Ashburton’s road maintenance contractors are well aware of what has been called the district’s “pothole invasion”.  They’ve outlined to the council what they’re doing to combat it in the face of underfunding, tight budgets and wetter weather. LDR reporter Jonathan Leask digs deeper.

More money.
More resources.
Give us that and we’ll solve the Ashburton District’s pothole problem.
Oh, if only it was that easy.
But that’s a summarised version of what’s needed, and what was explained in more detail to the Ashburton District Council by Harry Alderson, the general manger of roading at HEB Construction.
HEB are a civil engineering construction company charged with the Ashburton District’s roading and pothole maintenance.
Alderson told the council that his contractors were tackling a “pothole invasion” following a wet two-year period and historic underfunding.
Recent extreme weather was also a factor, but Alderson said the “historic levels of investment in perhaps more manageable weather have exacerbated the underlying road condition”.
He said there were 1613km of sealed roads in the Ashburton District network, which were designed to last 25 years, so that would require 60km to be rehabilitated, as he called it, each year.
The average rehabilitation over the past 12 years has been 9.3km, meaning a shortfall of just over 600km of overdue work.
“It’s not because of anyone’s lack of desire to invest at a higher number,” he said.
The historic underinvestment, combined with extreme weather events like the 2021 floods, makes the slow deterioration of the network more obvious, he said.
In the 2022/23 maintenance programme there was 11,600m2 of work being completed, but Alderson said an HEB network assessment identified 59,000m2 “that could do with some help”.
“That’s the balance of investment versus need currently.”
The situation is highlighted by the fact HEB fixed 12,651 potholes in 2022 when the contract was for 6000.
“Anything that we do in terms of an increased number of potholes, or revisiting potholes that might have been done in imperfect conditions through the winter period, is kind of on our tab.
“So we are extremely motivated to be improving the network condition.”
Pothole season is the wet winter period, which Alderson said was just a short-term period to get through until the dry summer months.
“. . . it’s like band-aids at whatever frequency is necessary.”
He said fixing potholes in winter was an almost impossible job because the wet conditions continued to impact any patch repair.
He said a pothole patch was like a runner putting a band-aid on in the rain.
They know it’s not going to stick, and will need to put a proper bandage on it when they are dry.
“Potholes are driven by the presence of water in pavements,’’ he said.
“Pavements are designed to perform in the absence of water.”
Rural roads are built with a base layer of aggregate and 2mm of bitumen, Alderson said.
“That’s the affordable solution for 95 per cent of New Zealand’s roads.
“We are relying on that 2mm to keep it waterproof.”
With heavy rainfall and flooding, even a good surface won’t stop water from getting in and damaging the integrity of the pavement, he said.
With tight budgets being impacted by rising inflation costs, Alderson said it meant “we are asking some of those patches to do more than we should”.
Alderson said the situation was a balance of finding better solutions for the same money.
He said HEB was concentrating on the high-volume roads and refocusing its maintenance to improve water drainage – “things that will protect the network in the long term”.
So, how to fix it?
The obvious solution is a higher level of funding.
Obvious, yes.
But not straightforward because it was constrained by the funding from Waka Kotahi New Zealand Transport Agency, which sets the funding on a three-year cycle.
Ashburton was also not the Lone Ranger when it came to regions and districts needing greater funding from Waka Kotahi.
Ashburton mayor Neil Brown has rightly been frustrated by the lack of funding and the further deterioration of some roads, saying his district’s roading network has been underfunded for a long time.
“We are way under where it should be but that’s all the funding we get.’’
And those years of underfunding was now obvious for all to see.
“. . . we are now seeing the effect of it.’’
With 20 per cent cost escalation from inflation, Brown said there was no extra funding “so it means there is 20 per cent less work which makes it worse”.

The experts respond to armchair critics:

Armchair engineers have suggested using hot mix, concrete or simply doing it right the first time would lead to better pothole and road repair outcomes.
Here’s how the experts responded:

Repeat potholes
HEB’s Ashburton maintenance contract manager, James Faber, said pothole patches were just that – temporary fixes before a full repair can be completed.
“We wouldn’t necessarily have an expectation that a pothole filled would only be filled once,” Faber said.
That’s because the pothole is typically patched “in the weather that has made the problem” and sometimes the patch will hold, but the area around it breaks down.
The repeat repairs are a timing issue between the need for immediate repair and waiting for better weather conditions.
“It is what it is. It’s just a patch,” Faber said.
HEB had been working on trialling different mixes for the pothole repairs to find the best option.
“The one we use now is by far the best, but comes at two-and-a-half times the cost,” Faber said.

Why not hot mix?
Fixing potholes with hot mix could last longer, but it has limitations on its application and some safety risks, according to HEB’s roading general manager Harry Alderson.
“It only stays hot for a limited period of time and so limits our reactionary response,” he said.
“It has a place but has a shelf life where once you have picked it up, you have got maybe a couple of hours to use it effectively in the right places.
“Once it’s cold, it’s far less effective.
“When our teams are out there all day, attending potholes right around the network, we need a product that will be usable at 7am and still usable at 7pm.
“And that’s not hot mix.”
Faber said it’s also a safety risk as it breaks up in clumps.

Why not concrete roads?
Alderson said that how our roads were constructed was “investment by population”, and concrete was not a cost-effective option.
“[Concrete] is a really unsustainable method of construction with the size of our population.”
Concrete is expensive to build and maintain but inexpensive in between, but most areas lack the population density to fund it.
“With a concrete road, once it has achieved its design life there are very limited options to rehabilitate.
“At least with our flexible road environment, we have options to strengthen the road.”

Tar melt
Alderson explained that bitumen would stay soft and was susceptible to tar bleeding for at least two years after resealing. Tar “bleeding” was when the road got hot, causing tar to rise to the top.
The bleeding happens when the binder, usually kerosene and diesel, that was mixed with the bitumen evaporates.
Alderson said when it is applied to the road in a reseal, decisions are made around what mixture will “best make it stick to the road”.
The balancing act is the better it sticks the longer it takes to settle, he said.
The binder used in Canterbury was a softer penetration grade to avoid chip loss during the cold winter months. But as a result, it was susceptible to bleeding during hot weather.
Even a well-designed chip seal could suffer from bleeding if there was a long period of high temperatures associated with heavy vehicle movement, or an increase in traffic volume.

• By Jonathan Leask