Portland Cement Concrete Pavement Joint Sealant Practices and Performance (2021)

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6 Literature Review This chapter documents the results of the literature review conducted before the distribution of the questionnaire. The topics discussed in this chapter include the following: • Joints in concrete pavements • Early use of sealant in PCC pavements • Current sealant material types • Current sealant practice • Joint and reservoir design (including sealant movement and geometry, surface configuration, and material selection) • Construction and installation • Joint sealant performance • Maintenance (resealing) • Alternative methods Joints in Concrete Pavements Joints in concrete pavements are primarily intended to provide freedom of movement of a slab relative to volumetric changes in the concrete due to drying shrinkage, temperature changes, and moisture variations. Functionally speaking, joints are designed to control cracking and minimize stresses in the pavement caused by these changes, but joints should be sealed to limit or prevent moisture infiltration or the entry of incompressible materials. The placing of joints at regular intervals has been validated by experience but has evolved over time. The first specifications regarding the placement of joints in concrete pavements were addressed in guidelines for transverse joint spacing by the American Concrete Institute in 1914 (Hall et al. 2008). Discontinuities presented by the use of joints in PCC pavements (Shober 1996) have been a major performance concern because they tend to create planes of weakness in the slab. In many instances, distresses often initiate and propagate at or near these joint locations. Therefore, attempts have been made to reduce the number of joints by extending joint spacing, but these measures tend to be offset by the effect of the sensitivity of the concrete to temperature- or moisture-induced deformations in a slab. The use of customized curing techniques and construction methods has perhaps had some success in yielding PCC pavements with longer joint spacing. Nonetheless, field observations related to the improvement of joint patterns have been suggested to help avoid early distresses at joints (Ioannides, Long, and Minkarah 2004). Early Use of Sealant in PCC Pavements In 1871, a U.S. patent represented the use of gum, tar, or rubber materials as joint filler in concrete joints (Teller and Sutherland 1936). Later, it was common construction practice to use C H A P T E R 2

Literature Review 7   bituminous materials to fill the joints. Bituminous materials were relatively low-cost and easy to place. In 1912, the first reinforced concrete pavement was constructed in Port Huron, Michigan. Expansion joints in this project extended through the entire slab thickness, and asphalt cement was used to fill the joints and prevent the infiltration of water (Hall et al. 2008). As early as 1910, concrete pavement maintenance efforts included the sealing of any slab cracks, mostly with sealant material that was a mixture of sand and tar (Hall et al. 2008). In the early 1920s, many states studied various tar and asphaltic filler materials for repairing cracks in concrete pavements. One of these studies was sponsored by the Iowa State Highway Commission in 1923 to identify grades of tars and asphalts suitable for use in crack mainte- nance. In the experimental sections located outside of Des Moines, Iowa, different materials were tested, including three types of tars, nine asphalts, blown oils, an emulsified bitumen, and a single light-colored material (Hall et al. 2008). The cracks were pressure-cleaned and dried before the installation of the filler material. After the final inspection, all three grades of tar were nearly 100 percent intact, adhering to the wall of the joint reservoir; these were the only materials exhibiting excellent performance. Current Sealant Material Types Today, there are primarily three types of sealants used for rigid pavement applications: asphalt-based sealants, silicone-based sealants, and compression sealants. Historically, the most commonly used sealant materials for concrete pavement joints have been hot-pour asphalt-based materials. However, silicone-based sealants [ASTM (American Society for Testing and Materials) D5893] and preformed compression sealing materials (ASTM D2628) have become more suitable for use in rigid pavements and have become the preferred alternative of many state DOTs (Lynch et al. 2000). Hot-pour sealants—Hot-pour sealants were the first type of sealant developed. Manufacturers have improved the adhesive qualities of these sealants while maintaining their excellent exten- sibility and low modulus (ACPA 2018). For proper installation, the materials require heating, usually between 350°F and 400°F (177°C and 204°C). The contractor must ensure that the sealant is installed at the required temperature. Silicone sealants—Silicone sealants are polymer, field-poured liquids. Pavement specifi- cations started including these products in the 1970s (Zimmer, Carpenter, and Darter 1984). Installation procedures are similar to those for other formed-in-place sealants. Silicone sealants consist of self-leveling (ultra-low modulus) and non-sag (low modulus) types. Self-leveling silicones flow into shape once injected into the joint reservoir, typically without finishing or tooling; installing non-sag silicones requires tooling. The material comes prepackaged for immediate application; however, silicone materials must be properly stored. Manufacturers recommend storing containers out of direct sunlight and at humidity below 80 percent and temperatures between 35°F and 90°F (2°C and 32°C) before use. A silicone sealant is also a single component that does not require mixing or heating for installation. However, because moisture suspended in the surrounding air facilitates the curing of silicone sealant, manufacturers caution against placing silicone sealant during rain events or when the concrete is below the dew point temperature. Silicone sealants maintain elastic behavior in climates with a broad temperature range. Most silicones develop a low elastic modulus, allowing good extension and compression recovery. Typical low-modulus silicones can undergo, without consideration of bonding capacity, at least 100 percent extension and 50 percent compression without detrimental effects (ACPA 2018).

