Winter’s toll on the Roads

Winter is a tough season on anything exposed to the elements. Plants die. Animals hibernate. Waterways get caught in a messy game of freeze and thaw.

But our roads also bear winter’s brunt.

And it’s not snow and ice that are the biggest problem—it’s what we do to remove them.

Winter moisture alone already does a number on concrete by itself, as water—snow melt, sleet, runoff—expands 9 percent its original size when frozen. That means when concrete freezes, any moisture in the concrete can create pressure in the pores of the concrete. When this pressure exceeds the concrete’s tensile capacity, it causes cracking and spalling of the concrete surface.

If large aggregate in the concrete is porous or absorptive, the moisture in the aggregate can freeze and crack and split. If these aggregates are close to the surface, they can create pop outs that look like cone shaped indentions on the surface of the concrete. This cracking can also create D-cracking, which is closely spaced cracks that parallel joints. These cracks will continue to multiply over time and show up further and further from the joint.

Deicing chemicals can make this process worse in different ways.

First, the deicing chemicals reduce the freezing temperature of the offending moisture. So rather than the moisture in the concrete freezing at 32 degrees and staying frozen until the concrete temperature exceeds 32 degrees, it thaws at a lower temperature and refreezes at a lower temperature. Therefore, the concrete goes thru more freeze/thaw cycles than it would have if deicing chemicals were not used. Each time the concrete freezes, it repeats the expansion pressure that can create more cracking and spalling.

Most deicing chemicals contain chlorides. These chlorides are like sponges that attract and hold moisture. Therefore, concrete that is more saturated with chlorides is probably more saturated with moisture and thus more susceptible to damage when the concrete freezes.

Even worse, certain deicing chemicals can actually chemically attack concrete. Deicers containing ammonium nitrate and ammonium sulfate aggressively attack and disintegrate concrete.

But that’s not where the wear and tear stops. The same chlorides that weaken concrete also bombard metal with enough moisture that it will rust—a huge problem when you’re talking about concrete reinforced with metal. When metal rusts, the rust can become four times larger than the original metal, causing the concrete it is reinforcing to expand and crack. And once this process starts, both the concrete and the steel deteriorate even faster than before.

There are various ways to protect concrete and steel from winter’s ways—air entrainment, low permeability in concrete, etc.—but the best thing for our roads can hope for in the winter? No moisture.

Let it snow? Not if you’re a road.