The recent collapse of a 58-year-old bridge in Washington state along the well-traveled Interstate 5 corridor has drawn attention to aging infrastructure in the U.S., sparking discussion about how the nation’s bridges are maintained.
In Alaska, the challenges of bridge maintenance are even more extreme. Wildly fluctuating temperatures and weather, studded tires and heaving ground make Alaska’s roadways even more vulnerable to wear and tear. Now, an Anchorage-based company has patented a unique method of spreading a material that’s thousands of years old, but has fascinating implications for road maintenance projects in Alaska and nationwide.
For years, Magnesium Phosphate Cement (MPC) has been used for small patches on roads, runways and bridges. Usually, it comes in small bags or buckets out of necessity -- the material sets up extremely quickly, allowing a vehicle to be driven over it in about an hour during normal curing conditions. It’s water resistant, unlike porous concrete, which means MPC doesn’t have the expansion and contraction issues that accompany the freeze-thaw cycle, causing premature wear.
But it’s a tricky substance, too: It can’t be used in traditional cement trucks because it will bond to the walls of the rotating mixer on the back of the truck, solidifying despite constant rotation and likely tipping the vehicle over.
It’s also about twice as expensive as traditional cement, though the working life of MPC is much longer, too. So for years, it’s only been used in small quantities to patch small problems.
Innovative Alaska brothers
Last fall, though, the Alaska Department of Transportation allowed Anchorage-based company APUN to conduct a bit of an experiment on a 243-foot-long bridge over Portage Creek, south of Alaska’s largest community along the Seward Highway. Riddled with pockmarks and grooves from years of wear and tear on its concrete surface, the bridge was in need of resurfacing.
Brothers Rob and Donell Bond of APUN, a family-owned company in Anchorage, had developed a method to quickly mix large quantities of the powdered magnesium and liquid phosphate needed to cover a much larger area of roadway with MPC more quickly than ever before.
Instead of the usual process for resurfacing concrete, which can take days or weeks -- inconveniencing drivers and driving up labor costs while the top layer of the old concrete is ground down and the new concrete cures -- the entire Portage Bridge project was done in less than a day.
It was a bit of trial and error at first, admits Rob Bond, who said it took about 12 hours to complete the first lane of the road. After the kinks in the largely-untested system were worked out, the second lane of the bridge was completed in about three hours, he said.
The end result? In the space of a (long) workday, the entire surface of the bridge was again ready for traffic and planners hoped it would stay that way for more than a decade.
Not a new material
Magnesium Phosphate Cement is not a new idea, it’s just taken a back seat to the more widely-used “Portland cement” that’s been the norm in construction for more than a century, said Rob Harper, a spokesman for Institute of Northern Engineering at the University of Alaska Fairbanks.
“This stuff was invented toward the beginning of the Industrial Revolution,” Harper said of the traditional cement. “The idea was to invent this to keep pace with industrial development at the time.”
Portland cement is primarily made up of the regularly available mineral limestone, which is easily found and processed. When combined with water, the limestone mixture becomes a sloppy powder that eventually crystallizes into the stuff that we drive our cars over.
The initial appeal of Portland cement was the fact that it was activated by water, Harper said. But even then, that cheap method of activation had a downside.
“Especially in Alaska, concrete’s No. 1 enemy is water,” Harper said. “Even though Portland cement was originally more attractive because it was activated by water, over time that’s also been its downfall.”
MPC can be harder to come by. There are only a few magnesium mines in North America, said Rob Bond. And its use in industrial applications has been stunted a bit by the material’s quick-drying nature.`
Biggest selling point, biggest hindrance
At his shop on Friday, Rob Bond spread a small batch of mixed MPC over a spot on the concrete floor. Forty-five minutes later, he drove over it with a forklift, leaving only a slight tread mark and peeling up one small edge that was still a little soft. Another fifteen minutes, and you could expect to drive a car over it without any damage, he said.
While the quick-drying feature of MPC may be its biggest selling point, it’s also its biggest hindrance -- and likely why wider uses have gone largely unexplored. Previously, to spread a lot of MPC -- say enough to cover a 243-foot-long bridge -- you’d need an army of laborers on their hands and knees working with trowels, while another group mixes batches of MPC in hopes it can be spread before solidifying.
Enter APUN. With an elaborate setup on the back of a trailer terminating in a spigot where the MPC comes out, the Bonds have created a way to patch potholes quickly with MPC. And with a larger attachment based on the same principle, the company completed last year’s bridge project with relatively few workers.
“The equipment is really the innovation,” said Donell Bond. “Magnesium phosphate materials were used on the Great Wall of China. These materials have already been in use for thousands of years.”
APUN has merely come up with a way to spread a lot more of it a lot more quickly. The larger dispenser can put out 10 to 20 tons of MPC per hour, Rob said.
Looking back, moving forward
The Alaska DOT has been interested in the potential applications for MPC for decades. In the 1990s, they conducted experiments with the material on bridges along the Dalton Highway. That mixture, intended to be capable of holding a vehicle after only 45 minutes, was delivered in bulk packages of 4,000 pounds.
There are still downsides to APUN’s fast-spreading MPC system -- the up-front cost for MPC is about 20 cents per square foot, twice that of traditional concrete. And because the system is so new, there are still lessons to be learned. The Portage Bridge project was a sole-source bid in order to allow APUN to test its new technique, but Rob Bond said his company still lost money on it.
The more that the Bond brothers and their crew get to use the method, the easier they expect the whole process will become. That’s evident even from the time it took to finish each lane of the Portage Bridge last year.
And even with that upfront cost, with the tighter bond of MPC versus traditional concrete, the working life of the material is expected to be up to 10 times longer than Portland cement. And that fits in with MAP-21 -- a massive highway funding act signed into law by President Barack Obama last year -- which rewards innovation and promotes longevity in the nation’s road projects. If APUN's method bears out over the long term, the option may become an increasingly attractive one
With that in mind, Rob said that the Alaska DOT is looking at a few other bridge resurfacing projects this summer using the APUN method. But DOT representatives said that the Department is moving forward cautiously, since APUN's method is still untested in long term applications. Todd Vanhove, a maintenance specialist with the DOT who was involved with last year's Portage Bridge project, said that another full-bridge project in 2013 is "unlikely" given the untested nature of this new application method. Still, he said, the DOT is "hesitantly" optimistic about MPC's potential for future applications.
"...Mainly because of the cost, and the unknown wear factor," Vanhove said of the department's uncertainty. "But as far as the way the product lays down and the results we’re seeing so far," the method has shown promise.
DOT spokesman Rick Feller expanded on that idea. "I think overall, we just don’t know yet," Feller said. "There are some long-term performance questions, so we're taking a cautious approach to this and want to be comfortable before we go to a wider spread application ... make sure it’s cost-effective over time."
Vanhove said that the department has met with APUN in hopes of conducting a better-controlled and better-documented application of the material in order to further determine MPC's widespread applications.
Additionally, the company is in talks with the DOT in the state of Hawaii to spread MPC on the heavily-traveled Interstate H-1 on the island of Oahu. That road, Rob said, is too busy to shut down more than one lane at a time, ideally at night, making MPC a good fit for proposed repairs.
Meantime, the Bonds are staying busy, and Rob took a trip up to Nenana Monday with the smaller pothole-patching MPC spreader to do some spot work.
And if you’ve been eyeing some chipped spots on your back patio and are looking for a quick fix, you can also buy MPC for personal use. Just be sure to work quickly.
Contact Ben Anderson at ben(at)alaskadispatch.com