By: Chris Pourteau
Roads were, arguably, the single most important engineering achievement in the Roman Empire.
They connected population centers—those oases of Roman culture and civilization—across great expanses of deadly wilderness. Roads facilitated commerce and made it possible to move Roman legions relatively quickly to wherever they might be needed. Because of their singular importance to the empire, road repair was not only a practical necessity, but also a civic duty in Rome.
A stretching exercise
The essential function of a road remains unchanged. In fact, when President Eisenhower sold the country on his landmark Interstate Highway System in the 1950s, he explained how it would get the farmer “out of the mud” and to market more efficiently while also facilitating movement of military troops in wartime. He might have been a member of the Roman senate, arguing for construction of the Appian Way.
Thanks to Eisenhower’s vision, urban (and suburban) areas have grown over the past half-century to become the hubs of our own civilization—connected by roads (and rail and air). And while we don’t face gothic tribes waylaying caravans between cities, the requirements of a world economy make maintaining roads just as vital 2,000 years later.
Growth in urban areas since the 1950s has required increased road capacity as more people driving more vehicles attempt to use the same number of lanes and roadways. Through the end of the 20th century, the country’s traditional response to this need was simply to build more roads or widen existing corridors. As more and more demands were placed on roads designed to a specific capacity standard, many instances of earlier-than-expected pavement failures occurred.
Besides the rising costs associated with fixing these failures, road maintenance does not occur in a vacuum; timely repair activities significantly affect pavement longevity. And as local, state and national economies have shrunk, agencies have had to learn to make better strategic decisions regarding pavement repair and upkeep. These days, highway agencies must closely examine their overall maintenance/repair/rehabilitation strategies to most efficiently spend their shrinking budgets.
“Doing more with less” is the overriding consideration driving rehabilitation strategy development, since there is a continual need for cost-effective pavement rehabilitation solutions. Finally, as the highway system ages, it will need more consistent repair over time.
“In short, better decision making that facilitates more timely repairs is key to stretching maintenance dollars, slowing down the rate of deteriorating roadways and implementing the most appropriate solution to a given problem,” said Dan Zollinger, manager of the Texas Transportation Institute’s (TTI) Rigid Pavements Program.
Weakness watch
Shrinking budgets, the increased use of roadways, older highways and more roadways to maintain require a systematic, methodical approach to selecting appropriate maintenance and rehabilitation strategies. Introducing continuity relative to early distress indicators to condition assessment and treatment selection helps create longer-lasting, cost-effective rehabilitation strategies. Settling on a consistent nomenclature for classification improves the likelihood that maintenance personnel will match the right repair method to the right need.
“One of the most important factors in properly diagnosing repair needs is experience in the field,” explained Zollinger, principal investigator on the project.
Usually, however, retirees take their experience with them when they leave an agency. Thus, the need to capture best practices from these experienced professionals is vital to bridging the gap between textbook solutions that don’t always match real-world problems and, say, 10 years worth of field experience.
TTI conducted Texas Department of Transportation (TxDOT) project 0-5821, titled “Develop Guidelines for Routine Maintenance of Concrete Pavement,” to address these issues. The project had the following objectives:
- Identify portland cement concrete (PCC) pavement distresses that require preventive maintenance;
- Provide a list of pavement repair methods as well as a description of them, their associated effectiveness and how they are used;
- Provide guidelines on how to formulate optimum repair strategies to minimize repair costs and maximize pavement life;
- Provide repair detail sheets and special specifications to support the optimization process; and
- Provide training materials to implement the products of this project.
Generally speaking, the project focused on identifying early maintenance opportunities for pavements. Earlier, less invasive maintenance procedures often equate to reduced long-term maintenance costs and improved roadway life span. To be able to accurately and reliably diagnose the causes of early deterioration, field engineers need a common system for observing, classifying and determining the best solution to pavement failures. Since early diagnosis relies heavily on visual inspections, using a falling-weight deflectometer (FWD), ground-penetrating radar (GPR) or a dynamic-cone penetrometer (DCP) can help identify opportunities for early interventions.
The research team developed “Guidelines for Routine Maintenance of Concrete Pavements” to present these issues in a user-friendly, practical field manual for use by pavement engineers.