8 Portland Cement Concrete Pavement Joint Sealant Practices and Performance Preformed (compressive) sealant—Manufacturers introduced preformed compression sealants in the early 1960s. They differ from other sealants because they are ready for applica- tion without field heating, mixing, or curing. Unlike formed-in-place sealants that undergo compression and stress, preformed compression sealants are designed for compression only after deployment. Therefore, their effectiveness depends solely on the lateral pressure over their lifespan (ACPA 2018; Bakhsh and Zollinger 2015; FHWA 2019). Neoprene, synthetic rubber manifesting excellent compressed rebound stiffness, is the main compound in preformed sealants. These sealants consist of webs that provide the internal force against the reservoir walls to hold them in place. Manufacturers provide these sealants with different nominal widths and depths to fit different reservoir dimensions. In all cases, the sealant width must exceed the maximum (coldest weather) joint reservoir width. Generally, preformed sealants should be twice the width of the reservoir, but the sealant and the reservoir widths should be carefully selected together to ensure compatibility. In addition, the reservoir depth must exceed the sealing depth during compression. Good performance results when preformed sealants stay compressed 20 percent to 50 percent over a range of joint openings (ACPA 2018; Taylor et al. 2012). Current Sealant Practice In recent years, states have adopted a greater variety of joint sealing practices for jointed pavements, according to local preferences, climate, and traffic conditions. The driving force behind these variations may in part be a perception that sealing costs can be decreased without sacrificing performance. Generally, where good drainage exists in the sublayers or where climates are very hot and dry, joints experience a lower degree of distress because they likely hold less moisture. This may lead to attempts by some agencies to get by with narrower sawcuts and no sealing, whereas agencies in wet climates and with less drainable subgrade materials prefer to have sealed joints (Morian and Stoffels 1998). Transverse contraction joints in PCC pavements are traditionally constructed in the following steps: 1. Making an initial sawcut to control cracking 2. Making a second sawcut to create a joint sealant reservoir 3. Cleaning and preparing the reservoir faces 4. After a sufficient amount of drying, placing a backer rod in the reservoir to keep the sealant from adhering to the bottom of the reservoir and to create a curved bottom surface for the sealant 5. Placing sealant material in the reservoir (which may include tooling the sealant into place) Joint and Reservoir Design This section reviews factors related to the design of a joint sealant, as reported in the literature, including sealant movement and geometry. As noted earlier, one purpose for joints in concrete pavement is to control cracking and to provide movement for concrete expansion and contraction caused by temperature and moisture changes. Sealed joints typically limit the infiltration of water into the joint and the underlying pavement substructure. Joint seals may also limit the infiltration and accumulation of fine, incompressible material on the joint face. Unless otherwise noted, the subsequent discussion considers various concrete pavement joints collectively. The components of a sealed joint, illustrated in cross-section in Figure 1, are the sealant (i.e., joint material), the reservoir (i.e., the joint well or cavity containing the sealant), and the backer rod (a compressible material that fits into the joint reservoir). The backer rod

Literature Review 9   helps to establish a suitable sealant shape factor (SF). The SF is the ratio of the sealant depth to its width and is useful to minimize stresses within the sealant and consequently prevent three- sided adhesion. Reservoir Size and Joint Movement Reservoir size is an important consideration to facilitate the proper installation and function- ing of a sealant. The reservoir should be wide enough to facilitate proper cleaning of the sawcut surface to enhance adhesion between the sidewalls of the joint well and the sealant (ACPA 2018). A sealant must be capable of accommodating the anticipated joint opening and closing due to temperature changes. Joint movement estimates have typically been made using the following equation: ΔL = C • L(αΔT + ε), where ΔL = Expected change in slab length; in. (mm); C = Base/slab frictional restraint factor (stabilized material: 0.65, granular material: 0.80); L = Slab length; in. (mm); α = PCC coefficient of thermal expansion; × 10–6/°F (× 10-6/°C); ΔT = Maximum temperature range; °F (°C); and ε = Shrinkage coefficient of the concrete; in./in. (mm/mm). Because the width of the joint sealant varies according to the temperature-induced movements, a suitable reservoir size should be selected to accommodate the movement between adjacent slabs to stay within allowable strain limits. At the same time, material and climatic variability should be accounted for to avoid overextension and damage to the sealant. Variability can be addressed using probabilistic models to estimate a range of movements for a given combination of concrete materials and joint spacing (Lee and Stoffels 2003). Maximum Allowable Strain Different sealant types can withstand different levels of strain as a function of their bonding capability. The maximum allowable strain at the extreme sealant fiber depends on the amount of sealant elongation (joint opening) and the SF (Figure 2). Most hot-pour liquids can withstand Figure 1. Examples of preformed seals, formed-in-place seals, and joint fillers (ACPA 2018).

