 It's an important job we do in the aggregate asphalt and concrete manufacturing industries. After all, we're more or less responsible for creating the roadways that literally keep this country moving. The process all begins right here, rather modestly with aggregate. By mixing fine and coarse aggregate with Portland or asphalt cement, we're able to manufacture a quality product that's durable and serves us well. But in recent years, the process of stockpiling and loading aggregate has become more critical. Quality conscious customers have begun to sample asphalt and concrete on a more frequent basis, with the goal of assuring the products they buy are a proper blend of aggregates. They know that for a product to hold up under today's increased traffic loads, it must be constructed correctly. If it's not, well, the product may fail. To an aggregate manufacturer, this often means a customer returns a shipment but refuses payment, or accepts a shipment that pays only a portion of the asking price. As you can imagine, a company that must make these concessions might not be in business for long. So the question is, how do we avoid supplying substandard aggregate? Well, to answer that question, we have to take a look at where the problem frequently begins, and that takes us right back to our aggregate stockpile. This stockpile model clearly shows how material will segregate. As an aggregate stockpile is built, large particles tend to separate from smaller particles. It's simply a matter of gravity. We've come to know this process as segregation, and no matter how a stockpile is constructed, the possibility of segregation must be considered. For instance, if you take a close look at a stockpile that is built from a fixed conveyor, you'll notice that fine materials tend to sink to the bottom as it moves along the conveyor belt. As a result, the fine material drops directly down the conveyor to the inside of a stockpile. Larger material, on the other hand, is projected away from the conveyor to the outside of a stockpile. The result? Segregation. A stockpile that is created from a radial stacker has similar segregation. Even though the conveyor moves, creating a more tent-shaped stockpile, fines tend to fall to the inside while larger particles fall to the outside and away from the stacker. A stockpile built from end dumping often exhibits even more dramatic results. During transportation, fines again tend to settle to the bottom of the truck bed, so when the truck dumps its load, the fines fall directly down the dump wall to the inside of the stockpile. Coarse material, once again, gravitates to the outside. Truck-built stockpiles, made by dumping truck loads of aggregate adjacent to each other, also are segregated. The problem of segregation really comes to light as a front-end operator begins to load a truck or bin. Now, imagine what happens if an operator takes his load from only one point within a pile. For a product like Asphalt or Concrete, whose formula relies on a cross-section of aggregate to assure strength and durability, well, we've just greatly compromised that formula. So that's the bad news. No matter how a stockpile is created, it has a tendency to segregate, and as a result, an operator can easily load a poor mixture of aggregate. But there is some good news. Segregation can be overcome with a relatively easy loading procedure. Knowing that fine material just naturally separates from coarse material in a stockpile, a loader simply needs to make sure that he loads from all portions of the pile, and as a result, blends an even mixture of fine and coarse material. This procedure can best be accomplished by repeatedly taking bucket loads from across the entire face of a pile. The rule of thumb here is to visually divide the pile into thirds. Start loading at one end, let's say the left third, move to the center, then move to the right third of a stockpile. You'll want to repeat this procedure until your load is complete. This rule of thumb should be followed for a cone-shaped pile built by a stationary conveyor, a tent-shaped stockpile formed by a moving conveyor, and an end-dump stockpile. An operator should also make sure he enters the stockpile as low as possible without scraping base material, and then raise the bucket up through the pile. This simple movement is especially important in a multi-layered truck-built stockpile because it helps to assure an operator is getting as thorough a blend as possible. Now there are a couple of other procedures you'll want to keep in mind to help minimize segregation. First, don't hesitate to reposition a truck that may be blocking your access to the entire face of a stockpile. In the long run, the few minutes it takes to explain to a driver why he must move may eliminate an unhappy customer, or that same driver returning a highly segregated load. Second, be sure that as you load a truck or bin, you don't segregate a properly mixed load of aggregate. For a standard tandem dump truck, that means gently rolling the aggregate into the truck bed, rather than dropping it from an unnecessary height. When loading an 18-wheeler or a belly dump, load the aggregate in three steps across the bed of the truck. The first bucket in the front, the second in the back, and then in the middle. You should repeat this front, back, middle procedure until the truck is full. Also, remember to just roll the load from the bucket. Again, this helps to further minimize segregation. So there you have it, some very simple procedures that will help minimize the very serious problem of segregation. After all, it's an important job we do in the aggregate asphalt and concrete manufacturing industry. By minimizing segregation, we not only help assure that our businesses remain profitable, but that the roadways we build will be around for the long haul.