Every time I visit the Montana Legislature website, I’m amazed at the range of legislation (from insane to brilliant) up for consideration. Thank goodness most of it dies a well-deserved death. However, one bill near and dear to my black little heart is sponsored by Sen. Dee Brown (R-Columbia Falls): Senate Bill 117, to Revise Highway De-Icer Laws.
SB-117 would, if it passes, reduce over time the use of what many of my pro-driver friends bitterly call road slime – “liquid de-icers containing sodium chloride or magnesium chloride.” Brown’s bill would mandate that the use of either chloride “must be reduced from the current level of use by 10 percent each year over the 10 years following” the bill becoming law, or until use drops to the average used yearly from 2007 to 2010. Rock salt mixed 1:10 with sand would not be affected.
The bill passed second reading in the state Senate on Feb. 1, three days after it passed the Highways and Transportation Committee, and was then “rereferred” to the Finance and Claims Committee for a Valentine’s Day hearing and later vote.
Gosh, I hope it passes. Words (at least family-safe words) can’t begin to describe how much I have grown to hate magnesium chloride.
Highway departments, however, seem to love mag chloride. One, it controls dust on gravel roads pretty well. Two, it melts road ice down to near 5 degrees Fahrenheit, 10 degrees better than plain old salt, making our highways “safer.” Three, I guess it’s “cheap.”
But the very thing that makes mag chloride work so well on gravel roads (cutting the “loss rate” of good stuff by up to 60 percent) and at fighting ice in winter, makes its use a terrible devil’s bargain.
First and foremost, mag chloride (like plain salt) is “hygroscopic.” Alongside salt, magnesium chloride sticks to water and never lets go – that’s why oceans are salty. But we’re not talking just “wet water.” Salt, and to a greater degree, mag chloride, both actively suck moisture from the air.
That’s how mag chloride works on graveled roads – it grabs air moisture (especially at night when humidity rises) and retains it in the road structure, the effect being the same as regular rains or passes with a water truck, keeping the road dirt “damp” and cohesive.
In winter, mag chloride works for the same reason. It grabs, and keeps on grabbing water, whether wet or from vapor. Any water that attaches to it stays liquid, all the way down to five degrees. Awesome, right?
Um, no. Have you ever noticed how the guck on your car never dries out or seems to freeze unless it’s screaming cold, way too cold to wash your darn car? And have you ever noticed how water seems to always find a way to where it’s not wanted? Through the tiniest little crack? What do you suppose is going on in places you can’t see?
Yep, because second, we’ve all seen what “sea breezes” do to all kinds of metal. Salt mist is terribly corrosive. Mag chloride mist? Even more so. A salt crust will at least dry out when humidity is below 70 percent, but not mag chloride. It is so hygroscopic that it will keep sucking moisture from the air, even in deep cold, staying chemically moist and therefore continuously corroding everything it touches, especially in places you can’t scrub. How do we know this? When important parts either rust shut, fall off, or the lights stop working.
That’s not all. Mag chloride also likes to eat concrete. It carries into the pores of concrete when wet (don’t forget, this stuff keeps working down to 5 degrees Fahrenheit, not 32 degrees). Inside the wetted concrete, the magnesium reacts with two of the three main concrete chemicals – basically turning it into “not concrete.” Where does that show first? In cratered bridge surfaces like the 40 bridge over the Whitefish River and West Reserve over the Stillwater.
Even better, gravity, time and a low freeze point helps this mag chloride soup soak through the concrete into the subgrade, then into the water table. Or, in the case of bridges, into the contact points where the steel support structure meets the bridge deck – not just the girders we can see, but the stressed rebar we can’t.
There’s the animals killed, attracted by either “salt,” and cars damaged. There’s the old saw about salting the fields of the enemy, in this case our roadsides and beyond. And while I can’t prove it yet, I’m convinced that slime kills the reflectivity of road paint, making night driving much more dangerous.
Gosh, stop sliming us, please.