To seal or not to seal: the road to sustainability is oftentimes under construction

Scott Eilken

Co-Chair Seal/No Seal Group West Coxsackie, New York

he performance of concrete pavements is highly dependent upon the design, construction and maintenance activities. During the project development stage, owners select pavement design features based on their ability to balance cost and performance to establish what they believe is the best value or design optimization. The best value may be different than the lowest initial construction cost and can differ based on the category and function of the roadway. The expected level of performance depends, among other things, upon the desired level of service, facility type, traffic levels, speeds, etc. An urban freeway typically requires a higher performance level than a city street for example.

The owners of transportation facilities are faced with the challenge of balancing infrastructure needs with current and future budgets, designing for predicted future traffic levels, and procurement of construction contracts through a competitive low-bid system. Many of these aspects make selecting the best value difficult to say the least.

Today, economic pressures promote the use of least-cost construction techniques for new construction. Although at first blush these approaches may seem desirable, it is the long-term performance and true value of the design feature that should dictate their use. This is particularly true in markets where the construction commodities are escalating in cost at different inflation rates as has occurred in the U.S. for the last two decades.

However, oftentimes inadequate experience or data is available to properly quantify the benefit of a given design feature. A case in point is the use of joint sealants in concrete pavements. Since joint sealants can add as much as 10 to 12 percent to the initial construction cost, their value can only be determined if sufficient pavement life extension is derived as a result. However, this life extension has yet to be adequately defined. The use of joint sealants has been pervasive since the early 1900s and has been considered part and parcel with the construction of concrete pavements. In the early 1990s the value of joint sealing was challenged by the Wisconsin Department of Transportation and considerable differences in opinion have evolved since then. With the current economic times, it is even more difficult for owners to judiciously determine the true value of concrete joint sealants. A few examples follow which indicate the difficulty in making such a decision and why the road to sustainability is oftentimes under construction.

While constructing a four-lane roadway through an urban Joliet, Ill. area, diamond blade wet sawing was used to widen and wash the control joints prior to sealing. Sealant studies and research

The most recent FHWA Study, “Effectiveness of Sealing Transverse Contraction Joints in Concrete Pavements,” August 2008, indicated that little benefit was obtained through the use of sealed joints. However, the average age of the pavements investigated was less than ten years, so this study only evaluated the performance of early age concrete pavement. As mentioned, the value of any design feature must be determined from its impact on the long-term performance. The study results were further constrained in the fact that it dealt primarily with doweled pavements located in the wet freeze environment.

The current AASHTO Mechanistic Empirical Pavement Design Guide

The job in Joliet, Ill., involved sealing the transverse and longitudinal joints, including the curb joint, with hot pour sealant. Shown here is the hot pour sealing of the control joints on the test sections.

The joints in all sections are spaced at 15-foot intervals. The control joints are widened by diamond blade wet sawing and then washed.

(MEPDG) indicates a long-term benefit to pavement performance for joints sealed with compression seals after about 20 to 30 years in service. It does not indicate a benefit for pavements that are silicone sealed or sealed with hot pour. At this time it is not clear whether these two results conflict or differ only because the FHWA study was not able to evaluate pavements further into their service lives. However, the fact is that the current pavement design tool is indicating a benefit to sealed joints while the reported field evaluations are in conflict.

The recent SHRP 2 Renewal Research Report “Guidelines for the Preservation of High-Traffic-Volume Roadways,” 2011, indicated a five- to six-year pavement-life extension as a result of sealing concrete joints. This seemingly contradictory information between the various studies and practices exacerbates the problem for owners to make long-term performance decisions on the value of design features such as sealed joints.

Additionally, with the movement to reduce costs, narrower joint sealant applications are becoming more prevalent. The narrower joint widths are more difficult to clean and prepare and even more difficult to inspect. With agency downsizing becoming more common, it is doubtful that as intense inspection of construction products will continue. However, the proper installation of joint sealant is critical to its long-term performance.

The ACPA recently conducted a study entitled “Relative Cost of Concrete Highway Design Features,” 2010. One aspect of this study evaluated the costs of the various components comprising a joint sealant installation. The report indicated that the cleaning and preparation component comprised only 5 to 10 percent of the total sealant installation cost. However, the quality of this component of work may very well have the single greatest impact on sealant performance. Current trends would suggest that even greater emphasis should be placed upon proper preparation and installation practices and that this increased emphasis will have little impact on the overall costs.

New areas of concern

In recent times there has also been concern that anti-icing and deicing chemicals used by maintenance forces could impact concrete-pavement performance. Joint sealants appear to be one way to mitigate this effect. ASTM publication STP 1243 entitled “Rigid Pavement Joint Sealant Effectiveness in Reducing Chloride Intrusion” indicated that sealant effectiveness had an impact on measured intrusion levels. Although no unsealed joints were evaluated, sealant type indicated that there was an impact on chloride intrusion suggesting that better resistance to pavement deterioration was possible through sealed joints.

One aspect of joint sealant that has not traditionally been evaluated and is now quantifiable is the impact of unsealed joints on overall pavement noise. Joints do contribute to the overall tire-pavement noise levels and this can be as much as 5 dBA. Sealants can reduce the noise.

As evident from the preceding discussions, it is difficult for an owner to determine the true value of sealed joints. Further and significant research is still needed to answer this question once and for all. In the meantime, the consequences of ignoring the value of sealed joints may very well not show up until after 10 to 20 years creating problems for future generations.

Seal/No Seal Group

The Seal/No Seal Group was formed to respond to the age-old industry question about the value of sealing concrete pavement joints. Its mission is to develop a committed membership that takes responsibility for determining the longterm effectiveness of sealants in concrete pavements. To become involved, call CoChairs Scott Eilken at (708) 728-1895 or Charley Grady at (602) 524-1334, or send e-mail to info@sealnoseal.org. All are invited to join and participate in the research. Information on the Seal/No Seal Group and their efforts can be found at www.sealnoseal.org.