Salt vs. Sand

[Tideland Prius]

Hi,

I'm just curious as to the preference of the use of road salt versus sand that cities use on the road. Why would one use salt over sand and vice versa?

[MarinJohn]

sand is more environmentally friendly, still providing traction. Salt melts snow under some conditions, but in the evenings that snow melt turns to ice. salt builds up on the shoulder of the road restricting/killing fauna growth including mature trees.

[MarinJohn]

oops, I mean flora growth

[bookrats]

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oops, I mean flora growth
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Well, salt would probably kill slugs, so I guess flora and fauna both suffer.

[Frank Hudon]

airports use fertilizer to melt ice as it's non-corrosive to aircraft. I suppose in the spring the grass on the medians grows well.

[jayman]

Salt and sand both involve tradeoffs to winter traction, along with health effects and long-term road effects.

Salt is useful to quickly melt slush and ice in moderate temps. This is important at intersections. With roads salted, you can run all-season or lower-traction tires year round, which saves people money.

Salt usually will not work below -30 C. When it's applied to roads and the ice/slush evaporates, the salt residue is left behind, which will dry and be kicked up by other vehicles. Follow a semi on a salt covered road and you'll wonder if you'll ever breathe again.

Salt will, of course, cause corrosion and many cars in the "rust belt" are sent to the crusher long before their time. Of more serious concern to roads and overpasses is the effect of salt on the rebar used in reinforced concrete.

Concrete is porous, so the mixture of water and salt can seep into the cement. A poor cement mix is quickly destroyed by salt, though a properly mixed and properly cured cement is very resistant to salt damage.

Only very recently have rebar been specially coated to resist the effect of road salt. When rebar corrodes, it swells, and this cracks the cement decking. There have been some dramatic overpass failures caused by rebar that has corroded, allowing the deck to drop onto the road below.

Due to the corrosion concerns, salt is never used around aircraft. Usually a combination of plows, sweepers, and hot-air rigs are used to deice runway surfaces. Most transport aircraft can use reversing buckets on jets or Beta pitch on props to assist in slowing down, and the braking system is also anti-skid.

Salt runoff can harm vegetation, but what you really have to worry about is runoff into rivers and lakes where mercury is present. The salt (NaCL) tends to "reactivate" the mercury and you burden the foodchain with mercury all over again.

Sand provides instant traction on slush and "warm" ice. If you get stuck, sand can help get you out especially if there is glare ice underneath. One can make the argument that sand is more environmentally friendly than salt. Sand doesn't cause corrosion to rebar or cement decks.

On very cold ice, unless the sand is pulverized into something resembling talcum powder, it acts like tiny ball bearings and ironically increases the chance of a slide. On dry pavement and especially smooth cement, sand on the road surface is deadly.

Since the ice/snow doesn't melt, you end up with a nasty layer of ice and sand. When it warms up, you get holes in this layer that causes a bone-jarring ride.

Once the spring melt happens, the sand leaves behind a huge mess that has to be cleaned up by street sweeping equipment. It can create dust when driving on the highway.

Most highway departments will spread a mixture of sand and salt, depending on conditions.

[Frank Hudon]

the use of ammonium nitrate fertilzer isn't recommended for use on concrete but for ashpalt streets and such it works good. Only use on a paved drive way not one made of concrete. Other wise it works good. Here on the left coast they only use salt because they don't want sand in the catch basins for the storm sewers. As they drain into the ocean it might raise the salinity of it a bit but I doubt anybody is going to see if they float higer in it or not.

[Tideland Prius]

Wow! thanks for the all the answers. I certainly learned something! Thanks again!

[john1701a]

Sand is completely worthless for keeping roads clear of snow & ice, especially since we literally go for weeks at a time between days where it's warm enough to melt anything.

So here in Minnesota, sand is pretty much used only when traction is needed on clear roads and when it is too late to to wait for the salt to work (an instant solution for ice).

In most all other cases, salt is used. But thankfully, the type with the lowest impact to the environment is used. But that's because Minnesota has a massive budget for keeping roads in top condition... hence the law prohibiting studs.

Anywho, before winter storms here, the roads are pre-salted. To ensure traction before the nasty stuff even has a chance to affect the roads.

[jayman]

The Swedes are also concerned about road safety and keeping their roads in good shape. Rather than ban studs, they re-engineered them.

http://www.nokiantires.com/html/ecostud.html

The biggest problem with using any form of salt on public roads, asides from the environmental effect of salt in our waterways, is the corrosive effect on the rebar used in reinforced concrete. You can use coated rebar, but that's a fairly recent innovation.