Heather Hebson has lived in Brook Hollow subdivision in O’Fallon for 13 years – one of a host of subdivisions that sprouted up on former farmers’ fields over the last 20 years, during the heyday of residential development in St. Charles County.
It’s been a good place to live. The subdivision boasts 91 homes valued between $400,000 to $500,000, not far from the intersection of Bryan and Feise roads, near good schools, stores and other amenities. But now, there is a fly in the ointment, or more accurately, rocks in the shoes of subdivision residents. Sometimes a lot of rocks.
In the last few years, streets in Brook Hollow have begun to fall apart.
Streets have a design life that can be affected by a number of factors – weather, bad concrete, faulty design – problems that are hard to diagnosis.
But in the case of Brook Hollow, authorities suspect a new culprit – “premature pavement failure.” It’s happening on subdivision streets in municipalities all across the county. Concrete slabs, that fit like a puzzle to form streets, are supposed to have a design life of 30 years, but are crumbling after only 10 to 15 years.
What happened to Brook Hollow’s streets may never be exactly known, but authorities are seeing far too many young streets growing old fast. And residents want them fixed.
Asphalt patches and spot repairs delay, but often don’t correct, the problem. And Hebson and her neighbors aren’t in love with asphalt.
“They look terrible, just terrible, horrible,” Hebson said during an O’Fallon City Council work session in November. Hebson is a subdivision trustee. She said Brook Hollow’s streets, particularly Brook Mont Drive, are festooned with asphalt patches.
“It feels like a rollercoaster when you hit it,” Hebson said in a later interview. “It’s like boom, boom, up and down. It can’t be good for our cars.”
A costly compromise
Making repairs is a costly compromise and replacing concrete slabs before their time costs lots of money – money that O’Fallon and other county municipalities are struggling to find. But “premature concrete pavement failure” is now happening at an alarming rate, often in newer subdivisions, in O’Fallon, Wentzville, Lake Saint Louis and St. Peters.
Local city officials are quick to say that most of their subdivision streets – old and new – are in good shape and well-maintained. But early pavement failure presents an unanticipated issue with the potential to balloon street maintenance budgets now and in coming years. And road repair cannot be ignored.
“You have to remember with any municipality, the road infrastructure is the most expensive capital asset that they maintain,” said Steve Bender, O’Fallon’s public works director. “Our road network is estimated to have a value of over $300 million.”
Bender said his city has averaged about $2 million each year on roads and streets, and may spend nearly $4 million in 2017. That cost may increase because maintenance is a constant issue.
Wentzville City Administrator David Gipson said slab failure rates are citywide, in nearly every fairly new subdivision development. Like O’Fallon,
the city has a robust slab replacement program and has been budgeting about $2 million annually for street repairs.
“With budgetary constraints, I think that that’s a number that is going to remain pretty constant and I don’t see that easing up really anytime soon,” Gipson said. “I would say definitely for the next five to 10 years, we’re looking at $2 million a year in slab replacements just trying to keep up with the problems.”
Gipson, Bender and other officials are grappling with what happened and how to remedy the situation. Local cities are forming what they are calling the “Eastern Missouri Pavement Consortium.” The group is modeled after a similar effort in the Kansas City area.
The consortium is expected to review concrete mix designs and the rock, sand or gravel mix known as “aggregate” that is used to make concrete and develop procedures and standards. O’Fallon and Lake Saint Louis are among the municipalities who have signed off on the agreement authorizing the consortium. St. Peters and Wentzville aldermen are expected to review the agreement in January.
But the haunting question remains: What caused the concrete to crumble?
A perfect storm
The cause may have been a combination of human failure and bad rock.
Perhaps there was less oversight regarding how some concrete was made or maybe rock from the wrong pile was used in mixing concrete at quarries. Perhaps it was simply a problem with the rock itself.
“I think it was more a geological problem than anything else,” Gipson said.
