Taking another "pass" at camp roads: building principles

Camping Magazine, July-August, 2007 by Rick Stryker

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 products that have really come of age in the past four years.

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.