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49  Conclusions Findings The data presented in Chapter 3 suggest the following general findings regarding the manner in which state DOTs consider, select, and use joint sealants: ⢠Many agencies believe there is a need for joint sealing, that joint sealants are an important element of concrete pavement performance, and that there are long-term benefits to pro- moting and carrying out quality joint sealant practices. ⢠There appears to be a benefit to documenting or monitoring measures to track the impact of sealant conditions on pavement performance, but survey results suggest that joint sealant condition is not well documented. ⢠There appears to be a need for tools or control protocols to facilitate agency inspection of cleaning and joint preparation operations. ⢠There also appears to be a need for aids and criteria for assessing the benefits of joint sealing, selecting joint sealant, or determining when to carry out resealing operations. ⢠The role of joint sealants has typically only been considered as a key item for ensuring pavement longevity. ⢠Not all agencies follow established practices regarding sealant shape factor and thus possibly risk premature bond failure. The lack of adherence to established guidance on SF limits seems to be driven by the notion that single sawcut joints can be adequately sealed at regular joint spacing intervals. This may be an area where sealant practices have evolved, yet practices regarding the associated joint spacing have not. The use of very narrow joints presents challenges to both joint preparation and sealing operations; neither can be carried out with any degree of confidence. For example, it is challenging to ensure the necessary cleanliness of narrow joints during inspection before installation. These factors, in combination with the higher stress levels, would likely result in early debonding and sealant failure. To maintain long-term performance of the joint sealant, DOTs may follow recommended joint design guidance and established joint preparation or joint inspection protocols. The interviewed DOTs benefited from carrying out and adhering to these guidelines. Other findings of note include the following: ⢠NDDOT has begun to establish a performance record for an alternative to traditional joint sealing (installed with the backer rod to give the seal the proper shape in the joint) by carrying out joint filling (installed without the backer rod, usually sealed to the full depth of the joint) instead. However, as reported in a number of previous studies, narrow and deep joint sealant configurations tend to lead to increased stress levels compared to conventional joint configurations (SF ⥠1, square or wide rectangle) under the same degree of deformation. C H A P T E R 5
50 Portland Cement Concrete Pavement Joint Sealant Practices and Performance Consequently, there is a possibility that the performance of filled joint sealant will still lead to erosion damage and faulting or other distresses caused by the debonding of the joint sealant. This also may not be true in all circumstances, which suggests the need for a more in-depth investigation as follow-up. ⢠There was no trend in the manner in which agencies prepare a joint for the installation of the sealant. Joint preparation is carried out according to agency-dictated methods and pro- cedures. Some states delegate joint preparation procedures and methods to the installation contractor. ⢠DOTs install joint sealants on the basis of their individual criteria, which likely results in different life spans for the same sealant types. This situation has been developing for some time but, because of the ambiguous standards used, does not appear to have produced clear results. It also has not resulted in the development of databases of any significant extent that can be used for analyzing the performance of joint sealants. ⢠Survey data and follow-up interviews of state agencies support the notion that the perfor- mance of joint sealants contributes significantly to the life of concrete pavements. ⢠The use of the national database related to joint sealants has benefited participating state agencies. Recommendations for Additional Research The results of this synthesis suggest several areas for further study. The reasons and objectives for such additional research are listed and elaborated here: ⢠In the design of the joint reservoir, the width of the joint tends to be narrower than the design guide of ACPA. With this trend, it may now be necessary to reassess sealant thicknesses that adhere to SFs proposed by ACPA in favor of narrow joint widths in order to adequately ensure the durability of the installation. Furthermore, the adequacy of current cleaning methods may also need reassessment. ⢠Some state agencies are moving away from the use of joint sealants. Closely related to this is a deficiency tied to the lack of data, tools, and resources to adequately make a material selection for a given candidate project for joint sealing. The decision for the need and type of sealants involved gets to the root of sealant requirements as far as their role in concrete pavement performance. Factors key to a decision of this type would be details related to the jointing system of the pavement, traffic levels, and type of subbase used below the concrete slab. In other words, a modeling tool is needed to ascertain the joint sealing performance and the risks involved with not sealing. ⢠Assessment of erosion potential will likely be key to the development of a tool to assess the need for sealing and the type of sealant that should be used for a given project. Such a tool would include factors such as traffic loading and frequency of loads, the existence of water and a pathway for the water to enter the sublayers (i.e., the effectiveness of the joint sealant), and the material properties of the subbase (Bakhsh, Zollinger, and Jung 2013). Therefore, assess- ment of erosion potential is key to relating sealant practices and effectiveness to pavement performance. ⢠It is recommended that a long-term investigation into the performance and condition of joint sealants be carried out toward the development of needed data, tools, and resources for agencies to make key decisions and use joint sealants in order to realize their full benefit.