Concrete is a mixture of aggregate [rock, sand and gravel] mixed with water and Portland cement. The chemical reaction hardens the material. Streets are often laid out in 13- by 16-foot slabs. When those slabs fail, they crack and crumble.
Wade Montgomery, O’Fallon’s city engineer, said city staff started noticing cracking a few years ago, often starting at joints of slabs and eventually causing flacking and crumbling along the surface of the street.
Cracking can be repaired. Often, it can hold up. But city street officials were finding more slabs in relatively new subdivisions deteriorating quickly. Repairs only seemed to delay the problem. Within a year or two, cracking often moving over to the next joint. A real fix meant digging out the slabs and pouring more concrete. That fix is expensive.
O’Fallon and other municipalities brought in industry experts, such as the American Concrete Pavement Association [ACPA] and Iowa State University, to discuss the problem. Still, finding a direct cause remained elusive.
Montgomery said different contractors using different quarries were used, making it difficult to trace back a source of bad concrete.
Investigations did find some potential causes – concrete mix designs that hadn’t been reviewed or were reviewed by people without a lot of experience; too much water or not enough air also may have been a factor along with poor finishing or curing techniques. Bender said the investigations are ongoing.
More often, what the investigations have come back to is the rock that was used. O’Fallon took core samples from several streets and found a surprise – alkali reactive rock. Alkali reactions – particularly an alkali carbonite reaction [ACR] involving some forms of limestone – often prompt concrete to expand and break apart.
To say that alkali carbonite reactions are rare in this part of the country is an understatement said Ken Liecheit, field engineer with ACPA. Up until now, alkali carbonite issues haven’t been found here, he said. “We’re blessed, on the east side of the state, we have some of the best limestone in the country.”
Liecheit said he sees a number of potential contributing factors for pavement failures. Some may involve changes in testing criteria by the Missouri Department of Transportation [MoDOT], prompted by a lack of funding, and whether specifications were followed by cities when rock was used.
“You can state what you want all day, but if you don’t watch sometimes, or check what stockpiles it [rock] was taken out of, you can’t guarantee that you’re going to get what you want,” he said.
The answer may be as simple as some bad rock got into the system, perhaps from a ledge of material that was dug out of a quarry. “I think that ledge is already gone,” Liecheit said.
He said a careless operator may have loaded the wrong pile of rocks, but “it’s hard to say. When you had a lot of construction 10 years ago, material was in demand.”
Getting a fix on the problem
Alkali reactions aren’t an easy fix. But the hope is that the Eastern Missouri Pavement Consortium will be able to help in finding answers and develop preventative procedures.
Bender told the O’Fallon City Council in December that a collective effort, involving local governments, may develop common and consistent specifications, which will reduce headaches for developers and builders and improve the quality of concrete projects.
The Kansas City Metro Materials Board is a model that has been in existence 10 years and includes 19 agencies, he said. Consortium members will pay a sliding scale from $4,000 for small cities to up to $16,000 for large cities annually. And it may not be limited to St. Charles County.
Bender said the consortium may be open to other local governments and agencies.
“We’re not experiencing that problem,” said Chesterfield City Administrator Michael Geisel, noting that the city’s specifications may be different. The city rarely does what the industry calls “postage stamp style replacement” where one slap here or there is replaced, he said.
Geisel said Chesterfield likes to do entire blocks or lengths of street and also prefers to use concrete rather than asphalt to make other repairs. “They [asphalt and concrete] just don’t work well with each other,” he said.
Hebson said the residents of Brook Hollow subdivision agree – and she added a concern beyond bumpy streets.
“It’s having an effect on our home values. One of the neighbors asked me, if we had some siding that was blown off in a hurricane or a storm or something, what would be replace it with? The same siding. So that’s what we’re asking the streets get fixed with, the same kind of look they should have, and not the asphalt on concrete,” she told the O’Fallon City Council.
But for now, patchwork pavement might be the best local cities can do.