10 Portland Cement Concrete Pavement Joint Sealant Practices and Performance about 20 percent tensile strain of their initial width. Silicones and some other low-modulus materials can theoretically undergo up to 100 percent strain. However, manufacturers recommend using total strains of no more than 50 percent and ideally only 25 percent for design (ACPA 1995) in order to limit debonding potential. In previous studies (Khuri 1991, 1993; Khuri and Tons 1992), stress and strain analysis of a joint sealant concluded that the strain levels of joint seals should be limited from 25 percent to 50 percent. But it appears that these limits are largely empirical and lack theoretical justification. It appears that much of the sealant research in the past was focused mainly on internal stress levels and less on the tendency for debonding between the sealant and the wall of the joint reservoir. What has been lacking is the consideration of the effect of the internal stress and strain analysis and the associated boundary conditions on the bond stress at the sealant- concrete interface. Sealant Geometry A reasonable engineering approach to represent sealant behavior is to account for the effects of joint width, depth, and curvature on critical strain levels. Tons’s research on cell design led to identifying the significance of “shape factors (SF) (defined as Width/Depth)” on sealant behavior (Tons 1959). SF has been shown repeatedly to be a significant factor in engineering practice for the design of joint sealants (Tons 1959, 1965; Khuri 1991, 1993). Earlier studies (Catsiff, Hoffman, and Kowalewski 1970a, 1970b; Catsiff 1971) of sealant stress-strain behavior used the finite element method, the first use of this method of analysis to examine the distribution of stress in a joint sealant with a rectangular cross-section. Unfortu- nately, this study did not make a comparison to other cross-sections associated with an hourglass shape. Another study involving laboratory static and cyclic testing of joint sealants conducted by Myers (1990) examined the effect of joint shape on sealant performance and stress distribution within the sealant. This research included various joint shapes in the analyses; however, the study did not address the effect of the hourglass shape in laboratory testing because the focus Figure 2. The horizontal strain in the sealant for different shape factors (Bugler 1998).

Literature Review 11   at the time was on fillet joints. Moreover, in this study, cyclic testing did not produce definitive results because of the limited range of strains tested. Nonetheless, the results of this study show, somewhat surprisingly, that the peak stress of the hourglass joint is only about one-third of the stress in a square joint, which indicates the importance of sealant shape. A recent study (Kim and Zollinger 2020) also investigated the distribution of stress in both the sealant and the joint well–sealant interface. The study also included the effect of sealant geometry (SF) as well as a new parameter referred to as the degree of curvature (DoC). This study suggests that, as the values of SF and DoC increase, the stress throughout the section and stress concentrations along the interface decrease, which serves to limit premature adhesive failure (Kim and Zollinger 2020). Figure 3 shows a typical sealant configuration illustrating the dimensions associated with the SF, which has been noted as being critical to the long-term success of poured sealants. An SF equal to or greater than 1 induces lower stresses in a joint sealant than an SF less than 1. The lower or reduced internal stresses minimize adhesive or cohesive debonding as a result of the use of proper SFs (ACPA 2018). Table 1 lists reservoir and sealant dimension recommendations for hot-pour and silicone sealants. For hot-pour materials, filling the reservoir flush with the pavement surface is preferred Hot-pour sealant Silicone sealant R = 0 in. (0 mm) Flush Fill; No Recess B = Depth to Top of Backer Rod = Min. of 5/8 in. D = Nominal Sealant Thickness (Depth) = Min. 1/2 in. W = Joint Reservoir and Sealant Width = Min. 1/4 in. Shape Factor (W/D) = 1/1 R= Sealant Recess 1/4 to 3/8 in. (6 to 10 mm) B = Depth to Top of Backer Rod = Min. of 5/8 in. D = Nominal Sealant Thickness (Depth) = Min. 1/4 in. W = Joint Reservoir and Sealant Width = Min. 1/4 in. Shape Factor (W/D) = 1/1 to Max. 2/1 Table 1. Typical reservoir dimensions (ACPA 2018). Figure 3. Typical reservoir configuration for liquid sealant (B = depth to top of backer rod; D = nominal sealant thickness; R = sealant recess; W = joint reservoir and sealant width).

