Paving the Way, July/August 2002 Public Roads

Paving the Way
by J. Mauricio Ruiz, Robert Otto Rasmussen, and Patricia Kim Nelson

Constructing concrete pavement that requires less maintenance, saves money, and reduces traffic disruptions is the ultimate feat—the pot of gold at the end of the rainbow. Helping achieve these goals, HIPERPAV software is a user-friendly, Microsoft Windows® -based computer tool that uses dozens of models to predict the early-age behavior of pavements, which influences long-term performance and durability. Using this state-of-the-art software, pavement planners, designers, and contractors can make smart decisions to ensure high performance over the short-and long-terms.

With a wide range of applications, HIPERPAV is used during the planning stage to develop specifications for quality control based on the available materials and climatic conditions of the region where the roadway will be constructed. Designers use HIPERPAV to optimize their pavement designs to produce a better end product and long-term performance, while maximizing economy. Contractors use HIPERPAV to help prevent expensive repairs by predicting potential damage and determining the best set of variables to forestall damage.

“HIPERPAV is a valuable tool for State departments of transportation, counties, municipalities, private owners, and contractors alike,” says Steven Healow, pavement and materials engineer at the Federal Highway Administration’s (FHWA) California division in Sacramento. Healow’s satisfaction with the product led him to adopt the use of HIPERPAV on all of his large-scale pavement projects that use portland cement concrete, including major rehabilitation projects on I-10, I-15, I-80, and I-5.

To open up newly constructed pavements within days or hours after the work is completed, pavement contractors in the early 1990s used “fast-track” concrete mixes that gain strength rapidly but can be damaged severely if placed under adverse weather conditions. In response to this problem, FHWA initiated research on the development of construction guidelines for fast-track jointed plain concrete pavements (JPCP).

The research, awarded in 1993 to The Transtec Group of Austin, TX, aimed to maximize the performance of fast-track pavement through proper design, selection of pavement materials, construction, and environmental factors. Another goal was to develop an understanding of how fast-track concrete’s high heat of hydration (a chemical reaction during setting) interacts with pavement curing methods, environmental conditions, and design criteria. Above all, the project aimed to translate the research findings into a usable tool for wide-scale, practical, and immediate application in the field. And so HIPERPAV was born in 1996.

HIPERPAV models the complex interactions between four factors during the first 72 critical hours after construction: pavement materials, design, construction, and climatic conditions. These factors are key to the production of durable concrete pavements.

The core of the HIPERPAV system is a robust model for prediction of pavement temperature and moisture changes. Stresses in the concrete and gain in strength are projected based on temperature, allowing the identification of scenarios in which damage may occur in the pavement structure. For jointed concrete pavement, early-age damage is the development of uncontrolled cracks. By changing the input parameters to the model, HIPERPAV enables users to identify the set of conditions that lead to optimum performance.

In addition to temperature, HIPERPAV predicts moisture changes during the first hours after construction. Temperature and moisture changes act together to cause significant changes in volume that can in turn produce curling and warping in conjunction with axial restraint (restrictions to movement) at the slab-subbase interface. By identifying these risks, HIPERPAV enables users to implement an alternative design to prevent pavement damage.

The HIPERPAV predictions are used to model uncontrolled mid-slab cracking in the early-age of JPCP. Two scenarios of stress-versus-strength development can occur. When stress maintains a magnitude consistently lower than strength, early-age distress is not expected; when stress develops at a much greater rate than strength, a failure may occur in the form of a crack.

"When it comes to pavement cracking, HIPERPAV is very helpful in piecing together various parts of the puzzle to analyze the root causes," says Robert Prisby, director of paving services for Western Pennsylvania American Concrete Pavement Association (ACPA), Northeast Chapter. "With anywhere from 30 to 40 factors that can contribute to cracking," adds Prisby, "HIPERPAV helps users focus on the real issues of concern, either by highlighting possible causes that developed in the early ages, or by eliminating them and allowing users to concentrate instead on stresses and loading that occur in later stages." Prisby has used HIPERPAV in a variety of applications, including airports, highways, and one busway.

In addition to these predictive abilities, the software developers added modules for predicting the potential of early-age damage to JPCP and bonded concrete overlays, guidelines for timing contraction joint sawing, guidelines for early traffic loading of JPCP, and evaporation rate guidelines to predict the potential for moisture loss in portland cement concrete pavements.

