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Building Principles: Taking Another "Pass" at Camp Roads
Several years ago (March/April 2003), Building Principles took a broad look at camp roads. Recently, we've had a number of calls about road issues so we thought that this might be the perfect time to expand on the roadway topic a bit, and talk about a few
Bituminous concrete ("asphalt" or "blacktop"), known as "flexible pavement" in the industry, is probably the most common roadway surface you'll find, not just at camp, but everywhere. That's true for a host of reasons but mostly because it's relatively inexpensive (though prices have skyrocketed with the increase in petroleum costs) to buy and install. Some people even think that it's cheap and easy to repair, and when it's done badly, they will correct it . . . at least for a short while. Let's look at why asphalt fails, and then it will be clearer why a properly done repair may not be as inexpensive as we thought.
We all have experienced the "flexible" part of "flexible pavement" at the height of summer, when the parking lot feels soft under our feet. The opposite effect happens in the winter: asphalt roadways get very hard and brittle when cold, and being exposed to the weather it's the first layer to freeze and the first to warm. If the asphalt and the layers beneath are frozen, the stacks of material act together to support any loads applied. When the road bed is frozen, but the asphalt is soft (like on a south facing hill during a sunny day in January), the layers can separate ("delaminate") and allow seepage through surface cracks. When the water freezes again, it expands and makes the condition worse. Sheets of road surface lift, are stripped by the snow plow, and deposited on the shoulder or ditch. Large, relatively shallow potholes usually result from this particular cycle. Also, heavy loads on pavement can add to and accelerate the deterioration (e.g., a plow truck full of cinders or salt). Finally, what about in the spring, when both the pavement and the road bed below are above freezing, but the bed is saturated with snow melt and ground water? Vehicles traveling over the "raft" of asphalt have little to no support beneath, the asphalt yields, and deep potholes develop.
This path to failure is no secret to the folks who design, build, and maintain roads all the time, so how did we come to this place? Think back to a time before the asphalt. Who remembers that the road was gravel or dirt and it was always full of potholes, ruts, and washes? Someone called the local paving company and told them to "blacktop the road." They did, and it looked great for a while. But now the potholes are more abrupt than they were in the gravel road, and the repairs are more expensive. No need for a show of hands, you know who you are. Take heart, though, because just about everyone else is in that boat too!
Road Construction 101
Because climate, conditions, and local practices vary widely, every state Department of Transportation (DoT) has developed a list of criteria ("specifications") for road building materials from the stone base through the asphalt layers. Learn what those designations are and what they represent so that you understand what the contractor is talking about. From the bottom to the top, the materials get gradually more fine with fewer and fewer spaces or voids between the particles. The last layer, just under the asphalt, will likely be a crushed stone and dust combination so that the voids between the individual stones are completely filled with stone dust.
Beginning with the native soil, each layer should be as tightly compacted as possible. When the lowest elevation for the road has been excavated, the native earth is compacted. Sandy soils are best compacted using vibration and knobby steel rollers (sheep's foot). Rubber-tired rollers are used for other soils and rely on their sheer mass to compress the material beneath. Back and forth, the equipment rolls and pounds the material until it is "tight enough." But how do you know? There are laboratory tests that can confirm the compaction, but these take much time and money. Instead a field test called a "proof roll" is conducted like this: Before a new layer (or lift) is added, a fully loaded dump truck of stone drives slowly down the compacted area with a checker walking behind watching the impression made by the wheels. Any location where the material appears to move under the load is marked with spray paint for rework. Sometimes it just needs more compaction. Other times, the area has to be dug out, replaced with new material, and then retested. Only when the entire run has been tested and passed "proof roll" is the next layer allowed to be placed. By ensuring that each successive layer is packed as tightly as possible, there is more and more certainty that the road will resist water intrusion from beneath. It should be more clear now why "blacktopping" that existing gravel road without compacting the material beneath is a sure recipe for pavement failure, sooner rather than later. This may seem time consuming, and perhaps it is. But it is a world cheaper than a failed roadway.
Through proper material selection and thorough compaction, we've worked really hard to make sure that water is excluded from our road base. We're ready for the asphalt. This too has specifications that your DoT has set up for your conditions, and the same homework is required to research the details. Too much bitumen ("black stuff") will make the mix too soft. Given the current cost, that won't probably be a problem, however not enough bitumen will make the pavement brittle. There simply won't be enough glue to hold the aggregate together in the proper matrix. In addition to mix recommendations, the regional office of the DoT will probably be glad to offer suggestions about how many inches of asphalt binder (bottom layer) and wearing course will serve your traffic load economically.
One other detail that shouldn't be overlooked is known as the "tack coat." This is a coating of raw bitumen emulsion that glues the layers together to prevent delamination and to help to exclude water infiltration from the surface. It's expensive because it's all petroleum product (with some sand), but it will pay for itself. Don't skip it.
Most roadways are constructed to direct water away from the centerline. That is, they slope toward both shoulders. This is called "crowning," and while it's more prevalent in the northern climes, it's not unheard of in the rest of the country. One-quarter of an inch per foot (2 percent) is pretty common, and normally it's built in to the placement of the asphalt by an adjustment in the machine that lays the coat of material down (called the "screed"). It's then compacted and shaped with a hot roller to set the final cross-slope or crown.
Making It All Go Away
We've now built a road for the ages. The Roman Empire would be proud. But what will happen to the rain and snow melt? We got it to the edge of the pavement with the crown, but where does it go from there? Where there is no curbing (who has curbs along camp roads?!?), the shoulder should be wide enough to accommodate vehicles, compacted to withstand wheel loads, and sloped steeper than the roadway. It's likely that the shoulder material will be rougher than the smooth pavement, so water will tend to slow here. For example, where the normal crown is 2 percent, shoulders are often sloped at 4 percent to shed the water into the ditch. There should be about a half inch of drop. More than that, and water will tend to channelize along the pavement edge and erode the soil. Less than that and the grass will tend to grow over the pavement and create a dam for the run off. The best way to go is with a gravel or crushed stone shoulder (properly compacted of course!) which has no drop off at all.
Who Can Afford That?!?
We're fond of telling folks that you can pick any two of the following for each project you undertake: You can have it right, fast, or cheap. When you're thinking about rehabilitating thousands of feet, sometimes miles of roadways, costs sure can add up in a hurry. Nobody that we work for can afford to peel up their roads and start over, so instead we recommend that roadway rehab be part of an annual improvement investment program. Commit to (and follow through with) budgeting a certain amount of money or a section of road each and every year, and rebuild it right. Start with the areas that are in the most distress or which represent the greatest risk to your guests, and do what you can this year. Next year, take on the next spot on the priority list. Before long your roads will have a somewhat patchwork look, but properly built and managed, you'll be in great shape to top off the whole thing for your final roadway construction installment.
As usual, an ounce of prevention is worth a pound of cure (thank you, Ben Franklin). Proper drainage of the road bed means that it is largely without water, and therefore not inclined to freeze and thaw as dramatically. Unfortunately, most, if not all, camps have roads that didn't receive enough attention and care when they were built in the first place, and now it's come home to haunt your organization today. Stop the madness! Spend the money well, and your investment will benefit your successors for years to come.
Rick Stryker is a professional engineer (P.E.) whose practice specializes in study, design, consultation, and permitting for facilities and infrastructure at camps and conferences nation- wide. He can be reached at 570-828-4004 or at firstname.lastname@example.org.
Originally published in the 2007 July/August issue of Camping Magazine.