12 Portland Cement Concrete Pavement Joint Sealant Practices and Performance because experience suggests that tire contact with the sealant keeps it pliable and reduces joint noise. For silicone sealants, SF design inherently includes recessing the sealant below the pave- ment surface by 1⁄4 to 3⁄8 in. (6 to 10 mm) to prevent tire contact. The SF recommendations of 1 to 2 for a silicone sealant and 1 for a hot-pour sealant were based only upon the material cross-section itself rather than the associated bond conditions (ACPA 2018). The effect of using a narrow joint configuration is largely unknown; however, it appears that optimization of the SF relative to the type of material and the degree of bond at the sealant–joint reservoir interface should enhance sealant performance. The South Dakota DOT (SDDOT) conducted a study to investigate silicone sealant adhesion failures. The study concludes that surface moisture on the interface between the silicone and the concrete was compounded by improper control of the installation process (i.e., thicker cross- section), which resulted in either increased stress or reduced bond strength on the interface between the sealant and the wall of the joint reservoir. This assertion was validated through field surveys and the analysis of lab experimental data (SDDOT 1994). In 1991, Arizona DOT (ADOT) built a test pavement segment on eastbound US-60 in Mesa, Arizona, to evaluate the effect of transverse and longitudinal joint sealing on pavement per- formance in jointed plain concrete pavement (JPCP) (Smith et al. 1999). The latest evaluation included a detailed visual inspection to identify sealant failures. The report showed that most joint sealants maintained a bonded length for 15 years without distress (Hall 2009). Surface Configuration for Joint Sealing Sealants are placed in the joint in several different configurations, as shown in Figure 4 (Smith et al. 2014). These configurations are described here: • Most silicone sealants are placed in a recessed configuration with the top of the sealant in the reservoir roughly 0.12 in. to 0.25 in. below the pavement surface. This configuration prevents the sealant from being removed under high-traffic conditions. Consequently, silicone sealants should be placed only in the recessed configuration. • Flush-filled configurations apply only to hot-pour sealants placed even with the pavement surface. Some manufacturers recommend this configuration because it eliminates a place for incompressible materials to collect and helps the sealant remain more ductile as it is subjected to the kneading action of passing tires (Smith et al. 2014). • Overband configurations involve overfilling the reservoir slightly above the pavement surface. Although this method maximizes the bonding surface area between the sealant and pavement, it is susceptible to snowplow damage and can negatively affect ride quality (Evans, Smith, and Romine 1999). Therefore, it is not recommended for most joint sealing applications. Figure 4. Sealant surface configurations (Smith et al. 2014).

Literature Review 13   Material Selection When planning a joint sealing project, one of the primary design activities is the selection of appropriate sealant material. Material selection is dependent on a number of factors, typically including the following: • Climate conditions (at the time of installation and during the life of the sealant) • Joint/crack characteristics and spacing/density • Traffic level and percentage of trucks in the traffic mix • Material availability and cost The preceding list includes factors that govern the range of movement that the joints or cracks, and the sealant installed in them, will experience. Because sealant materials have different extension properties, the sealant material selected must be able to accommodate the maximum anticipated joint opening. The American Concrete Pavement Association (ACPA) offers a tool (see http://www.apps.acpa.org/apps/JointMovement.aspx) for estimating joint movement and sealant elongation; this tool can be used to assist in the material selection process (ACPA 2018). Other factors discussed next include different types of materials that are typically used as joint sealants, more critical performance-related material properties, and cost considerations that may affect the selection of a sealant material. Selecting Sealant Materials Many factors should be considered when selecting a suitable joint sealant material, including the type of joint and expected joint movements, climate (which affects required extensibility), bond compatibility with substrate materials (e.g., concrete only or concrete and asphalt), chemical compatibility with substrate material (e.g., the sensitivity of some silicone sealants to limestone aggregate), need for rapid sealant curing, material and installation costs, and expected performance life (FHWA 2019). Silicone and preformed compression sealants typically out- perform asphalt-based sealants for concrete pavements but are also proportionally more expensive. The use of longer-life sealants should be considered, even with added initial costs, because joint sealant maintenance is often deferred (or ignored) (FHWA 2019). Once a sealant material is selected, an appropriate reservoir design should be developed for optimum performance of the sealant material. For formed-in-place sealants, this decision may also involve the selection of a backer material (as appropriate, depending on the type of application) to prevent the sealant from displacing into the joint. Furthermore, the initial material selection may consider the following: • Joint movement behavior, which can be estimated on the basis of a combination of climate and joint spacing. Conservatively estimating joint movement is important, because a study of silicone and polyurethane seals in full-scale test sections by the Michigan DOT indicates peak movements of 0.16 in. (4 mm) after initially estimating joint movement to be 0.065 in. (1.7 mm) (Eacker and Bennett 2000). • Traffic volume and traffic characterization may also come into play. For instance, the Wisconsin DOT (WisDOT) has observed that higher vehicle speeds may prevent incom- pressible materials from lodging in joints (Shober 1996). • Life-cycle cost analysis should be conducted to assess the costs of initial sealing and resealing over the sealant life. In general, hot-pour sealants provide 3 to 8 years of service life after installation, silicone sealants provide 8 to 15 years of life, and preformed seals may provide up to 20 years of service (Brown 1991; Lynch, Chehovits, and Luders 2002; Bakhsh, Zollinger,