“Applying these guidelines can help local districts use early detection of potential failures and repair them efficiently,” explained Tom Freeman, engineering research associate at TTI, who developed the guidelines. “Specifically, these procedures teach engineers how to recognize poorly performing pavements, classify the kind of distress observed and determine the best repair method for a given problem.”
In addition to the guidelines, the team developed a field survey and repair-decision flowchart to guide engineers in their decision making. These products take years of practical engineering experience and make it useful to less experienced practitioners.
Based on the information
The research team developed a field survey to evaluate the effectiveness of full-depth repair, various joint repair techniques, joint resealing and dowel-bar retrofit with diamond grinding.
The survey gathers information regarding the pavement maintenance problem to help field engineers classify the kind of distresses they have observed in the pavement in question. Information gathered includes the following:
- General information about pavement: age and aggregate type;
- Condition record information: recent visual and deflection information;
- Condition of joint or crack sealing;
- Surface and subsurface drainage condition: possible locations for GPR and DCP testing;
- Functional conditions: factors affecting riding quality and possible locations for FWD, GPR and DCP testing;
- Structural conditions: factors affecting premature failure of pavement and possible locations for FWD, GPR and DCP testing; and
- Identification of distressed areas for FDR.
Let the answers flow
The repair-decision flowchart provides guidance for proper, effective routine maintenance of jointed concrete (JC) pavement, continuously reinforced concrete (CRC) pavement and asphalt concrete (AC) overlaid jointed concrete pavement. The flowchart comprises five levels of decision making: performance monitoring, preservative, functional concrete pavement repair (CPR), structural CPR and removal and replacement of pavement when necessary. The decision levels progress from simple solutions to maintenance issues to more invasive options.
Performance monitoring, perhaps the most important level, is about gathering basic data on a pavement segment and determining the possible next steps for assessment, beginning with visual inspection. The second level of decision making, preservative, involves identifying a particular, relatively minor treatment to minimize potential moisture damage and assessing joint and crack seals and edge drains that might need more attention. Functional CPR is a short-term solution for dealing with localized distresses or overall ride-quality problems. The fourth level, structural CPR, eliminates the cause of structural distresses and requires retrofitting structural-joint capacity to extend pavement service life. Sometimes, functional and structural CPR are combined to deal with a range of common problems. And finally, remove and replace is exactly what it says—removing and replacing the pavement section while putting precast concrete panels in place to reduce traffic congestion during the replacement process.
A pocket of guidance
As described earlier, the pocket field manual provides a standard for maintenance crews to use in assessing, describing and repairing the maintenance challenges they encounter. Enhanced by photographs showing the different kinds of concrete distresses, the manual leads field personnel through the possible causes, recommended lab tests and repair procedures.
The manual includes three main areas:
- Nondestructive test procedures for subsurface layers, such as FWD and GPR;
- Discussion on each maintenance stage, promoting the best standard practices and specifications used by state departments of transportation across the U.S.; and
- A step-by-step repair method and decision-making process to point engineers in the right direction: preventive maintenance, functional or structural concrete pavement repair or full resurfacing.
Sturdy and functional in design, the manual is tailor-made for use in the field, where on-site inspection of failures is a must for proper identification, diagnosis and repair.
Diagnosis dialogue
To optimize maintenance dollars in a time when some state economies are going bankrupt, properly diagnosing pavement failures—their causes and best solutions—is vital. TTI, through TxDOT’s project 0-5821, has created a common language for field engineers to use in describing pavement degradation and repair, thereby increasing maintenance efficiency, consistency and cost effectiveness. The improved diagnostic tools resulting from the project can lead field personnel to more accurate diagnoses of problems, which in turn help yield more appropriate, cost-effective interventions. Perhaps the most important aspect of these tools is in transferring knowledge from experienced engineers to those just entering the field.
“This research defines another set of tools for TxDOT engineers to economically maintain pavements on an aging transportation system with decreasing funding,” said TxDOT’s Paul Montgomery, director of maintenance. “These tools help us along the path of progress in pavement management.”
About The Author: Pourteau is a senior research editor with the Texas Transportation Institute.
