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?
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.
<div class='quotetop'>QUOTE(MarinJohn\";p=\"63921)</div> Well, salt would probably kill slugs, so I guess flora and fauna both suffer.
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.
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.
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.
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.
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.
Some places around here are experimenting with this product: Magic Salt. I have not heard their results yet. I like to see efforts to reduce salt usage as much as possible. It's very hard on the environment, bridges, and cars. I believe that my own cars would last twice as long if they didn't rust away when they do. That's about $1000 per year per car right there.
The "magic salt" sounds interesting. I think a lot of organic and safe technologies have faded away due to large corporations pushing false and misleading statements, to deliberately ruin the product and ensure their profits. Look how GM managed to keep subways from LA for so long. They had obvious reasons to encourage the Car Culture. An inventor here in Winnipeg developed a very safe and effective enzyme that when sprayed on gravel roads with high clay content, created a road surface much harder than pavement and longer lasting, at a miniscule fraction of the cost of paving. Sadly, this inventor has only had success in Third World nations. Asides from a handful of municipalities here in Manitoba doing "trials" of his product, there have been no serious takers. http://www.cypherltd.com http://www.cypherltd.com/earthzyme.php It seems the large corps have a strong vested interest to ensure we only use "proven" aka high cost solutions. About the only problem I can see with using the molasses leftover on roads is a problem we already have in winter with salt: deer will venture onto the roads to lick the salt. I imagine a lot of animals would want to snack on that sweet residue left behind by the molasses mash. I suppose if I was on a long, boring drive and needed a quick sugary pick-me-up, the Magic Salt would be just the ticket. Just have to watch out for oncoming traffic ...
Several highway departments and national parks use a mixture of sand and cinders. Cinders absorb insolation and match the albedo (reflectivity) of asphalt. Sand provides traction. Worst negative effect: dust storms during mud season (prolonged spring) when temperatures daily move from below freezing to above and back to below again. Salts are never acceptable - they change soil and water pH and conductivity, corrode metal, wood and concrete and adversely affect vegetation, soils and animal life.
Many communities are thinking and acting long-term and using geothermally-heated sidewalks and roadways, these include Mammoth Lakes on the eastern slope of the Sierra Nevada and Brigham Young University in Provo UT. Although Mammoth Lakes' sidewalk and roadway system is in place, it is not yet connected to the geothermal heat source. This approach makes excellent sense. No need to plow and store snow, elimination of the need for sand and cinders, no problems with salt corrosion, works year round and the heat is renewable and stored in the earth.
Wow, you went one step further! I forgot about geothermal heat lol. Wonder if that's in place in Iceland...
Although it would probably be impractical to heat entire highways, it sure does make sense to use geothermal heat sources to heat walkways, parking decks and ramps, and overpasses. Some places already use heated parking ramps to eliminate icing of parking garage doors in winter. These systems are usually a gas boiler though. A primary advantage of heating the upper surface of the slab would be to eliminate the thermal effects from seasonal temperature changes. Especially in a climate that can range from -40 C in winter to +35 C in summer. A primary disadvantage is still cost. To run the PEX in the slab is costly, plus the installation of the ground-source heat exchange loops. Long term, there are enormous savings and everybody benefits in the end. With all that geothermal energy, I'd be very surprised if Iceland didn't use the heat for walkways. They already use the hot springs to heat homes. Salt has a lot of negative points when applied to roads. Ever notice how rusty cars are in Ontario, Minnesota, Michigan, Illinois, and NY state?