14 Portland Cement Concrete Pavement Joint Sealant Practices and Performance and Jung 2013). However, preformed seals are the most expensive and hot-pour sealants the least expensive, so these costs and expected service lives could be considered in the selection process along with other factors. Other Performance Requirements When selecting a suitable joint sealing product for a paving project, there are a number of relevant sealant properties to consider, including the following (ACPA 1995, 2018): • The elasticity and modulus of a sealant, which describes its deformability under load. This parameter is a compromise between two desired properties: the material should be adequately deformable at low temperatures to displace with the faces of contracting slabs, yet it should not be excessively soft at warm temperatures so that it flows out of the joint or is damaged by incompressible materials. • The durability of a sealant, which describes its resistance to deterioration or aging over time due to environmental and traffic effects. In addition to these general material property factors, there are specific properties to be considered for formed-in-place sealants (ACPA 1995, 2018): • The adhesion and cohesion of formed-in-place sealants describe their ability to (a) adhere to the sides of the joint and (b) cohere under load (resist failure within the seal itself). • Non-sag formed-in-place sealants require manual tooling to push the material against the sidewalls to promote adhesion and shaping. Self-leveling formed-in-place sealants naturally flow into the reservoir and adhere to the faces of the joint, but tooling will help promote cohe- sion to the joint well walls. • Formed-in-place sealants may be selected with a compatible backer rod. If used, a backer rod must be sufficiently compressible to remain at the prescribed installation depth. • Climate conditions at the time of installation can affect sealant performance. Table 2 provides a summary of common sealant materials, material specifications, and descriptions. Selecting Backer Rod Materials A backer rod is typically inserted in PCC joints before sealing to properly shape the sealant and keep it from settling into the reservoir. It also prevents the sealant from bonding to the reservoir bottom and, if properly selected and installed, helps maintain the proper sealant thickness. The backer rod material must be flexible, compressible, nonshrinking, nonreactive, and nonabsorptive. A shrinking backer rod material may allow the sealant to flow past the backer rod before the sealant sets. A backer rod’s material should also not react with the sealant material because doing so could produce bubbles in or stain the sealant. Finally, the backer rod material should not absorb water or bond to the sealant because that could shorten the sealant’s performance life. Several types of backer rods are described in Table 3 (Evans, Smith, and Romine 1999). Each type has specific properties and intended uses. For example, some types of backer rods are designed to withstand the extreme temperatures of hot-applied sealants, whereas others are intended only for cold-applied sealants. Softer, extruded foam rods were developed with irregular edges to better seal joints. When a shallow joint well is involved, backer tapes have also been used. Manufacturers’ recommen- dations should be followed when selecting backer rod type because sealant and backer rod materials must be compatible. The more commonly used backer rod materials for hot-applied sealants are cross-linked extruded foam rods. Typically, an extruded closed-cell polyethylene

Literature Review 15   Category Material Type Specification(s) Description Liquid, Hot-Applied Sealants (Thermoplastic) Polymerized/ Rubberized Asphalts ASTM D6690, Type I Moderate climates, 50% extension at 0˚F (–18˚C) ASTM D6690, Type II Most climates, 50% extension at –20˚F (–29˚C) ASTM D6690, Type III Most climates, 50% extension at –20˚F (–29˚C) with other special tests ASTM D6690, Type IV Very cold climates, 200% extension at –20˚F (–29˚C) Liquid, Cold/Ambient- Applied Sealants (Thermosetting) Single-Component Silicone ASTM D5893, Type NS Non-sag, low modulus ASTM D5893, Type SL Self-leveling, no tooling, low modulus Two-Component Elastometric Polymer (polysulfides, polyurethanes) Fed Spec SS-S- 200E, Type M Jet-fuel resistant, jet-blast resistant, machine-applied fast cure Fed Spec SS-S- 200E, Type H Jet-fuel resistant, jet-blast resistant, hand-mixed retarded-cure Solid, Cold/Ambient- Applied Sealants Polychloroprene Elastomeric (Neoprene) ASTM D2628 Jet-fuel–resistant preformed compression seal Lubricant ASTM D2835 Used in installation of preformed compression seal Expansion Joint Filler Preformed Filler Material ASTM D1751 Bituminous, nonextruding, resilient ASTM D1752, Types I–IV Sponge rubber, cork, and recycled PVC (polyvinyl chloride) ASTM D994 Bituminous Table 2. Types of joint sealants and related specifications (Smith et al. 2014). Backer Material Type Applicable Standard Properties Compatibility Extruded Closed-Cell Polyethylene ASTM D5249, Type 3 NMA, ECI, NS Most cold-applied sealants Cross-Linked, Extruded Closed-Cell Polyethylene ASTM D5249, Type 1 HR, NMA, ECI, NS Most hot- and cold- applied sealants Extruded Polyolefin ASTM D5249, Type 3 NMA, NS, NG, CI, IJ Most cold-applied sealants NOTE: NMA = non-moisture absorbing; ECI = essentially chemically inert; NS = non-staining; HR = heat resistant; NG = non-gassing; CI = chemically inert; IJ = fills irregular joints reservoir. Table 3. Backer rod materials (Evans, Smith, and Romine 1999).

