The New Texas Asphalt

How Texas Built a Better Pavement System

Texas roads still begin with the same basic ingredients: rock and asphalt binder. But over the last several decades, nearly everything surrounding those materials has evolved.

Modern Texas asphalt is the product of decades of collaboration between conractors, suppliers, researchers, educaors, and TxDOT engineers who continuously worked to solve problems, refine specifications, improve testing, and build a system focused on providing an economical, long-lasting pavement.

To better understand that evolution, TXAPA spoke with several individuals who helped shape it firsthand: Dr. Jon Epps, Ph.D., P.E., an asphalt pavement specialist and one of the original architects of the Strategic Highway Research Program (SHRP) research effort; Dale Rand, P.E., executive director of the Lime Association and former head of TxDOT’s Flexible Pavements Branch; Darren Hazlett, P.E., senior engineering scientist at the University of Texas Center for Transportation Research and former TxDOT construction division deputy director; industry veteran Harry Bush, P.E., director, technical services for Vulcan Materials Company; and Robert Lee, P.E., innovation advocacy manager at CRH Americas and former head of TxDOT’s Flexible Pavements Branch.

Together, their perspectives tell the story of how Texas moved from a largely prescriptive pavement system into one built around performance, quality assurance testing, education, and continuous collaboration. And while much of the public simply sees “roads,” the people behind Texas asphalt see an interconnected system involving materials, design, construction, certification, research, and training—all working together to create longer-lasting pavements.

This first installment of “The New Texas Asphalt” focuses on the evolution of materials: liquid asphalt binders, aggregates, recycled materials, testing, and quality assurance. Future installments will examine how Texas transformed asphalt mix design and how education and workforce development continue driving the next generation of pavement innovation.

When Pavements Started Failing

By the late 1970s and early 1980s, asphalt pavements across Texas and the nation were struggling. Truck traffic was increasing, tire technology was changing, and steel-belted radial tires were concentrating heavier loads onto smaller pavement contact areas. The result was widespread rutting and moisture related premature distress that forced engineers and contractors to rethink how pavements were designed, tested, and constructed.

The concerns became significant enough that highway agencies nationwide pushed for a coordinated research effort that ultimately became the Strategic Highway Research Program (SHRP), a massive asphalt binder and mixture research initiative launched in the late 1980s. Dr. Jon Epps was among the individuals involved in developing the original SHRP asphalt research framework, which helped reshape how the industry thought about pavement performance.

One of the major outcomes of SHRP was the development of the Superpave system—short for Superior Performing Asphalt Pavements. The system introduced new approaches to asphalt binder grading, mixture design, and pavement performance testing that focused less on rigid recipes and more on how asphalt performed under real-world traffic and environmental conditions.

Texas quickly became one of the leading states implementing those concepts while continuing to refine its own specifications, testing procedures, and construction practices.

While materials became a major focus, pavement performance depends on more than asphalt binder or aggregates alone. Rand often describes the ideal asphalt pavement as a “three-legged stool” comprised of good design, quality materials, and sound construction.

“If you don’t design it well, for example, then it’s never going to be good, no matter how good the materials are or how good the construction is,” he explained.

That systems mindset became increasingly important as engineers recognized that pavement performance depended on every part of the process working together—from geotechnical design and drainage to material selection, mixture design testing, construction practices, and quality control.

The Asphalt Binder Revolution

As pavement demands increased across Texas, the asphalt industry began moving beyond traditional unmodified asphalt binders toward more engineered, performance-based asphalt binders.

For decades, asphalt binder was often treated as a relatively simple material, the glue holding aggregate together. But according to Darren Hazlett, modern pavement performance increasingly depended on understanding that the asphalt binder itself could dramatically influence how a pavement performed under traffic, heat, moisture, and aging. Hazlett explained. “If the binder is too soft, the pavement can rut. If it’s too hard, it can crack.”

