By Tony Wight
Many of us know there are a multitude of problems and issues that need to be avoided when paving either a road, commercial parking lot or a driveway. Everything from water flow and slope to texture and shadows in the mat. One of the major challenges is putting down a product that will hold up over time. This requires starting off with a solid base but it needs many things to go well all the way to the top coat.
One downfall of many jobs is segregation. Segregation is when the large stones in our mix roll or separate from the fines. This can sometimes be seen as a spot where there are voids between large stones. (No fines between the larger stones.) This can allow water to get into and under the layers of asphalt and this can cause a failure in the finished product.
Segregation will show up in several forms, Truck End Segregation (one or both sides), Center Line Segregation, Joint or Edge Segregation and Random Segregation. Segregation can start anywhere from the way the plant builds its stock pile to how fast or slow you run the augers. Remember anytime you move or convey material segregation can occur.
Truck end segregation takes two forms. First, one-sided is normally caused by improper loading of the batcher at the plant but can happen in loading the truck as well. Two-sided truck end segregation is most often caused from improper loading of the truck when dumped from the silo. Remember to take three drops in a tri-axle and two drops from a tandem axle truck. Truck end segregation can also occur when dumping a new truck into the paver. Try to remember to leave some material in the hopper when engaging a new truck. Less surging of material into the hopper will help stop segregation.
Centerline Segregation normally occurs in the paver. Some pavers have a center auger drive box that blocks the material from falling directly down in the center of the screed causing a build-up of larger aggregate. This is corrected by putting a small section of augers mounted backwards to wash the material through. This can also occur if the screed extensions are brought in and out several times in a short amount of time.
Joint or Edge Segregation occurs at the end or edge of the mat, or at the joint if you are matching joints. This is normally caused by running the augers and conveyors too fast or paving faster than the conveying system can keep up with. This can be fixed by running your conveyors slower and not bringing in your hopper wings as much. The next thing that will help is augering shorter distances and running your augers as slow as you can while still keeping up with paving speed. Remember your best and most efficient paving is 11 to 13 foot wide.
Random Segregation is one of the hardest to determine where the problem is coming from. Most times it is somewhere at the plant. Most often in the drum or silo. Remember it can start at the aggregate stock pile. Take a drive past one of the asphalt plants aggregate stock piles and you will see segregation at the bottom edge of all the piles. Most plants correct plant issues by how they draw from the stock pile when loading the stone into the plant. Then they also add baffles at places in the mixer, batcher and silo to help keep segregation from occurring.
Practice good paving principals. Load the truck properly and pave 11 to 13 foot wide. Run your conveying system at a slow steady pace and pave at a speed that allows everything to flow smoothly. This makes for a better job which can show by meeting ride specification and density requirements or having a good looking parking lot. All of this will help you make bonus money on a highway job or keep an owner happy.
It’s a great day to pave.
Tony Wight, LeeBoy Territory Manager and can be contacted at twight@leeboy.com
