In the late 1970s and 1980s my father—working with Professor Stephen Brown at the University of Nottingham—developed a piece of equipment that became known as the Nottingham Asphalt Tester (NAT). It applied a dynamic load to asphalt concrete specimens, typically 150 mm or 100 mm in diameter. The first test they created was the Indirect Tensile Stiffness Modulus (ITSM) test. Using LVDTs, it measured horizontal diametral deformation while a pulsed load was applied along the vertical diameter.

Fast-forward a few decades. Monotonic Balanced Mix Design (BMD) tests have become extremely popular in the U.S. They’re easy to run, the equipment is relatively inexpensive, and the index-based outputs give a fast go/no-go answer. But unlike the ITSM test, these BMD methods do not measure horizontal deformation. The results are based solely on load data.

ITSM itself was created because the Marshall method could not detect certain mix deficiencies that were showing up in the field—especially the stiffness and durability requirements emerging from large-scale, high-temperature projects such as the early Mobil work in the Middle East.

For cracking analysis today, BMD indices are derived from the area under the load–vertical deformation curve and the angle of the post-peak slope. That may be adequate for unmodified binders, but modern mixtures often include RAP, RAS, polymers, fibers, ground-tire rubber, and other additives. The performance contributions of these components are frequently missed by tests such as IDEAL-CT and I-FIT.

Nobody wants to go back to the expensive, complicated performance tests of the early 2000s. Laboratories prefer BMD tests because they already have the equipment and know the procedures. What’s needed is more information about how a mix behaves—without making the test harder or more expensive. Better insight into deformation and crack development leads directly to better predictions of field performance.

Traditional deformation-measurement devices like LVDTs and extensometers aren’t practical for BMD testing: they add cost, they get damaged, and they only measure movement between two points. Digital Image Correlation (DIC) can capture full-field strain and has taught us a great deal in research settings, but it’s expensive, sensitive to setup, difficult to analyze, and typically only records one side of the specimen.

Yet DIC studies consistently show the same thing: specimens reveal far more than the load cell does. Their movement, strain patterns, crack initiation, crack velocity, and failure mode all carry valuable information.

I grew up with the ITSM test in the background—along with AASHTO TP31, ASTM 4123, and other modulus approaches. Measuring deformation makes sense. Measuring it on both sides makes even more sense.

InSight (formerly MiAS) merges the fundamentals of resilient modulus testing with lessons from DIC, facial-recognition algorithms, and self-driving-car vision systems. And just as importantly, it is built around a simple truth: for a method to be adopted, it must be easy to run, reliable, affordable, and genuinely useful.