Winter gravel for ice

People ask for “winter gravel” when the real choice is between a deicer and an abrasive. A deicer makes brine and lowers the temperature at which that brine freezes. An abrasive sits between the tire and the ice and does nothing chemical. The Wisconsin Transportation Bulletin No. 6, Using Salt and Sand for Winter Road Maintenance, is a road-agency bulletin. Its rates are for trucks on roads. The size and the gravel-road warning travel better to a driveway than the pounds per mile do.

Salt melts. Grit grips.

The bulletin says rock salt, sodium chloride, has to dissolve before it can work, using moisture from the road. A 23.3 percent brine stays liquid down to −6°F. As the melt dilutes the brine, a 10 percent solution can stop melting and refreeze around 20°F. The same bulletin’s figure shows one pound of salt melting about five times as much ice at 30°F as at 20°F. Heat still has to come from the air, the sun, or the pavement. The chemical only moves the freezing point.

Plowing is the bulletin’s first way to clear snow. Salt is for the bond between ice and a paved surface. On gravel, the bulletin is direct: abrasives are normally used because chemicals soften the surface and plows scrape the gravel off. Low-volume roads in that bulletin commonly get abrasives only. A home gravel driveway is closer to that case than to a salted highway. Sand, slag, cinders, and bottom ash are the abrasives it names. Sand is the common one.

The size that belongs on ice

Dirt and very fine particles are not a cheaper grit. The bulletin says they hurt traction. A washed, angular sand is the description that matches the note. The pea gravel calculator is for the rounded stone, which the driveway section of that page already keeps off a surface that has to carry cars. The #57 calculator is for No. 57, nominally about 1/2 to 1 inch. Broadcasting it on ice fights the 3/8 inch line and wastes a drain stone.

Application, and the rate not to copy

Abrasives work only while they stay between the tire and the ice. The bulletin says they are usually applied at curves, intersections, railroad crossings, and hills, at 500 pounds (0.18 cubic yard) to 2 cubic yards per mile, and that heavy traffic or a later snow buries them so the pass has to be repeated. It also says a spreader has to be calibrated because the same dial does not throw every material at the same rate. Those sentences describe a maintenance truck. Dividing 0.18 cubic yard by the 5,280 feet in a mile and multiplying by a 40 foot driveway would pretend a house apron is a shaded curve on a highway. This page does not do that division.

If you are buying a pile of traction sand before the season, the pile has a volume. The sand calculator starts at 1,600 kg/m³, the same clean-material default as #57, about 1.35 short tons per cubic yard. A quarry ticket that prints a different density belongs in the density box. Weight of a yard you already know is the tons to yards calculator. Neither page knows that the sand is for ice.

Blending salt into the sand is a separate argument in the bulletin, and it is mostly a warning. Salt at 50 to 100 pounds per cubic yard is described as a way to keep a stockpile from freezing. Adding more, so the blend is supposed to melt and grip at once, works against itself: the melt shoves the grit into slush, or the plow throws both away, and the salt melts less ice when it is diluted by sand. The bulletin’s advice is to use straight salt when salt is the right tool and a freeze-proofed abrasive when it is not. On gravel, salt is the tool that softens the surface. Skip the blend.

Cleanup

Salt leaves in the meltwater. Sand stays. The bulletin says the particles clog inlets and sewers, and that cleanup may be necessary in town, on bridge decks, and in ditches, because the grit washes into streams. It also notes concern about the fine dust, the particles under 10 microns. None of that is a price, and none of it is a date on the calendar. It is the reason the spring pass on a gravel drive should not treat leftover ice sand as driveway stone. Sweep it off the wheel paths before you reshape the surface. The spring driveway page is the reshape and the new stone. This page stops at the grit.

Where you stage the pile matters as much as the particle size. The bulletin’s cleanup section is about sand that washes into inlets, ditches, and streams. A pile stored on the uphill side of a storm drain, or spread in a thick blanket over the whole drive “just in case,” is the same material, one rain away from that ditch. Put down enough to cover the ice under the tires, at the slope and the bend, and leave the rest in the pile. The bulletin also says abrasives scatter off a road once speeds are high, which is why a highway pass is short-lived. A driveway is slow, so the grit stays longer, and it is still there in the spring unless someone picks it up. That is a reason to use less, not a reason to switch to pea gravel because the pebbles look neat.

A paved walk is the case where salt can be the right tool and grit is optional. The bulletin is written for pavements that are supposed to go back to bare surface, and for gravel roads that should not be salted. A concrete step can take a deicer chosen for concrete. A gravel drive should not borrow that habit. This site does not sell either product and does not print a price per bag or per ton. If a neighbor’s method is a salt-and-sand blend from a highway shed, that blend is the practice the bulletin says wastes both materials, and on gravel it is the practice that softens the surface.

Sources

• Wisconsin Transportation Bulletin No. 6, Using Salt and Sand for Winter Road Maintenance. Salt versus abrasives, the gravel-road warning, angular particles under 3/8 inch, road application rates per mile, and cleanup of sand in drains and ditches.

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