Texas’ transportation system has allowed the state to successfully compete in a global market. An efficient transportation network allows companies to move their goods efficiently and effectively, offering just-in-time service to their customers.
In the current economic climate, the agencies that oversee our transportation system must make every dollar count. This renewed focus means using the right maintenance technique on our roadways at the right time. And knowing just what that technique should be takes solid research.
The Texas Transportation Institute (TTI) is finding innovative and cost-effective ways to maintain and rehabilitate our infrastructure. Though cash-strapped agencies are less inclined these days to build new facilities, construction is still underway on some critical projects. With billions of dollars at stake, these agencies need TTI‘s research to ensure they’re spending their dollars wisely.
“Infrastructure” in the context of transportation includes our roadways, bridges, traffic control and information devices, safety hardware, drainage structures, and other structures on the right-of-way. The current shortage of tax dollars to maintain that infrastructure might, on first glance, suggest that we should back off our preventive maintenance and rehabilitation measures until the economy recovers. But the long-term cost to Texas and the nation could be staggering. Reconstruction of infrastructure can cost more than four times as much as preventive maintenance and rehabilitation. When you’re looking at dollar amounts in the billions, it’s obvious that we can’t put off the bill until later.
TTI‘s research on roadways includes planning, construction and maintenance. “Not only do we need to build new facilities that last longer,” says Andrew Wimsatt, head of TTI‘s Materials and Pavements Division, “we need to improve the life expectancy of existing facilities. One way TTI does this is through helping improve material specifications and practices, optimizing the use of what we have and stretching our dollars.”
The Texas Department of Transportation (TxDOT) has had an aggressive preventive maintenance program since the 1980s. In 2009, TxDOT spent $1.2 billion to maintain or rehabilitate 192,150 lane-miles of roadway. With the current budget shortfall, TxDOT may have to make some hard decisions about the level of maintenance it’s able to provide.
In cooperation with The University of Texas at Austin, TTI operates the Pavement Preservation Center, which teaches classes on pavement preservation strategies and how to fix the right road at the right time with the best treatment. Another way TTI is helping TxDOT evaluate its repair and rehabilitation needs is by developing tools to help in that decision-making process. Based on the condition and history of the roadway, software developed by the Institute can suggest the best strategies — ranging from seal coating to full-depth reclamation.
TTI is also helping TxDOT detect what causes deterioration, which helps reduce needed repairs down the line. “If you put a thin hot-mix asphalt overlay on a roadway that has structural defects, the problem will quickly return, and the life-cycle cost will be high,” says Jon Epps, TTI executive associate director. Preventing deterioration reduces the need for costly repairs later, saving potentially millions of dollars over time.
Over the last 15 years, TTI has developed and improved a wide range of nondestructive testing techniques to predict pavement conditions, such as ground-penetrating radar. More recently, TTI researchers developed the prototype for an infrared temperature bar system called Pave-IR, which allows contractors to correct their construction practices in real time. The technology has been commercialized, and several TxDOT districts have used the system with contractors on construction jobs.
Sustainability is an important area of infrastructure research. As applied to roadways, sustainability can mean many things. It can mean reusing and conserving existing roadway materials through innovative rehabilitation techniques such as full-depth reclamation. It can mean using materials and processes to reduce emissions and greenhouse gases during construction (e.g., using warm-mix asphalt rather than hot mix). It can also mean reducing the energy associated with maintenance and rehabilitation projects by doing them less often or selecting more energy-efficient alternatives.
Safety is another key aspect of TTI‘s research to improve our infrastructure. According to Wimsatt, dangerous potholes are not the only safety factor we have to worry about on our roadways.
“Skid resistance is also important,” he says. “Our research helps improve skid resistance, keeping cars on the road where they belong. We also aim to design pavement mixes to resist rutting, which will help to keep water off the road. We all know the dangers of hydroplaning.”
Bridges and Other Roadway Structures
As some of the costlier components in the transportation system, bridges require special attention to maintenance.
“TTI research into bridges and structures focuses on selecting the right maintenance or repair technique,” says Gene Buth, TTI assistant agency director and Texas A&M University senior Research Fellow. “For example, just because a structure has cracking on the surface does not mean that it’s structurally unsound. Conversely, structures that look good on the surface are not necessarily structurally sound.”
Many TTI projects have investigated alkali-silica reactivity and delayed ettringite reaction, detrimental chemical reactions in concrete, which can cause serious problems for concrete structures. Specifications for materials and methods now prevent or reduce these reactions in concrete, and research is continuing to determine the structural integrity of those older structures that exhibit some cracking. Not all structures will need costly repair or rehabilitation — again, the right technique at the right time can save transportation agencies millions or even billions in unnecessary repair bills.
Rehabilitation techniques also apply to scour, which is the loss of sediment from around bridge abutments or piers. Scour can compromise the integrity of a structure if not remediated.
“Historically, Texas has been overly conservative in estimating bridge scour,” says TTI Research Engineer and Texas A&M Professor of Civil Engineering Jean-Louis Briaud. Briaud also manages TTI‘s Geotechnical and Geoenvironmental group. “We have estimated for the worst-case scenario, but scour may be different depending on the type of soil underlying the structure. We are developing techniques to accurately predict scour so that transportation agencies can build more cost-effectively.”
Developed by TTI, the Erosion Function Apparatus (EFA) can accurately measure a soil’s susceptibility to scour. Not only does this information go into design and maintenance planning, but tools like the program MEANDER use this information to predict how rivers migrate and how we need to react to the shift.
For new construction, TTI is helping develop and test new, lower-cost techniques. Splicing prestressed beams may cost less and allow concrete structures to compete with steel over longer spans. Precasting panels for bridge overhangs is also a quicker, low-cost technique and eliminates the safety issues of installing overhangs cast in place.
“The cooperative relationship we have with our sponsors is what gives our research impact,” says Paul Krugler, TTI research engineer. “For example, transportation agencies don’t have the time and personnel to try out and fully evaluate many of the new techniques developed elsewhere in the United States and the world. TTI serves that purpose. We listen to what they need, whether it’s to evaluate a new technology for application in Texas or to develop a brand new technology. We apply sound technical principles and methodologies, and then we give a high return on invested research dollars. About 10 years ago TxDOT estimated their rate of return on research at five times what the department spends. I think that’s a conservative number.”