Friday, June 22, 2012

The Folly of Brick Sidewalks


Every town in the US with a historic area, whether real or recreated, likes to replace their plain Jane concrete sidewalks with brick. It’s an expensive undertaking that’s also tough to maintain. Just think of all the times you’ve seen a missing brick in one of these walkways. 

Simple concrete slabs rarely disappear, though they may crack thanks to vandalizing tree roots or dimwitted contractors. Trees in urban areas are often planted in spaces too small for the root ball. A healthy tree will ultimately remedy the problem and bore underneath the paving, then slowly expand and lift everything above it. Bricks are easier to lift than slabs of concrete, but both will ultimately give way. 

It is true that brick has an advantage when it comes to trees, though. It can be a permeable surface that allows water to reach the roots. In the Netherlands, brick is used in both walkways and streets to allow the constant rainfall--- think Seattle, only with more wooden shoes--- to soak in rather than drain off. The appeal of this is obvious: much of the Netherlands is built on reclaimed land that’s below sea level. All that runoff has to be pumped up and into one of the many canals that are, in turn, pumped into the diked rivers. It’s much easier to just let a lot of it percolate into the soil. Their bricks are set in a sandy base that’s tamped down with what looks like a jackhammer that someone forgot to remove the protective cap from. Once the sand is thoroughly packed, a team of workers moves in to carefully place the bricks flush against each other, all the while cutting the bricks with what must be the world’s strongest powersaw blade so that there are no gaps at all. It’s a labor-intensive task that you won’t see too often in areas governed by cost-conscious (a polite way of saying cheap) politicians. 

Our version of brick sidewalks tends to be a choice between “good-enough” and “cheating”. The “good-enough” model is that the bricks are set haphazardly on soil (not necessarily sand) that’s been vaguely smoothed over. The undulating surface will worsen over time as seeping water erodes the uneven subsurface.
The “cheating” method involves setting the bricks in concrete. Any gaps are filled with concrete, so little brick-cutting is involved. Unfortunately, concrete tends to crack and crumble as the bricks expand and contract with the changes in the weather. That means the bricks will start to loosen and, inevitably, pop loose.
For someone with trouble walking or with vision impairments, loose or missing bricks can be a tripping hazard. If that person is elderly, a sudden fall is potentially dangerous. An undulating surface can be just as hazardous, as a brick’s edge might pop up just enough to trip someone. 

A brick sidewalk in Old Town Alexandria. Notice how it undulates towards the top of the picture. This one is actually in decent condition. Photo by author.
That permeability that’s so advantageous in the Netherlands can backfire spectacularly in the US. Some cities made the mistake of burying the bases of traffic signal poles underneath their brick sidewalks. Sure, it looked a lot better to have those unsightly metal bolts out of sight, but the water percolating through the brick rusted those same bolts. That’s why some cities such as Alexandria in Virginia are taking the wise precaution of replacing old, partly buried signal poles with new ones. Collapsing traffic lights are upsetting to both tourists and voters. 

The new traffic signals being installed in Old Town Alexandria, VA. The old signal is on the right. Note that its base is buried under the bricks, which trap moisture and rust the metal. The new signal on the left has an exposed base. Photo by author.
So given these problems, why are brick walkways so popular? Blame it on skewed priorities when it comes to preserving our historical sites. In the early 20th century, Colonial Williamsburg was rebuilt from ruins while colonial dwellings in Old Town Alexandria were rigorously preserved through the creation of one of the first historic districts. New urbanism developments such as Kentlands in Maryland emulated the colonial motif, right down to the brick walkways. By contrast, Native American burial mounds such as the Ocmulgee Old Fields in Georgia that are thousands of years older remain under threat of highway construction. The prevailing culture in the United States prizes the colonial aesthetic above all else.

So is there an alternative to dangerous, ill-constructed brick? Happily there is: stamped concrete. This surface is smoother than brick thanks to its inherent uniformity with as little as a 15% cost premium over regular, bland concrete. It spreads out like a regular slab, only with a stamping process to create a pattern. This pattern can mimic brick, if that’s what floats your colonial boat, right down to the color. That’s really the cool part: the concrete’s color doesn’t come from paint, but from a sort of dye that’s added into the mix prior to pouring. That means the color doesn’t flake off.

This stamped concrete is over 10 years old and shows no sign of cracking. It's located in front of the Courtyard Inn Center City in downtown Philadelphia, PA. It must endure a harsh freeze/thaw cycle and heavy vehicular traffic. Photo by author.
Yes, there are some negatives. As with any material, stamped concrete can crack if not poured properly. It’s always amazing to me how few contractors understand that expansion joints have to be put in between slabs. A single giant slab is doomed to crumble. 

Another drawback is public perception. Some preservation purists will insist on using real brick because it’s what the colonists used. Never mind that those lovely brick sidewalks and streets were either unpaved or lined with planks in the actual colonial era. It’s the perception, however erroneous, that counts with these folks. 

The bottom line is that any municipality of developer that wants to improve the ambiance of a given area should think twice about using brick as anything other than the façade of a building. As a paving material, it is costly and labor-intensive. Stamped concrete can look just as good, be safer to use, and last longer. Just be ready for some griping from a few purists.

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