February 24, 2013
Pennies DO matter in an aggregates operation.
In a recent conversation with Shane Buchanan, asphalt performance manager with Oldcastle Materials Group’s Asphalt Performance Team, about mix-design optimization, he told me how watching your pennies can save your operation millions.
But it’s not about cutting corners to save money. It’s about doing your homework and understanding calculations in mix design. He points out that when designing a mix, it’s important to conduct a quick review of mix volumetrics to make sure you know what you think you know.
“A lot of times when people are new to the industry, they are trained by someone else who was trained by someone else,” Buchanan says. Throughout time, training can get somewhat diluted. “People take leeway on concepts. If three steps removed from truth, you may not know exactly the correct way.”
This makes it important, he says, for a person to go back to the beginning and not just use the information on which he or she has been trained by another person or through internal training.
“You can really get into trouble by not understanding volumetrics,” Buchanan explains. “You need to understand impact of aggregate grading on volumetrics, of asphalt grading on volumetrics. The most critical volumetric property is VMA [Voids in the Mineral Aggregate]. VMA is one of those targets that is sometimes very difficult to achieve. How do you achieve it? That is the million dollar question. The whole question dovetails into other concepts.”
Before trying to just achieve volumetrics, Buchanan says, you need to understand what it means. “Do not get caught in the trap of using formulas blindly,” he points out. “At least go back and work a volumetric phase diagram from start to finish so you can understand what all the components mean when tackling volumetrics. It is all related to mass and volume, so there is just one way to do it correctly.”
This information is easily found online, in a National Center for Asphalt Technology (NCAT) textbook, through the National Asphalt Pavement Association (NAPA), or even a state asphalt association, Buchanan says.
“Never be too proud to review the basics,” he says. “Pride has cost a lot of companies a lot of money. These days, that’s the last thing you can afford. Very likely, it is costing you a lot of money.”
When you design the mix, Buchanan says, you need the minimum VMA — but you don’t need too much. It can be equated to the extent of the mix. One of these components is your liquid asphalt content.
Typically, during production, you will lose VMA, Buchanan says. If you are designing with a VMA of 14.5, typically, you are going to 1/2 to 7/10 of VMA during production. This is referred to as “VMA collapse” and is due to excess volume.
“Knowing that you can design your mixes with that cushion, if minimum VMA is 14, you may choose to design 14.5 to 14.7 based on your history or experience,” Buchanan notes. “Some states will pay on VMA during production, some will not. That also goes into the equation on the mix design side. If you’re not specifically paid on VMA during production, it will drive you in a different direction.”
This means paying attention to your aggregate gravities. Make sure you gravities are very accurate.
Typically, coarse aggregates make it easier to get the correct gravity, Buchanan says. “With fine aggregate, you can have the issue of getting the correct GSP determined. That is the cause of the test method.”
The test method is such that materials with a lot of fines, such as -200, can give a misleading result. This can cause you to undershoot your bulk gravity, and have bulk gravity and absorption that is too high. Relating that back to VMA, a critical factor in VMA is bulk gravity of aggregate blend.
“The takeaway is that if you are getting incorrect bulk gravity — if the gravity is too low — the result will be a slightly lower VMA calculated, and you are directly penalizing yourself,” Buchanan says. “A 100th change in your bulk gravity is a 3/10 change in your VMA.”
With regard to aggregate gravities, if you are calculating gravities, Buchanan says, “you should pay very close attention to aggregate absorption. If at all possible, use the absolute lowest absorption possible. The higher the absorption, the more liquid asphalt will be absorbed in the stone, so you are just wasting money. A good rule of thumb is that asphalt absorption will be about 50 percent of water absorption.”
Buchanan gave an example from his own company. He says Oldcastle realizes that liquid asphalt price drives the mix cost, so anything you can do to optimize your mix with regard to the amount of virgin liquid in the mix is going to go directly to your ability to make money.
“You assume that your virgin liquid is about $550 per ton,” he says. “That means every 1/10 of liquid you can save has an impact of 55 cents per mix ton. That is a lot money.”
Oldcastle did 44 million tons, plus, Buchanan told me. If you take the factoid we just discussed, that is a potential savings of $23 million.
“In an industry that is driven by volume, this is essential ,” Buchanan says. “Just saving s few cents per ton makes a difference! The savings, incrementally, are small. Once you hit the volume escalator, it is a tremendous savings. Pennies Matter! You can’t fall victim to thinking pennies don’t matter.”
Buchanan finished our conversation with a quote from Paul Getty: “’If you look after the pennies, the dollars will look after themselves.’ That is the philosophy every [operation] should take.”
Look for future posts about mix-design optimization from my conversation with Shane Buchanan. He had fantastic insight. I look forward to sharing more with you!
Shane Buchanan will also be giving a presentation at the World of Asphalt/Agg1 on “Mix-Design Optimization.”