Testing, Testing

Are we testing the right things?

By Juan D. Hermosillo, Ph.D. Martin Asphalt Company Major Associate Member Chair

If you’ve ever tried to check the temperature of a steak with a thermometer, you know there’s a right way and a wrong way to do it. Stick the probe into the thickest part of the cut and you get a reliable reading. Hit a pocket of fat or get too close to the surface and suddenly that same thermometer is telling you a completely different story.

The thermometer didn’t fail. The measurement did. Asphalt binder testing works the same way. In Texas, asphalt binder is tested multiple times before it ever becomes part of a pavement. There are supplier quality control testing, verification testing, and quarterly sample and field sample testing by TxDOT, each serving an important role in ensuring materials meet TxDOT specifications. On paper, this layered approach provides confidence that the material being produced, shipped, and ulimately placed will perform as intended.

And in many cases, it does exactly that. But there is an important question worth asking: When results don’t line up between tests, are we seeing a true difference in the material, or are we simply testing different samples? Because at the end of the day, every test result is only as good as the sample that went into it.

Asphalt binder is not a perfectly uniform material sitting quietly in a tank. It is influenced by temperature gradients, storage conditions, blending practices, and movement within the system. Even in well-managed terminals, there can be subtle variations within a tank, a transport vessel, or a distributor. Those variations are usually small, but they become significant when the goal is to measure properties with precision.

Now consider what happens when samples are collected at different points in the process. A sample pulled from a terminal tank may not perfectly represent what is loaded into a truck. A sample taken from a distributor may not reflect what was originally produced. A field sample collected after transport and handling may have experienced temperature changes, contamination risks, or segregation effects. Each sample is valid in isolation, but they may not be identical representations of the same material.

That is where the challenge begins. Multiple layers of testing provide redundancy and accountability. Supplier quality control testing ensures material leaving the terminal meets specification. Independent or agency testing provides verification. Field sampling offers a snapshot of what is actually delivered to the project. Each layer has value, and together they create a system of checks and balances.

The benefit is confidence. The downside is complexity.

When results differ, it is easy to assume something went wrong in production. Sometimes that is the case. But just as often, the difference can be traced back to how, where, and when the sample was collected. In those situations, we are not necessarily comparing the same material. We are comparing different representations of it.

That distinction matters. From a supplier’s perspective, consistency is not just about producing material that meets a specification; it is about ensuring that the material behaves consistently across the entire supply chain, from tank to truck to roadway. That requires good production practices, but also good sampling practices.

Representative sampling is one of the most important and most overlooked parts of asphalt binder testing.

A properly collected sample should reflect the true condition of the material at that point in time. That means accounting for storage conditions, avoiding contamination, and collecting from a location that represents the bulk material rather than a localized condition. It also means recognizing that timing matters. A sample taken before adequate circulation or mixing may not tell the same story as one taken after.

Without representative samples, even the most precise laboratory test becomes less meaningful. Th is is not an argument against multiple layers of testing. In a system as large and complex as Texas, redundancy is necessary. The scale of production, the distances involved, and the demands placed on pavements require a high level of confidence in material quality. Multiple test points help provide that confidence.

But as an industry, it is worth remembering that more testing does not automatically mean better information. Better sampling does.

The strength of Texas asphalt pavements is built not only on good specifications and advanced testing methods, but also on the fundamentals. Understanding the material. Managing variability. And ensuring that when we test something, we are actually testing what we think we are testing.

Because whether it is a steak on a grill or asphalt binder in a tank, the result is only as reliable as where you put the probe.