U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
|This report is an archived publication and may contain dated technical, contact, and link information|
|Publication Number: FHWA-HRT-11-065 Date: April 2012|
Publication Number: FHWA-HRT-11-065
Date: April 2012
Construction considerations include issues related to equipment, construction operations, and QC.
Many key elements that can make or break a concrete paving project are related to construction operations. Although significant emphasis is placed on planning, designing, and selecting materials for a concrete pavement, several elements of construction operations can also impact the overall quality of the pavement.
Concrete pavements will be built, rehabilitated, and maintained in way that minimizes negative impacts on the public, meets expected design requirements reliably, and provides immediate quality feedback during operations.
This goal can be reached by accomplishing the following research objectives:
As with pavement design and materials/mixes, the relationships among various elements and variables of pavement construction should be understood and demonstrated mathematically to optimize pavement performance. Ultimately, users drive construction requirements because they dictate the functional demands and essentially own the facility. Each project starts with basic variables, such as location, which dictates material availability, weather conditions, and construction windows, among other things. When combined, these basic variables dictate construction schedules and available mix alternatives, which, in turn, dictate the required construction techniques. Construction techniques influence the construction process and ultimately the as-constructed pavement. The as-constructed pavement has certain functional characteristics, which ultimately are accepted or rejected by users. While users do not actually make the decision to accept a finished product, they can apply the political pressure that will ensure their demands are met.
The following pavement construction issues are addressed in various tracks of the CP Road Map.
Highway users are less tolerant than ever of the temporary inconvenience that highway construction often brings. Innovative techniques are needed for both assessing the impact on the public and optimizing traffic mitigation during construction operations. Computerization is expected to assist in this goal, but additional work needs to be done before reliable optimization methods are adopted.
For contractors, the sequencing and timing of operations also need to be optimized. Contractors commonly face limited resources, including equipment and labor. Techniques should optimize the use of these resources to expedite construction operations at minimal cost. Closely related to this is the demand for more rapid concrete mixing and placement techniques. It has been demonstrated that even modest improvements in concrete placement production rates can significantly accelerate the construction process.
Finally, future research should include cutting-edge technologies, such as precast and prefabricated construction. These technologies have begun to show promise as a means to accelerate construction under certain circumstances.
Public agencies are becoming more sensitive to the quality of concrete pavements immediately and soon after construction. Several technical challenges, however, limit understanding and control of the numerous elements affecting initial quality. Existing products, such as FHWA’s HIPERPAV® (HIgh PERformance Concrete PAVing) program, show promise as tools to accomplish this goal, but additional work is needed. Future research should address a number of these challenges, using a systems approach to recognize their connection with other elements.
The factors that impact initial quality the most are related to temperature and moisture management. Concrete is a dynamic material, with several complex processes occurring simultaneously in a dynamic environment. The interaction of these variables can often lead to unexpected temperature and moisture conditions in the new concrete slab. These conditions, if severe enough, can compromise the initial quality of the pavement, which can ultimately impact long-term performance. A number of construction operations elements can also affect the temperature and moisture of the concrete, and additional work is needed to understand this complex process.
Other construction variables have also been identified as having an impact on initial pavement quality. For example, the consolidation of concrete as a function of vibration methods can affect dowel-concrete interaction, air void structure, and other factors. Saw cutting is also important. Selecting optimum depth and timing of saw cutting operations for a particular project are still insufficiently understood.
Variability is arguably the most important element that can impact overall initial pavement quality. Variability is inherent in every aspect of a pavement, including design, materials, environment, and construction. The impacts of construction variability especially need to be better understood. If too much emphasis is placed on controlling the variability of a particular construction aspect, additional cost is introduced into the system. If not enough emphasis is placed on controlling variability, however, the quality of the product can suffer.
Most experts agree that concrete pavement quality is impacted significantly by the quality of construction operations. With pressure to shorten the paving operation window and use lessthan- desired materials, the room for error expands. One of the most critical aspects of concrete paving in the future will be rapid and continuous feedback on the numerous variables that drive quality. Variability in weather, support conditions, and concrete material quality ultimately will lead to variability in the end product.