16 Portland Cement Concrete Pavement Joint Sealant Practices and Performance foam or extruded polyolefin foam rod is used for cold-applied sealants. The diameter of the rod should be at least 25 percent larger than the width of the joint. The backer rod is available in diameters between 10 mm and 75 mm, or wider. Because joint widths can vary in a rehabilitation project, enough rod sizes must be available to achieve a tight seal in all joints. Construction and Installation Installation and cleaning procedures are outlined here. Joint Preparation Method and Procedure Transverse contraction and longitudinal joints should be sawed in two phases. The initial sawing is designed to initiate cracking at a desired joint location. It should be made with a 1⁄8-in.-wide blade at the required depth. The second sawing provides the proper joint well dimensions to accommodate the SF required for the sealing material used (FHWA 2019). The joint well reservoir that will contain the joint sealant is formed through initial or secondary sawcutting. Traditionally, joint seals are installed in the reservoirs created by a secondary saw- cutting operation that produces a wider joint to accommodate the appropriate sealant SF. This secondary sawcut can be made as part of the initial sawcutting or performed as a separate opera- tion. Some important considerations for the initial or secondary sawcutting are the following: • The sawcutting must produce a reservoir with sufficient depth for the designed reservoir shape, backer rod, and additional room required to recess the sealant to a certain depth within the reservoir. • A watery mix used to cool the cutting blade can leave a heavy residue on the face of the joint and significantly decrease the bond strength between the sealant material and the joint (Bakhsh and Zollinger 2015). The newly cut reservoir should be cleaned immediately after sawing, regardless of sealant installation plans (FHWA 2019). Plans to seal joints for a given concrete paving project do not affect conventional joint sawing practices for contraction joints. Joint fillers can be installed directly into the original (unwidened) sawcut (ACPA 2010). However, a second sawcut may still be used to create a reservoir for the filler material. In this case, although a formal joint SF is typically not adopted, joint movements must be extremely limited or debonding will result because of the high state of stress that infilled joint configurations undergo. Before sealant installation, the reservoir should be cleaned to remove debris and dust from the reservoir walls. This can be done in a number of ways, including air blasting, sandblasting, and water-blasting, as specified by the sealant manufacturer or highway agency (ACPA 2010). When using air blasting, it is important that the air stream is free of lubricants, because any oil film on the faces of the reservoir can interfere with proper adhesion (ISU 2004). For similar reasons, the joint sidewalls should be allowed to dry sufficiently after water-blasting, because moisture can limit the adhesion of formed-in-place sealants. Immediately after cleaning, the backer rod, if required, should be installed. The backer rod diameter should fit snugly to prevent the backer rod from displacement during installation. Considerations in the installation of backer rods are described here: • The backer rod should be compressed into the reservoir at the depth that provides the designed sealant shape. The backer rod is typically pressed into the reservoir with a roller device. • Sufficient backer rod material should be available for installation over the entire length of the joint in a relaxed state. The backer rod should not be stretched more than about 5 percent of its length.