That balancing act became especially important in Texas, where pavement surfaces can become dramatically hotter than ambient air temperatures during summer months while oxidation and aging gradually stiffen pavements over time. Asphalt binder design increasingly became an exercise in balancing competing premature distress: too soft and the pavement could rut or shove under traffic; too hard and it could become brittle and crack as it aged.

Striking that balance became one of the driving forces behind the Performance Grade (PG) asphalt binder system developed through SHRP. Instead of focusing primarily on basic physical properties, the PG system evaluated how binders would perform under specific traffic and climate conditions. The PG system accelerated the use of polymer-modified binders throughout Texas.

“It gives the binder that rubbery property we’re looking for,” Hazlett explained of polymer modification. “It increases stiffness at high road temperatures to help prevent rutting.”

At the same time, engineers increasingly realized that aggregate structure alone could not solve every pavement problem. “We learned that the asphalt binder has a lot to do with rutting and stripping, not just the aggregate skeleton,” Rand explained.

The evolution of liquid asphalt also transformed how quality control worked throughout the industry. Decades ago, TxDOT inspectors were stationed directly at asphalt terminals and refineries, monitoring production and approving shipments.

But as binder systems became more sophisticated and performance-oriented, the industry gradually shifted toward supplier-based quality control systems paired with TxDOT oversight and verification quality assurance testing—a transition that placed far greater responsibility on suppliers to maintain laboratory testing, documentation, consistency, and internal quality control systems.

That transition reflected a broader philosophical shift occurring with asphalt pavements: moving away from highly prescriptive recipe-based specifications toward systems focused on measurable pavement performance. Rather than simply prescribing ingredients, engineers increasingly focused on how mixtures behaved under traffic, moisture, temperature, and time.

Today, many of those same philosophies continue evolving through Balanced Mix Design (BMD), an approach that focuses less on prescribing exact ingredients and more on evaluating how asphalt mixtures perform through laboratory testing. Rather than relying solely on traditional volumetric properties, BMD attempts to balance competing pavement distresses such as rutting and cracking—a concept that closely mirrors the balancing act Hazlett described for asphalt binders.

Meanwhile, asphalt binder research continues to evolve. Hazlett noted that researchers increasingly focus on slowing oxidation and long-term aging, so pavements remain flexible longer into their service lives. “If I can add something to the binder so it doesn’t age as much, then I can postpone the day when it becomes too stiff and starts cracking,” he explained.

The Aggregate Revolution

During this time, the aggregate industry was also undergoing a transformation. According to Harry Bush, the trajectory went from simply supplying rock into engineering highly specialized structural systems designed for specific pavement applications.

“It’s still rock coming out of the ground,” Bush explained. “But we are doing things differently.”

Earlier generations of asphalt mixtures often relied heavily on finer gradations that lacked strong internal aggregate structure. “A lot of the older mixes were sand-on-binder,” Bush said. “You hadaggregate, then a lot of sand and binder filling in the gaps.”

As Superpave concepts emerged through the SHRP era, Texas increasingly moved toward mixtures emphasizing stone on stone contact, where larger aggregate particles interlock and carry traffic loads more effectively.

“That stone-on-stone contact gives strength, so it doesn’t rut,” Bush explained. “And the asphalt binder film thickness is increased around the aggregate giving it durability and flexibility, so it doesn’t crack.”

Implementation of the Hamburg Wheel Tracking (HWT) test in the late 1990s proved to be a game changer in predicting longterm HMA field performance. In the laboratory, the HWT identifies HMA mixes prone to premature rutting or stripping, helping prevent poorperforming mixes from being placed on Texas roadways.

Through the HWT, the industry learned that aggregate performance varied dramatically depending on source and application. River gravels, for example, offered excellent hardness and skid resistance but historically raised stripping concerns because asphalt binder struggled to adhere to their smooth surfaces.

“The asphalt binder on some gravels is almost like asphalt stuck to glass,” Bush explained. “You could almost get your fingernail under it and peel it off.” The HWT demonstrated that lime and other additives could be used to greatly reduce stripping concerns.