HIPERPAV uses a synergistic strategy known as a total systems approachto integrate the new modules with the core software, so that it can serve as a critical tool during all stages of the paving process. Planners and designers can use HIPERPAV in office settings to develop quality control specifications for particular projects. Contractors in the field can use it during construction to modify input parameters according to climatic conditions. With this flexibility, HIPERPAV can optimize pavement designs and help prevent expensive repairs.

“Analytical tools like HIPERPAV can be useful in avoiding situations that cause distress, such as plastic shrinkage cracking or excessive moisture loss in new pavement,” says Healow, who is using HIPERPAV on concrete paving projects in California’s Mojave Desert, where the combination of high temperature, high wind velocity, and low humidity create some of the worst paving conditions in the country. “Our successful construction of portland cement concrete pavements in a desert environment depends on how well our slabs cure and gain strength,” he says. “With HIPERPAV, we can assess and minimize the risk associated with our mix design, construction methods, and curing methods to avoid risky situations.” HIPERPAV can serve as an educational tool and can be used in assessing the causes of pavement damage or poor pavement performance in forensic (liability) studies.

Each of the models that make up HIPERPAV underwent extensive calibration and validation using field data. HIPERPAV proved itself in a wide range of pavement designs, materials, and climatic conditionsduring full-scale validation in Arizona, Minnesota, Nebraska, North Carolina, and Texas. This process included the instrumentation of pavements under construction to allow for direct study of early-age behavior. In collaboration with highway departments in each State, researchers validated the accuracy and reliability of HIPERPAV in the prediction of stresses, concrete strength development, and crack susceptibility.

The original HIPERPAV system was implemented in the field on a number of occasions. During the implementation phase, a technical working group of paving experts applied HIPERPAV to in-place and upcoming paving projects. Examples of HIPERPAV successes in predicting early-age behavior include:

To demonstrate HIPERPAV andinform contractors, academicians, and representatives of State departments of transportation about the importance of early-age behavior, FHWA sponsored a series of HIPERPAV workshops throughout the United States in the late 1990s. The workshops captured the attention of local government agencies, private industry, and educational institutions. By taking a unified approach, FHWA, Transtec, and the American Concrete Pavement Association achieved notable success in implementing the software.

Now that HIPERPAV has proven itself with users and demand for thesoftware has increased throughout the industry, the software developers are improving and expanding it to include a module capable of predicting the impact on JPCP long-term performance as a function of early-age behavior, a module capable of predicting the early-age behavior of Continuously Reinforced Concrete Pavements (CRCP), and modules to incorporate results from existing FHWA studies related to concrete paving.

Experienced practitioners have long recognized that a number of early-age mechanisms determine how pavements will perform in the long term. Factors such as joint opening, drying shrinkage, thermal gradient at set time, and portland cement concrete relaxation (i.e., the release of stress) play important roles in long-term pavement response and performance. These early-age mechanisms have an effect on load transfer efficiency at the joints and cracks, affect the stress state in the pavement, and consequently contribute to pavement distress.

The software developers are modifying HIPERPAV to include new algorithms that will simulate the effects of these early-age factors on long-term pavement performance. By using the JPCP long-term module in HIPERPAV, users will be able to predict structural and functional distresses such as faulting, cracking, andriding quality. With this knowledge, users can implement alternative designs to minimize negative effects on pavement performance.

Continuously reinforced concrete pavement (CRCP) refers to concrete pavement that is reinforced with steel and constructed without transverse contraction joints. In this type of pavement, concrete cracks randomly as a consequence of volume changes (from temperature and moisture variations) that are restrained by both steel and the sub-base. If crack spacing, crack width, and steel stress are controlled to fall within certain limits, long-term performance is not compromised.

Previous research efforts developed sound mechanistic models that are capable of predicting crack spacing, crack width, and steel stress in CRCP pavements. To ensure superior long-term performance, the new HIPERPAV module will incorporate prediction models for CRCP behavior, so that users can better evaluate design alternatives.

The HIPERPAV software developers selected two studies sponsored by FHWA for incorporation into additional new modules. The first study focused on using advanced statistical techniques to optimize concrete mix designs to meet specific performance criteria, such as slump, strength, and cost. Previously developed by FHWA in cooperation with the National Institute of Standards and Technology (NIST), this effort computerized the process of optimizing mix design on a Web-based application. As part of the enhancement of the HIPERPAV system, the developers are converting the FHWA-NIST procedure to a PC environment."

