Special Report: Lab Technology — How to Build an HMA Lab

Liberally borrowing from Tony Stewart's sponsor — You can do it. This article can help.

No, I'm not going to load up this article with a lot of NASCAR references in hopes that you'll keep reading. I'm hoping that if you've made it this far, you'll stick with me until the end. Some of what you read may be old news, but maybe you'll find a few nuggets that will help.

First things first

It sounds simple, but you need to know what kind of lab you're trying to build before you get started. Do you need a lab that is just capable of doing routine quality control work or do you want a design lab that can develop mix designs and evaluate mixtures for warranty work? The equipment will be similar between the two types of labs, but the design lab might have more and different types of equipment.

Regardless of the type of lab, there is some common equipment that any lab needs. For example, you'll need a variety of putty knives, spoons, scoops and gloves for handling asphalt mixtures. Paint cans and lids — quart and gallon — can be used for collecting samples of the liquid asphalt binder for testing (quart) or storing mix and aggregate samples for future testing (gallon). Baking pans of various sizes (such as 11" x 17") can be used for drying aggregates or heating/conditioning an asphalt mixture sample. A hot plate or propane torch is good for heating tools prior to use. Cleaning rags, solvent (such as mineral spirits), butcher paper, WD-40 – you'll figure out the miscellaneous stuff as you get into it.

Two other common items that need a bit of attention are scales and ovens. At the least you'll need a good scale capable of handling up to 10 to 12 kilograms with a precision of 0.1 grams. You'll need this level of precision if you're doing any mix testing to determine volumetric (air voids) properties. Unless all your testing is component analysis testing (determining asphalt content and gradation), then you'll also need a water bath with a heater and small pump/circulator like you'd find in an aquarium.

In virtually any lab, even a brand new one, it is an accepted fact that you never seem to have enough storage space or enough ovens. I'd recommend springing for at least two ovens up front. Forced draft ovens capable of up to 400 degrees F with a precision of 5 degrees F should be sufficient. This will allow you the flexibility of having one oven set for drying (230 degrees F) with the other set for heating asphalt mixtures.

Basic HMA testing

In years past, basic mixture testing simply meant determining the asphalt content and gradation of the asphalt mixture to ensure compliance with the specifications. This was as simple as performing a solvent extraction to determine asphalt content and performing a sieve analysis to determine gradation. Now, basic mix testing includes not only asphalt content and gradation testing (termed "component analysis") but also testing to determine the percentage of air voids and voids in the mineral aggregate, or VMA. This testing is often called "volumetric analysis."

To perform volumetric analysis on an asphalt mixture sample, you'll need two main pieces of equipment: a compaction device and a vacuum pycnometer (for determining the maximum theoretical specific gravity of an asphalt mixture sample). The lab compaction equipment of choice for most labs in the United States is now the Superpave gyratory compactor (SGC). There are several types and manufacturers of SGCs. The choice of which SGC to purchase comes down to a number of factors including price, user friendliness, and portability. Many labs have elected to use the smaller, more portable SGCs such as the Pine G1, Brovold, and Troxler 4141.

In addition to the SGC and a few molds, I'd advise purchasing a mechanical mixture simulation device for calibration of the angle of gyration. Of all the factors influencing the compaction of an asphalt mixture specimen in an SGC, the angle of gyration is, without a doubt, the most important. At low angles of gyration — such as the 1.25-degrees specified from the research — very small changes in the angle can significantly affect the density of the compacted specimen.