As if Nebraska’s extreme temperatures and liberal use of road salt weren’t hard enough on our highways and byways, the sand and gravel aggregate used to make concrete across the state carries in it the seeds of its own destruction.

Silica in the region’s gravel reacts badly with the alkali in Portland cement after they are combined to make concrete for paving. The chemical reaction creates a gel underneath the surface, which expands when it gets wet in summer thunderstorms or winter snows.

The mushrooming gel squeezes the pavement from inside and causes it to crack, especially at the joints. The telltale signs are gray or black splotches emanating from those joints.

“They call it cancer inside concrete,” said Jiong Hu, a University of Nebraska-Lincoln engineering professor who studies the composition of concrete. “Eventually, the whole slab crumbles.”

Alkali-silica reaction (known in the industry as ASR) has been documented in a majority of states, but Nebraska seems to be ASR’s ground zero.

That’s because the Platte River gravel used for concrete in the most populated parts of the state, from Omaha to Scottsbluff, is especially high in silica, which is one of the most common minerals in the Earth’s crust. Glass, beach sand, silicone and granite are all silica materials.

“You don’t have this everywhere. Unfortunately, Nebraska is one of those places where you do,” Hu said.

Grand Island street Superintendent Shannon Callahan confirmed that streets in Grand Island have the ASR issue; one of the roads was Highway 2, which had to be replaced because it quickly deteriorated.

Because officials know of the risk factor, Callahan said, they are taking measures to correct the mixture so that new Grand Island streets don’t set off the ASR reaction.

Along the Platte River basin, the silica level gets higher as you move east toward the Missouri River, said Bruce Grupe, executive director of the Nebraska Concrete Paving Association, an industry group.

“Omaha’s about as reactive as it gets,” he said.

ASR has contributed “significantly” to the deterioration of the city’s streets, said Austin Rowser, Omaha’s deputy public works director. It can worsen seasonal potholes and lead to the collapse of entire sections of roadway.

The most notorious example happened in 2019 — which could be remembered as Omaha’s Pothole Year from Hell. A snowy and frigid February followed by a sudden March thaw (and the state’s worst-ever flood) led to the complete failure of 144th Street from Q Street to Millard Avenue.

The road was so bad, the city closed it completely and rebuilt it — only 13 years after it had last been paved.

Cutting fly ash out of road mix? Big mistake

Rowser said the problem appears to be worse in roads paved between 2000 and 2015, for reasons that still aren’t completely clear — though it roughly coincides with the time that the city quit adding fly ash to its standard concrete mix.

Fly ash is the residue left over after coal is burned in coal-fired power plants. Since the 1980s, the federal government has encouraged its use in paving concrete in what seemed like a win-win: adding fly ash slowed the progress of ASR in finished pavement, and it disposed of a messy byproduct of coal-burning that otherwise would be buried in landfills.

“We really kind of used that stuff pretty heavily with the understanding that it would mitigate (ASR),” said Grupe, formerly the city engineer in Kearney. “It helped in the short-term.”

But over time, some forms of fly ash seemed to actually make ASR worse. That prompted Omaha to eliminate fly ash from its concrete in 1996.

Big mistake. “We saw (ASR) accelerated after we quit using fly ash,” Rowser said.

Douglas County Engineer Todd Pfitzer said much of the newer concrete is in worse shape than pavement poured decades earlier.

“Our concrete now is arguably worse than it was 50 years ago,” he said. “Concrete should last 25 to 50 years. We’ve got concrete that’s 10 years old that looks terrible already.”

Omaha did bring back fly ash in 2015, Rowser said, using a different kind (called Class F fly ash) that seems to work better.

Last year, the city surveyed 422 lane-miles of both major arteries and local streets paved between 2000 and 2015. All but 46 lane-miles had some signs of ASR-related cracking.

None were rated in “poor” condition, defined by extensive cracks and ruts and severe potholing. Rowser said the city takes corrective action before a road deteriorates that badly.

But 32 miles were rated only “fair.” These are roads that show moderate to severe disintegration of the road surface (called raveling) and significant cracking with shallow ruts.

The lowest-rated roads were mostly smaller, local ones.

But several stretches of major roads rated only fair, too:

--Blondo Street from 132nd to 135th Street, paved in 2002.

--72nd Street from Dodge Street to Cass Street, paved in 2001.

--Millard Avenue from 144th Street to Q Street, paved in 2006.

--Jefferson Street from 180th to 183rd Street, paved in 2002.

--L Street from 111th to 120th Street, paved in 2008.

Blondo Street from 132nd to 135th Street, paved in 2002. 72nd Street from Dodge Street to Cass Street, paved in 2001. Millard Avenue from 144th Street to Q Street, paved in 2006. Jefferson Street from 180th to 183rd Street, paved in 2002. L Street from 111th to 120th Street, paved in 2008.

