The flip side of salting winter roads

Nov 05, 2012

Swedish scientists have studied models to help road and bridge maintenance engineers work out how much damage salting the roads in winter might cause to steel-reinforced concrete structures.

As the winter draws in road safety becomes paramount especially in northern climes where icy roads are a perennial problem for motorists. Gritting and salting the roads can help reduce but the use of salt, which contains chloride, comes at a price. Corrosive can penetrate into porous concrete and reach the metal reinforcements within, leading to corrosion after months or years of use.

Luping Tang of the Department of Civil and Environmental Engineering, at Chalmers University of Technology, in Gothenburg, Sweden and his colleague Dr Anders Lindvall of the Central Laboratory, at Thomas Concrete Group AB also in Gothenburg, have looked at the effects of exposure to road salt de-icing over a 10 year and a 25-30 year service period in of chloride ingress into concrete structures. The models simulate heavy traffic moving at speed over such structures.

Writing in the International Journal of Structural Engineering, the team explains that, "Chloride induced corrosion of reinforcement in concrete is still one of the main concerns regarding durability and service life of reinforced concrete structures. Prediction of chloride ingress in concrete is one of the important parts in durability design of reinforced concrete structures exposed to the chloride environments."

Of the two models tested, DuraCrete and ClinConc, the latter is valid against the field data from real concrete road bridges tested after25-30 years of exposure to salting the team says, while the former is adequate for predicting the corrosive effects of chloride after a ten-year period. The study will not only inform those assessing existing reinforced and bridge structures but should allow design engineers to take into account the needs of such structures during the winter months and ensure that they find ways to reduce or even avoid potentially damaging ingress.

Explore further: ESA investigates an alternative, environmental-friendly method of corrosion resistance

More information: "Validation of models for prediction of chloride ingress in concrete exposed in de-icing salt road environment" in Int. J. Structural Engineering, 2013, 4, 86-99

Related Stories

Concrete answers needed for climate change effects

Mar 23, 2011

Understanding how climate change could impact on the deterioration of the basic building block of much of Australia's infrastructure – concrete – is crucial to ensuring major assets such as roads, ...

Tracking down rust

Apr 05, 2010

(PhysOrg.com) -- Damage to concrete bridges caused by rust can have fatal consequences, at worst leading to a total collapse. Now, researchers have developed an early-warning system for rust. Sensor-transponders ...

Bridges get a quick check-up with new imaging technique

Apr 18, 2012

Swiss engineers have developed a new imaging technique that lets them see the insides of massive concrete bridges. Much like a sonogram, this technique provides quick, easy-to-interpret images, so that the ...

Recommended for you

The oscillator that could makeover the mechanical watch

6 hours ago

For the first time in 200 years the heart of the mechanical watch has been reinvented, thereby improving precision and autonomy while making the watch completely silent. EPFL researchers have developed an ...

User comments : 15

Adjust slider to filter visible comments by rank

Display comments: newest first

Moebius
1 / 5 (2) Nov 05, 2012
There is no flip side, just the stupid side. Salting the roads is idiotic and so typical of our ignorant species.
physpuppy
3 / 5 (1) Nov 05, 2012
Not only does it corrode the metal reinforcement, it also damages the concrete, in essence accelerating the process. When the road dries out, the salt recystallizes in crevices and cracks which then further damages the concrete - that's why there are so many potholes during and after winter.
MrVibrating
not rated yet Nov 05, 2012
Hopefully LENR will make electrical deicing economical for such structures before long. But even with conventional power costs, gritting becomes a false economy when the structure has to be closed for weeks due to accelerated aging, as Londoners found out just months before the Olympics. The resulting journey delays probably cost the economy more than the repairs...
gwrede
1 / 5 (2) Nov 05, 2012
A couple of bridges may be a minus in book keeping. The real cost is the millions of car owners. The lifetime of a car is cut in half only because of salting. So the owners get to pay what is essentially what crash insurance companies and the state should pay for.
hemitite
not rated yet Nov 05, 2012
I wonder if putting a negative charge on the rebar would help to keep the chloride ions from reaching the steel?
ValeriaT
not rated yet Nov 05, 2012
The sodium ions are harmful for concrete, as they form a easily soluble salts with silicates, which can destruct the concrete by swelling and expansion during their hydration. The urea is more expensive, but it inhibits the iron corrosion instead due its slightly alkaline nature. It doesn't harm the animals and vegetation and its excess may even serve as a fertilizer. It should be definitely used for salting of roads at bridges and similar metallic constructions, which are prone to corrosion.
I wonder if putting a negative charge on the rebar would help to keep the chloride ions from reaching the steel?
This is essentially what the so-called "wasted anode" approach is about, but it's very expensive.
ka_
not rated yet Nov 05, 2012
Hot sand is much better than salt. The idea was not mine, but the reasoning is really good for why hot sand is better than salt.
1) the reason for using salt is the chemical reaction it has for melting through the ice. The salt will however keep burning itself all the way through the ice and into the asphalt below.
2) Hot sand will just like salt melt the upper layer, but then cool down and stay where it is desired. , whereas hot sand will only burn itself through the surface and STAY where it is wanted.
3) Salt is only effective at close to zero Celsius and will in fact end up making the roads more dangerous once the temperature fall below negative 5-7C. Hot sand on the other hand does not have this problem.
4) Salt destroy not only the roads but cause rust on cars. Sand does not have this problem.
5) The negative side of sand is that it need to be swept away after winter whereas salt burn itself through the asphalt - thus no cleanup.