A new concept, ICSs, could be the solution. First publicized in preparing the Future Strategic Highway Research Program (SHRP) Rapid Renewal Proposed Scope of Work, ICS is closely related to the way intelligent transportation systems help traffic engineers better manage traffic. ICS similarly will allow contractors to better control paving operations. ICS includes the rapid and continuous feedback of measurement data related to pavement quality and provides tools to make necessary corrections with predictable results. Before ICS can be fully advanced, however, a host of more fundamental research should be accomplished. ICS can improve contractor process control, improve and permanently record QC data, and integrate with asset management/PMSs.
NDT of concrete pavements is fundamental to the ultimate success of ICS and warrants extensive study and application. NDT has been used successfully, although not widely, to understand the in situ strength and durability of concrete pavements. A number of techniques are available to predict the properties of early-age concrete shortly after construction, but each technique has inherent benefits and limitations. Future research should further evaluate the use of NDT as a means to assess concrete quality rapidly and accurately.
Closely related to the initial quality of concrete pavement after construction is the means by which quality is controlled and ensured. In recent years, FHWA has emphasized developing performance specifications for concrete pavements. Performance specifications recognize the relationship between construction quality and long-term performance. By rationally controlling variables that impact long-term performance, the quality of the final product can be improved. Future research should identify the means of QC that require further study. In addition, the research should evaluate performance specifications, including warranties, for their benefits and limitations in the concrete pavement industry. Slow to gain acceptance, these alternative means for QC may prove beneficial to the industry in the long term.
The basic concrete pavement construction operations of today are not significantly different from those of 30 years ago. Concrete batching, transporting, placing, and curing are common elements of the construction process. Depending on the specifics of the project, other elements might include texturing and jointing. While the basic process has not changed, modest advancements have been made, including the use of technology to improve both efficiency and quality.
Future concrete pavement construction, however, should meet a growing set of user-driven demands. For construction, the most pertinent are the demands for quality and minimal delay. Sustainability is becoming a prevalent issue as well, leading to a need for its own unique set of solutions.
New equipment to permit operations such as one-pass paving will help meet these demands. One-pass paving is efficient while minimizing environmental impacts by incorporating 100 percent recycled materials into the process. Efficient NDT techniques also could be incorporated into one-pass paving operations to increase efficiency and ensure a high-quality product by automatically making necessary adjustments.
Because of increasing pressures for temporal and spatial limitations on construction, the concrete pavement construction community will require new construction techniques. Precast modular construction, for example, can be used to place a high-quality surface rapidly. While cost certainly will be a consideration, the mounting costs of traffic delays will justify the higher placement cost. Rapid-set, high-durability patching also will be required, including placement techniques that reduce the overall time for construction. Construction projects that generate no waste can be achieved only if researchers find ways to use in situ materials without jeopardizing long-term durability and performance. In short, the idea of night paving and daytime trafficking should be considered.
Although long-term concrete pavement performance issues are considered in detail in the next section, some construction-related issues are closely related to performance. For example, there is a demand for a better understanding of the required surface preparation for bonded, unbonded, and whitetopping concrete overlays. It has been demonstrated that the methods and quality of preparation of the existing pavement can significantly affect long-term performance, but guidance is needed in selecting optimum techniques. Attention should be given to the impact of surface preparation as it relates to other factors affecting long-term performance.
Concrete pavement texturing is another issue that warrants attention. Many techniques for concrete pavement surface texturing are in use today. Their pros and cons are still being determined, with debate among and within agencies about the performance of various techniques.
Another construction issue closely related to long-term concrete pavement performance is joint sealing techniques. For a given method, a number of construction techniques can be used. The impact of joint sealing on LTPP is an area that needs future research.
Research on improving the competitive nature of concrete paving in the highway industry is a construction-related issue that is sometimes overlooked. Two topics in particular are contractor training and alternative bidding procedures.
First, it has become increasingly difficult in recent years for contractors to hire and retain qualified labor. This applies to all levels of workers, from engineers to laborers. Additional research should be conducted to identify ways to rapidly and effectively train the concrete paving workforce. This training element is as important as any research and should be considered fundamental to research planning. The industry should remain competitive and viable.
A second topic worth considering is an investigation of alternative bidding procedures. Including elements other than cost into pavement bids could allow for contractor innovation. The resulting innovation could both improve the quality and lower the cost of the final product. As a result, concrete pavements would become more competitive in the highway industry.