The second study looked at the early-age behavior of dowel bars in rigid pavement. One of the major rehabilitation costs for pavements is the repair of prematurely deteriorated transverse contraction joints that can result from lack or improper placement of dowels (tube-like bars that tie concrete sections together). Using dowel bars instrumented with strain gauges, Ohio University conducted an experimental study to evaluate the response of dowel bars in rigid pavements under field traffic loads and environmental conditions.

The study found that during the critical first 72 hours after construction, the concrete around the dowels is subjected to stress when the dowels bars resist the natural upward and downward curling of concrete. Since the concrete has not yet reached its full strength at this time, it could be damaged at the dowel-concrete interface. As the dowel cycles through subsequent repeated environmental and traffic loading, the damage to the concrete at the interface will increase. Eventually, the concrete can spall (i.e., chip at the surface) or crush. The dowel bar-concrete bond can loosen and cause the joint load transfer efficiency to decrease. HIPERPAV’s dowel analysis module will predict stress development and allow for appropriate design decisions with regard to the placing of dowels.

Using a total systems approach, the various components of HIPERPAV will be integrated easily with new modules. At the core of the enhanced system will be the original HIPERPAV system that predicts temperature and key portland cement concrete behaviors. The new modules will radiate from the core. In some cases, modules may be interrelated. For example, the early-age JPCP module will drive the long-term performance module for JPCP.

To keep HIPERPAV easy to use and allow for future model upgrades, the software developers created a new graphical interface for a more seamless integration of the various modules. HIPERPAV’s new front-endgroups categories of inputs in a directory-like structure along the left side of the screen. The software was modified to include error-checking routines, tool tips, additional user input unit options, and more user input graphical aids.

Incorporation of new models mean that validation will be needed. The software developers have investigated new field sites for this purpose. They have implemented a laboratory program to collect the critical material inputs needed by both the HIPERPAV core and the additional models under study.

Completion of the enhanced HIPERPAV is expected by the fall of 2002. To demonstrate the advanced HIPERPAV and inform possible users of its new applications, FHWA is planning technical support, training sessions, and workshops, similar to those that introduced the original version.

1. Forster, Stephen W. “HIPERPAV: A User-Friendly Tool to Help Us ‘Build It Right,’ “ Public Roads, April/May 1998.
2. McCullough, Frank, and Robert Rasmussen. Fast-Track Paving: Concrete Temperature Control and Traffic Opening Criteria for Bonded Concrete Overlays, Volume I: Final Report, FHWA-RD-98-167. October 1999.
3. Sargand, S. M. Performance of Dowel Bars and Rigid Pavement. Department of Civil and Environmental Engineering. Ohio University. FHWA and U. S. Department of Transportation. July 2000.
4. Simon, Marcia et al. Concrete Mix Optimization Software Tool, User’s Guide, NIST, FHWA, July 2001, from http://ciks.cbt.nist.gov/cost/.
5. Simon, Marcia et al. Concrete Mixture Optimization Using Statistical Mixture Design Methods, Proceedings of the PCI/FHWA International Symposium on High Performance Concrete, New Orleans, Louisiana, October 20–22, 1997.

J. Mauricio Ruiz received his B.S.C.E. from the Univ. Michoacana de S. Nicolas de Hidalgo, Mexico, and an M.S.E. in civil engineering from the University of Texas at Austin. He was in charge of the field validation and technical implementation for the first generation of HIPERPAV. He is currently a project manager at The Transtec Group, Inc., in Austin, TX, and co-principal investigator for the new HIPERPAV system analysis software.

Robert Otto Rasmussen is vice president and chief engineer of The Transtec Group. Along with Ruiz, he serves as CO-principal investigator for the HIPERPAV program. He received his B.S. in civil engineering from the University of Arizona, and MSE and Ph.D. from the University of Texas at Austin. He is active in several organizations, including TRB (A2B02 and A2F01), the American Concrete Pavement Association (ACPA), the International Association for Building Materials and Structures’ (RILEM) Technical Committee on Bonded cement-based material overlays for the repair, the lining or the strengthening of slabs or pavements (RLS TC), and ASTM International. He is a registered professional engineer in Texas.

Patricia Kim Nelson received her B.S.C.E. From Texas A&M University and an MSE and Ph.D. in civil engineering from the University of Michigan at Ann Arbor. She is an expert in the field of fiber-reinforced concrete and pavement analysis. Working along with Ruiz and Rasmussen, she validated the first generation of HIPERPAV and currently is participating in the development of the new HIPERPAV software. She is a project manager at The Transtec Group, Inc.

To learn more about HIPERPAV, please visit www.hiperpav.com or e-mail Mauricio Ruiz at mauricio@thetranstecgroup.com.