Rowser said some panels of the Blondo, 72nd and Fort Street segments have been replaced. The Fort stretch, now riddled with potholes, has a checkered history.

The original four-laning of Fort Street between 108th and 120th Streets in 2002 was plagued with delays and shoddy construction. Work stretched on for three years, and the contractor was forced to make repairs after sections of the road dipped and the pavement cracked. The World-Herald described motorists’ “hubcap-rattling ride” over the then-new road.

A major overhaul of Fort Street is a priority for Omaha Public Works and City Council member Aimee Melton, who represents the area. The street is expected to be a candidate for funding in the next year or two, Rowser said.

The concrete cancer is ‘a headache for us all’

Coming up with the right concrete formula is a tricky process, one the city and the Nebraska Department of Transportation have wrestled with for years.

Broadly speaking, Grupe said, concrete is made up of roughly equal parts aggregate (sand and gravel), powdery Portland cement, and limestone — which, along with fly ash, lessens the effects of ASR.

After several years of working with the Nebraska Concrete Paving Association, the road construction industry and sand and gravel suppliers, the City of Omaha recently approved a new concrete formula that officials believe will boost the durability.

Grupe said the new formula uses less cement and aggregate while increasing limestone.

“We have very high hopes that this is going to perform better,” Pfitzer said.

Omaha’s problem is that, even with a new concrete formula, it is still stuck with at least 20 years’ worth of cancerous roads that will inevitably self-destruct.

The only way to prevent ASR completely is to use sand and gravel that is low in silica. Unfortunately, that is hard to find around here, since high silica levels are common in surrounding states, too.

“It becomes cost-prohibitive to truck it from someplace else,” Hu said.

The right maintenance can stretch the life of concrete. That means regularly sealing joints in the road. They are the weak link where water is most likely to penetrate — and the place where potholes generally form first.

“It’s awfully important to keep the joints sealed,” Grupe said.

Overlaying affected roads with asphalt smooths things over, but only for a while. The reaction still continues below the surface and will ultimately undermine the road.

The solution remains elusive. Scientists and engineers are likely keep tweaking their formulas, grappling with self-destructive concrete far into the future.

“The silica stuff has been a headache for all of us,” Pfitzer said. “I wish I knew how to make it go away forever.”

Lincoln — 33rd/Cornhusker Viaduct ($66,706,880)

The project was selected for Final Design, Right-of-Way Acquisition and Construction and includes activities to eliminate two at-grade crossings in Lincoln. It will build a new bridge over the rail corridor to eliminate two at-grade railroad crossings at N. 33rd and Adams streets.

Grand Island — Grand Island Rail Crossing Study ($600,000)

The planning project was selected as a prioritized Corridor Improvement Plan for 17 rail crossings in Grand Island. The project recommends crossing closures, grade separations and targeted safety countermeasures to enhance safety and address unreliable travel routes and emergency response delays caused by frequent train traffic.

NDOT — Omaha to Lincoln Rail Crossing Study ($600,000)

The proposed project was selected for Project Planning and includes activities to evaluate 73 at grade crossings along 64.5 miles of BNSF track across Nebraska. The project will identify various safety improvements, including crossing closures, installation of active warning devices, realignment of crossings, upgrades to grade crossings and new roadway connections.

“This is wonderful news for Nebraska,” said NDOT Local Assistance Division Manager Jodi Gibson. “We want to congratulate and thank our partners including the City of Lincoln and the City of Grand Island for their initiative and efforts in applying for these grant funds. The selected projects will eliminate the risk of collisions which delay drivers and emergency responders and most importantly, save lives. We also want to share our appreciation for BNSF and their support in the successful grant applications and these projects that will provide for a safer rail network for Nebraska.”

“An investment this large, over $67 million, will make a significant impact to the safety and efficiency of Nebraska’s transportation system,” said NDOT Director Vicki Kramer. “Railroad crossings present a vulnerability, and the funding will allow Lincoln and Grand Island to address their local needs while the funds awarded to NDOT will focus on the 73 crossings between Omaha and Lincoln. I appreciate BNSF’s partnership in addressing rail safety in Nebraska and the Pillen Administration’s support to enhance our grant application processes, these funds are a step forward in identifying, designing and building a safer, stronger more efficient network.”

The Nebraska Infrastructure Hub looks forward to securing more of this critical funding to Nebraska through providing support to state and local partners to, more confidently, navigate the challenges of the application and administration processes.

Learn more about the RCE Grant Program at railroads.dot.gov/grants-loans/railroad-crossing-elimination-grant-program, and find additional details on Nebraska’s grant recipients and other states’ awards railroads.dot.gov/FY23-24-RCE-Grant-Program-Selections.

Go to the Nebraska Infrastructure Hub website to learn more at dot.nebraska.gov/business-center/nebraska-infrastructure-hub.