Tax might be lost as less cars would be sold?
ValeriaT
5 / 5 (1) Nov 05, 2012
The hot sand is not a permanent solution - the salt eutectic solution keeps the snow at roads melted until it's not diluted with another snow and occasionally washed away. The residual sand patches are risky for driving in road curves and the sand is erosive for car chassis at high speed too.
ka_
not rated yet Nov 05, 2012
The salt change the freezing temperature, and will be ineffective if not cause more problems if the temperature drop a few C more. I agree with you that assuming the temperature stay at close to zero temperature, then salt is better, but that is very frequently not the case.
ka_
not rated yet Nov 05, 2012
Quite a few of the areas here in Norway get temperatures below -20C every year. Salt only move the melting point, so instead of the problems arriving at about 0-4C, the salt is seen to move the problem to the time the temperature drop to about negative 5-7 C. But we do not avoid the dangerous effect by salting - it just delay it until it become slightly colder. As temperature drop below 10 there is usually no danger anymore except where the traffic is high at daytime and mostly non-existent at night causing the surface to melt and freeze again regularly.

I do know however that sand is no permanent solution neither, just like salt we would still regularly need to add more. Sand patches may indeed be dangerous as the ice go away, which is why it require more cleanup. however most roads in Scandinavia have logically inclined curves, which mitigate part of the problem assuming you follow the speed limit. I do not know how erosive sand is on a car chassis, but doubt it is as bad as salt.
ka_
not rated yet Nov 05, 2012
I think too little studies have been made to look at the consequence of salting at realistic winter situations. In Norway for example it is typically a 7C difference between city and the surrounding areas. These areas typically all have major traffic. Going further away from the cities and the traffic pattern change. Many roads have hardly any traffic at night but quite a bit of traffic during daytime. In the southern part of the country there are hardly any days or night with below minus 10C, but further north we have days with even minus 40 C and beyond.

I believe we need to use very different methods for different areas. Salt is probably the right choice in some areas, but it is far from a solution that should be used in all those settings.
runrig
not rated yet Nov 06, 2012
As a forcaster for the UKMO in the 90's and early 2000's I routinely gave advice to council winter road maintenance teams. There are roads in the English midlands that are elevated and therefore reinforced. In those cases they would spread Urea. So too did the RAF on their runways. ( I worked with the RAF during the 70's and 80's ).
Eikka
not rated yet Nov 06, 2012
I do not know how erosive sand is on a car chassis, but doubt it is as bad as salt.


The sand is picked up by car tires and it literally sandblasts any protective coating off of the wheelwells and bottom of the car, and it damages the windshield of the car driving behind you. The wet grit can even spray up the sides at speed and strip the paint off the doors. The windshield erosion is particularily annoying, because it makes you blind against any incoming lights or sunshine.

Salt isn't erosive at all, and you can use anti-corrosive coating and galvanizing against it, which will last you a good 20 years when done correctly.

Gritting also doesn't stop the buildup of ice to keep the road flat in the winter. Over time, snow packs onto the road and makes it bumpy. A third alternative is shaving the road which gets rid of the excess ice and leaves a rough surface. The problem of shaving is the damage done to the road surface. If you don't salt, you have to shave.
VendicarD
3 / 5 (1) Nov 06, 2012
Then it must be good for the Economy since it promotes automotive sales and the economic activity needed to replace damaged bridges.

"The lifetime of a car is cut in half only because of salting" - gwerde
Torbjorn_Larsson_OM
not rated yet Nov 11, 2012
Salt is not a problem for cars lifetime/overall economy at the moment, since we need to change them to get to more efficient engines (for cost and for environmental reasons) and winter climate cars are build with it in mind.

Eventually the method will get back to be a major factor for economy. Hopefully we will have other methods by then.

@ Moebius: It saves many lives in statistics, despite moving some of the problem around as ka notes. Which is why it is used in, say, Sweden.

@ MrVibrating: There is no LENR. It isn't even a research field.