Literature Review 17   • The backer rod used with hot-pour sealants should tolerate the specified application temper- ature of the sealant. ACPA (2018) notes that, although heat-tolerant open-cell backer rod products may not melt on contact with hot-pour sealants, these open-cell products can retain moisture in a way that contributes to detrimental performance. As mentioned previously, although it is not recommended, some agencies may elect to forgo the backer rod and fill the entire reservoir cavity with a hot-pour sealant (Taylor et al. 2012). Regardless, the sealant should be installed as soon as possible after reservoir preparation. The finished reservoir should be clean and dry. Methods to accelerate drying should consider that the concrete at the joint is hydrating. Thus, compressed air is acceptable, whereas the use of a blow torch is not. Inspection Method and Joint Preparation Adhesion loss is the most common distress occurring in joint sealants (Taylor et al. 2012; Bakhsh and Zollinger 2015). In order for sealant geometry to make any difference in performance, the sealant must be fully bonded to the wall of the joint reservoir, which is typically where failure occurs in a joint sealant system. Furthermore, if the boundary conditions are considered, the contact interface between the sealant and the joint well wall is where the most critical stresses occur. Even though several studies have addressed a series of standardized tests relative to load level and sealant thickness (Malla et al. 2007; Malla, Swanson, and Shaw 2011; Li et al. 2014; Kim and Zollinger 2020), no manufacturer lists bond strength as a specification for its product. In order to ensure sealant performance, establishing standards for sealant adhesion strength may be necessary. Cleaning and Drying the Joint A key to the successful performance of a joint sealant is to effectively inspect the reservoir cut faces before carrying out installation operations. Previous research has indicated that the lack of cleaning is a major problem affecting sealant bonds. Appropriate emphasis on quality assurance and inspection can perhaps maximize sealant bond strength and greatly improve not only joint sealant but also concrete pavement performance life (Lynch 1989; Bakhsh and Zollinger 2015; ACPA 2018; Kim and Zollinger 2020). SDDOT reported that, between 1984 and 1990, a Sioux Falls test pavement experienced wide- spread adhesion failures, evidenced by pumping from the joints during and after rain events. The study was conducted to identify the adhesion failure mechanism manifest in silicone joint sealants and to recommend appropriate changes to ensure acceptable sealant performance. The report concluded that high-moisture conditions on the concrete reservoir walls were probably present during the installation of the silicone sealants, resulting in a high degree of adhesion failure as verified from field surveys and analysis of laboratory experimental data (SDDOT 1994). Reservoir wall faces require thorough cleaning and drying to ensure sealant adhesion and long-term performance. Proper cleaning requires mechanical action (such as sandblasting) and pure water flushing to remove contaminants. The following outlines the recommended procedures (ACPA 2018): • Step 1. Sawcut widening—Sawing/widening shapes the reservoir for sealant installation. The reservoir sawcut will remove any raveling caused by the initial cut and provide the proper dimensions for the sealant. • Step 2. Cleaning—Cleaning is the most important aspect of joint sealing. For all formed-in- place sealants, manufacturers suggest similar cleaning procedures. Likewise, the performance of formed-in-place sealant products is predicated on preparation and cleaning procedures.

18 Portland Cement Concrete Pavement Joint Sealant Practices and Performance • Step 3. Backer rod installation—The backer rod should be compatible with the sealant and sized about 25 percent to 50 percent greater than the reservoir width. A backer rod is inserted easily with a double-wheeled steel roller that will force it uniformly to the proper depth (Figure 5). • Step 4. Cleanliness check—The installation of sealant should not proceed until the reservoir walls are free from dirt and dust. • Step 5. Sealant installation—Installation requirements vary slightly for each sealant type. Manufacturers recommend some curing or cooling time for formed-in-place sealant materials and typically suggest limits on air and pavement temperatures for installation. Cleanliness Check There are various ways that joint reservoirs can be assessed for cleanliness: • Visual inspection—The inspector visually inspects the reservoir for proper cleanliness. • Finger test—With a finger and cloth, an inspector can simply wipe the reservoir sidewalls to check for any traces of dirt and dust. However, this method is feasible only for wider joint reservoirs. • Wipe test—This is a test procedure developed by Wiss, Janney, Elstner Associates and adopted by ACPA as a standard quality control test. The wipe test captures the relative amount of concrete dust, slurry, and contaminants on the reservoir walls. The procedure requires using a clean black cloth to wipe the surface of the joint to determine the presence of contaminants. It is important that the inspector handle the cloth carefully to avoid contaminating it with debris from the surface (WJE 2013). Moisture Check The bond strength of the joint sealant to the wall of the joint reservoir is a function to some extent of its moisture content. However, direct measurement of the moisture content of the surface concrete under field conditions is complicated (Li et al. 2014; Joshaghani and Zollinger 2017). Figure 6 shows laboratory measurements of the moisture content of the bonding concrete surface relative to measured sealant bond strengths. Clearly, if the moisture content is high enough, it can reduce the strength of the bond even if the joint is clean. The level of moisture content can possibly be measured indirectly by measuring the conductivity of the surface concrete using equipment such as a percometer (Kim, Bhardwaj, and Zollinger 2018). The current method of joint reservoir moisture detection is by visual Figure 5. Double-wheeled backer rod roller (ACPA 2018).

Literature Review 19   inspection. General quality control tests for joint reservoir moisture conditions are currently in development (ACPA 2018). Sealant Installation For each type of sealant, installation specifications are slightly different. Manufacturers recom- mend some curing time for most liquid sealants before opening the pavement to traffic. Many manufacturers of liquid seals often set restrictions on ambient and pavement temperatures for installation. Compression seal manufacturers specify the desired limits on the amount of stretching allowed during installation. Hot-pour sealants—The installation of hot-pour sealants requires heating to temperatures of 350°F (177°C) and higher before application (ACPA 2018). Because of these extreme tempera- tures, the rapid cooling of the hot-pour sealant during application should be avoided, and it is recommended that the installation should be conducted at a minimum ambient temperature of 40°F (4°C) (FHWA 2002). At the same time, the sealant should not be overheated because doing so can adversely affect sealant performance. The manufacturer’s recommendations should be consulted for the proper heating and thermal management of the sealant. The hot-pour sealant is typically placed into the reservoir using a wand (see left image of Figure 7). The sealant should fill the reservoir uniformly, and the reservoir should be filled from the bottom up to avoid trapping air bubbles. Because hot-pour materials are self-leveling, no additional installation effort is required beyond filling the reservoir to the desired level. Silicone sealants—Like hot-pour sealants, silicone sealants are caulked into the reservoir in a bottom-up manner in order to limit trapped air. Silicone sealants are available as self-leveling and non-self-leveling products: • The most popular silicone sealants are non-self-leveling sealants, which must be tooled into the reservoir so as to adhere adequately to the faces of the joint and contact the backer rod. The tooling device is typically a hose or large-diameter backer rod that smooths the silicone into the reservoir and against the joint sidewalls (see right image of Figure 7). • Self-leveling sealants theoretically do not require tooling but instead rely upon the flowability of the material, which allows it to settle into the joint reservoir created by the uniform joint width, and proper backer rod installation. Both tooled and self-leveling silicone sealants must be finished in a recessed configuration, as described previously (Smith et al. 2014). Silicone sealants require adequate curing time before Figure 6. Bond strength test results versus corresponding moisture content (Kim, Bhardwaj, and Zollinger 2018).

