. until just before noon, with trucks sometimes lining up almost an hour before the plant opens to be the first in line.

Schurhamer has been working at the city for almost 30 years. During that time she’s attended plant conferences and dozens of asphalt cooking classes, part of the MnDOT certification process. She admitted she gets requests from frustrated drivers for special pothole fill on their pet roads, but there’s nothing she can do about the state of city roads that she’s not already doing.


The demand for asphalt is intense, and the plant goes through five truckloads of aggregate every day during the busy season, most of it shipped up from pits near Rosemount or Hastings. In August, the plant makes a different kind of asphalt from harder St. Cloud granite, useful for longer-term “mill and overlay” paving that can handle the pressure of larger traffic volumes.

The plant’s tanks contain two different types of oils, both delivered from the Flint Hills Rosemount refinery and pumped into the holding tanks. In the summer the plant uses a performance grade oil cement called PG 64S-22. (The numbers refer to the temperatures of the asphalt mix within which the pavement should be applied.) In the winter, the cement is a so-called slow cure “cold mix” using a cement called SC-800.

Municipal Asphalt Plant
MinnPost photo by Bill Lindeke
A maze of grimy steel railings, steps, conveyors, and massive tanks coated with an oily sheen rises up like something out of the 19th century.
“We’ll make some in October and people will come pick it up, and save it all winter long,” Schurhamer explained. “It’s very busy when we first open because the other plants aren’t open yet.”

(The slow curing of the cold mix does not make for a very good pothole solution, which is why cities are so desperate for the longer-lasting hot mix when it first appears in the spring.)

‘Batch plant’ is flexible

With different combinations of oil and aggregate, the “batch plant” is flexible compared to the bigger commercial asphalt producers that contract out for city or municipal jobs.

The daily grind of making asphalt is one that, much like baking bread, leads to an early-morning schedule. “I usually get up at 4,” Schurhamer explained, in order to meet demand from the dozens of pothole patching crews around the metro area.

“These guys have been coming in early too,” she continued. “They’ve been getting here around 6.”

Watching the parade of pothole trucks go by is a great way to experience the variety of governmental logos in the metro area. In just a few minutes, trucks from Sherburne, Hennepin, and Washington Counties pass under the asphalt tower and receive their morning asphalt tar, along with the cities of Lino Lakes, Blaine, East Bethel, and a dozen more.


(Another fun fact: The best logo of the bunch belongs to Blaine, which has a sort of 1980s vibe.)

For the rest of the year, St. Paul keeps the plant going for its own needs and internal pavement considerations. Due to the vagaries of civic investments, the city is not allowed to bid for work in cases where there is a competitive bidding process, so the busy season dies down a bit once commercial asphalt manufacturers open up in the summer.

The factory is a bit of an anachronism, as the aging complex is the last municipally owned plant in the Twin Cities.

First to open, last to close down

“We’re the first to open and the last to close down,” says Lisa Heibert, the Public Works spokesperson. “If you see any potholes being filled anywhere in the Twin Cities right now, its coming from here.” The seasons of asphalt ebb and flow with the changing of the calendar. In the off-season, from January to March, the plant is idle and undergoes maintenance, but then things pick up steam.

This last year, the city of St. Paul spent about $600,000 to acquire a new fix steel drum from the same company in Washington state that built the plant originally back in the ’60s. According to Schurhamer, the old drum was so worn and patched that “you could actually see the holes.” The new drum, made from AR high-resistance steel, is expected to last a lot longer.

“A lot has to be maintained,” Schurhamer said. “There are so many parts, bearings, pumps, so many things that can go wrong.”

Municipal Asphalt Plant
MinnPost photo by Bill Lindeke
The complex is the last city-owned asphalt factory in the metro, and the only “batch plant” that can flexibly mix asphalt at small scales.
The same is true for the asphalt, of course. On average, a fresh layer of road pavement lasts seven years until it’s worn down to the point where it needs to be re-mixed and re-paved again. With more than 1,800 miles of city-owned streets to continue to pave, that makes the plant and Schurhamer’s jobs a bit Sisyphean. By the time the seven-year cycle is complete, it needs to be begun again, so that creating the city’s supply of asphalt is rather like pushing an endless aggregate rock up a conveyor belt forever.

This time of year, though, the new asphalt is welcome news as one by one, on every street in the metro area, asphalt from the weather-beaten North End factory spreads out by the truckload to fill the potholes of the Twin Cities. The fragile suspensions of a million drivers are in its debt.

You can also learn about all our free newsletter options.

Comments (6)

  1. Submitted by Dennis Litfin on 04/02/2019 - 11:33 am.

    Great article…thanks.

  2. Submitted by Mark Kulda on 04/02/2019 - 12:31 pm.

    What a very helpful, informative and interesting story! Thanks!

  3. Submitted by Frank Phelan on 04/02/2019 - 03:09 pm.

    Sounds like government is filling a need the private sector has utterly failed at.

    Who knew?

  4. Submitted by Mark Voorhees on 04/02/2019 - 05:08 pm.

    Good article. Thanks

  5. Submitted by Tom Crain on 04/02/2019 - 05:11 pm.

    View slideshow about the asphalt plant here
    https://www.stpaul.gov/departments/public-works/street-maintenance/asphalt-plant

  6. Submitted by Brian Simon on 04/03/2019 - 12:23 pm.

    Bill, if you’re up for digging up some more obscura, what to they do with street sweepings?

Leave a Reply