How to Determine Fluff Factor and Yield
Here’s How to Determine Fluff Factor and Yield
In earlier modules, you learned how to measure and set auger height correctly. In this module, you’ll learn exactly why that step is so important. When placing the mat, you have to accommodate the amount of mix to be compacted during rolling. Think about it: the mat you place will be more compact after you roll it. That’s the point!
To achieve the correct mat thickness after compaction, you will place the lift a bit “taller” than the final spec requires. In other words, if the mat is supposed to be one inch thick, you will place a lift of one and a quarter inches. That extra quarter of an inch is known as the fluff factor. The foreman is typically the member of the crew who calculates the fluff factor, which is the mat thickness that the screed will place, by adding one quarter of an inch to each inch of final thickness the project calls for.
You will use the automation on the screed to dial in the height of the mat you place, but it’s vital to double-check your work.
Take your level to the back of the screed and lay it transversely across the joint, like you see here. Use a wooden folding ruler to measure the distance between the base of the level and the existing mat, which is the one you’re matching.
That measurement is your fluff factor.
That measurement must reflect the exact amount you’ve built in for compaction.
Now let’s talk about calculating yield. Determining how far a load of asphalt mix will go takes a quick bit of math, but it’s vital to making sure you don’t run over on the job. The yield is the amount of material being used in a set area. It’s important to know so you can keep track of where you are during paving, how much material you have at any point in time, and how much material you may be wasting or running low on. There are online calculators to help you, or you can use the equation provided at the end of this lesson to figure the yield.
There are three constants to know to calculate your yield. Paving width. Paving depth. Tons of material.
When you know the values for the three constants, you plug those values into a calculator to determine what distance the paver should travel.
If you have a distance calculated, but the paver doesn’t get that far with its load, you will know there’s a problem. That might mean that your depth is set too high, there’s a dip in the subgrade, or some other such problem. You’ll know that something needs to be double-checked and fixed.
Or, if you have a distance calculated, but the paver goes past that mark with its load, you will know that you’re paving too thin. Again, the depth may be set too low, or there may be a rise in the subgrade.
You might think this problem is a better one to have than running out of mix, but consider the rolling train that’s trying to get compaction on a thinner lift than planned. The roller operator set his vibration and impact spacings based on the mix and lift thickness. Also, if you have a state spec to meet, it’s vital to correct what’s going wrong.
To calculate yield, you will divide the number of tons of material by the depth to be paved. This will tell you the square yards that amount of material will pave. Take that number—the square yards—and multiply it by 9 to get the square footage and divide that by the paving width to learn the linear feet the material should pave. For example, if you are paving 10 feet wide and 1 inch deep, a truck delivering 18 tons will let you pave 285 linear feet. Check out the math on the screen to see this.