Today, 96% of the state agencies building and maintaining concrete roadways, and all agencies building and maintaining concrete airport pavements, require joint sealing for new pavements. Many advancements have been made in joint sealant materials. A valid question within the industry regards how well sealants work to improve pavement performance. That question remains largely unanswered and is the crux of the issue of whether to seal or not seal concrete pavement joints. Research has been proposed to give insight and provide answers.
As joint sealants have evolved from simple heated-tar materials to complex, engineered materials, concrete pavements have evolved as well. Now, transverse joints in new concrete highways almost always contain dowels to facilitate load transfer across the joint. In the past 25 years, the average joint spacing used by state agencies has changed to 15-20 ft from 20-100 ft. At the same time, base materials used in many states have changed from relatively impermeable, granular materials to permeable materials that carry water to an edge drain system.
Some design changes, such as the widespread use doweled joints, have had a dramatic influence on the performance of concrete pavement for heavy truck traffic. Yet, there is no scientific link to establish the impact of some of the other new pavement features. For instance, it is too soon to quantify whether permeable base materials will actually improve performance cost effectively over a 25-40 year pavement life-span. In a similar fashion, modern sealant materials suffer from the missing link to performance.
The missing link lies in the research. For years, research associated with sealant technology has been predicated upon the assumption that sealants contribute to pavement performance. Unfortunately, this assumption has directed research in a way that has left very little tangible evidence of the impact of sealants on overall pavement performance. Similarly, much of the evolutionary work with sealants was made on older pavement designs and with older sealing materials.
Wisconsin Department of Transportation is the only agency to provide comprehensive information on the impact of sealing to overall performance. Their officials conclude that sealing transverse doweled joints provides no significant benefit in Wisconsin. Although their conclusions are intriguing to some, it is unknown if these conclusions are valid elsewhere. In order to study the issue objectively, their original research needs to be expanded to a national scale to quantify differences across various climatic conditions, soil conditions, concrete designs, pavement designs, applications, modern sealing materials, etc.
These and a range of other factors must be studied, not simply debated, and will necessitate a commitment to field research to understand both sides of the issue. Research need statements have been prepared by the Innovative Pavement Research Foundation and the Transportation Research Board's Committee A3C13 "Sealants and Fillers for Joints and Cracks." Each seeks the answer to the question: "How does sealing transverse contraction joints influence the overall performance of concrete highway pavements?"
State Departments of Transportation are also getting into the act of placing "no seal" test sites. Many are simply ommitting sealant from portions of a project. These sections are candidates for the comprehensive study. After sufficient time and examination, the results will establish the link between sealing joints using modern materials and pavement performance.
Improvements to jointing materials and their application are likely to arise from studying the interaction between joint design and overall pavement performance. Perhaps new research will once again change the expectations that pavement engineers place on joint sealing materials for new concrete pavements. In the meantime, it appears that the current practice of sealing transverse joints with either hot-pour, silicone or compression seals will remain unchanged by most state agencies across the country. Similarly, until sound national research proves otherwise, it is likely that agencies will, as a part of pavement rehabilitation programs, continue to reseal joints whose materials have deteriorated over time.