Beyond validating the benefits of lime in HMA, the HWT also drove major advances in anti-strip additives, moisture susceptibility testing, and binder chemistry. At the same time, Texas placed increasing emphasis on longterm skid resistance through expanded use of SAC A aggregates—harder, polish-resistant materials capable of maintaining micro-texture surface texture under traffic.

“The whole theory is that the SAC A doesn’t polish down as much,” Bush explained. “You end up with better micro-texture from the aggregate and macro-texture from the mix that gives you improved skid resistance.

Aggregate quality control evolved dramatically as modern testing methods such as the Micro-Deval allowed producers to evaluate durability far faster and more accurately than older testing procedures. “It’s a quick way to determine whether your material is going to meet quality standards,” Bush said. Meanwhile, quarry operations themselves became increasingly sophisticated. Modern aggregate operations now rely heavily on geology teams, coring programs, digital mapping, and three-dimensional modeling to understand material quality before blasting even begins.

“We used to just blast a shot and see what we got,” Bush said. “Now we know what it’s going to be before we mine it.”

That same philosophy of material stewardship eventually extended into recycled materials as reclaimed asphalt pavement (RAP) usage increased throughout Texas. Contractors and agencies began recognizing that recycled pavements contained valuable aggregate and binder resources that could be carefully managed and reused rather than treated as waste.

According to Robert Lee, the industry’s thinking fundamentally changed when RAP stopped being viewed as a disposable byproduct and started being treated as an engineered material stream. “We stopped treating it like a waste product and started treating it like an asset,” Lee explained.

That shift led to major improvements in stockpile management, fractionation, contamination control, and preservation of premium aggregate materials. Instead of indiscriminately blending reclaimed materials together, producers increasingly separated materials by source and performance characteristics so highquality aggregate resources could retain their value.

“If we know what’s in it and we know the properties of it, then we’re okay using more of it,” Lee said.

In many ways, RAP management became the natural extension of the broader evolution occurring throughout the Texas asphalt industry: greater intentionality, better testing, improved data, and more sophisticated stewardship of materials.

The Role of TXAPA and the Hot Mix Asphalt Center

While technical advances reshaped materials and specifi cations, another equally important transformation was occurring. Over the last several decades, Texas built an intentionally collaborative relationship between the industry and TxDOT— one that many participants believe became one of the defi ning strengths of the state’s asphalt pavement program.

According to Dr. Epps, that collaboration matured through multiple interconnected systems: the TXAPA Annual Meeting, steering committees, working groups, certifi cation programs, and ongoing educational initiatives.

The creation of the Hot Mix Asphalt Center (HMAC) became one of the most important milestones in that evolution. As QC/QA specifications shifted greater responsibility onto contractors and suppliers during the late 1980s and early 1990s, the industry needed standardized technician training and certifi cation systems capable of supporting the increasingly sophisticated testing and quality control environment.

The result was the development and delivery of certification programs covering asphalt binders, aggregates, soils, bases, and asphalt mixture testing in hot mix asphalt.

“It’s a big deal,” Epps said of the certification program. “The certification program and the specification changes have and continue to influence the quality of hot mix.”

The system helped create a shared technical language between contractors, suppliers, consultants, and TxDOT personnel across the state. Over time, recurring steering committees and working groups brought industry partners and TxDOT together quarterly to address emerging pavement issues collaboratively rather than relying on isolated specification changes or one-time research projects.

“It’s not a one-and-done thing,” Epps explained. “It’s a continuous process.

Paving the Way Forward

Today’s asphalt pavements in Texas are the result of decades of refinement across every part of the system—design, materials, testing, construction, certification, research, and education.

Specifications continue evolving. Asphalt binder technologies continue advancing. Aggregate systems continue improving. Recycling practices are becoming more sophisticated. And educational programs continue training the next generation of technicians, engineers, and pavement professionals.

But perhaps the most important evolution was not technical at all.

Texas built a culture where knowledge continuously circulates between researchers, contractors, suppliers, educators, and agencie —a system where problems are studied collectively, lessons are shared openly, and improvements are constantly refined through collaboration.

That culture will be the reason Texas asphalt continues evolving.