20 Portland Cement Concrete Pavement Joint Sealant Practices and Performance opening the pavement to traffic. Manufacturer recommendations for application, depth of recessed configuration, and curing time should be followed. Preformed seals—Figure 8 shows a cross-section of a preformed neoprene seal. The proper installation of these seals is relatively straightforward because they have no special thermal or curing requirements. Instead, these seals are compressed into the reservoir and remain in that state of compression over their service life. Thus, it is important that the compression seal is properly sized for the joint. Adequate compression creates a secure seal between the faces of the reservoir and the neoprene sealant. To be effective, the neoprene seal should maintain a state of compression, typically Figure 7. Hot-pour (L) and silicone sealant (R) installations [ACPA 2018 (L); Smith et al. 2014 (R)]. Figure 8. Preformed compression seal (ACPA 2018).

Literature Review 21   between 20 percent and 50 percent of its width (ACPA 2018). Thus, ambient temperature at installation is important. Because the seal should be in compression even during cold tempera- tures, the seal may need to be installed at 50 percent compression if seasonal low temperatures are significantly lower than the installation temperature. To install (compress and insert) the neoprene seal without damaging it, the sealant is often lubricated before insertion. If the sealant is installed straight and vertically into the joint, the use of lubrication should allow the seal to compress adequately. Joint Sealant Performance Sealing joints is widely believed to be beneficial to concrete pavement performance in two ways (Morian and Stoffels 1998). First, it minimizes water infiltration into the pavement structure. The presence of moisture in a pavement structure can initiate support issues that may decrease pavement service life. In a study on the effectiveness of sealed joints in reducing chloride intrusion, concrete slabs with unsealed joints had the highest rate of corrosion density (Abo-Qaidis and Al-Qadi 1995). Second, it has long been accepted that sealed joints reduce the infiltration of larger-size incompressible material (i.e., sand, small stones, and debris) into the joints, which could lead to spalling (Morian and Stoffels 1998); however, it is more likely that they also reduce the build-up of fine dirt on the face of the joint, thereby reducing the tendency for shoving to develop at the joint. The accumulation of incompressible materials of this nature could eventually lead to pavement blowup distress when expansion occurs because of a change in slab temperature. Other factors that affect performance are elaborated in the following discussion. Effect of Joint Seals on Pavement Performance Sealing and resealing of PCC pavement joints and cracks are considered an important part of the maintenance of the pavement. However, some have suggested that sealing may not be cost-effective (Fang et al. 2003). Nonetheless, the general view of joint sealing is that it increases the service life of concrete pavements. This view is supported by performance benefits such as the following: • Joint seals limit the amount of surface water coming into the paving system, reducing the risk of pumping, erosion, D-cracking, or any other moisture intrusion deterioration (see Figure 9). Properly installed and maintained joint seals allow water to drain sufficiently from critical locations (e.g., areas near the joint) by limiting infiltration rates. A study of pavement test sections in the Long-Term Pavement Performance (LTPP) program indicates that favor- able drainage (as characterized by the AASHTO Drainage Coefficient) is a common feature of well-performing JPCP (Khazanovich et al. 1998). A recent study conducted at Texas A&M University confirmed that properly installed joint seals can be very effective in preventing moisture infiltration and thus performance issues related to erosion damage (Bakhsh and Zollinger 2015). • Joint seals restrict the entry and lodging of incompressible materials (such as dirt, rocks, and other debris) from entering and becoming lodged in the joint. The presence of these incompressible materials in the joint during thermal expansion periods can lead to localized distress such as spalling or blowups. • By limiting water intrusion, joint seals also limit the intrusion of deicing chemicals used for snow/ice control in cold climates. The National Concrete Pavement Technology Center finds that the use of deicing techniques contributes to more joint distress than occurs in concrete pavement that has not been exposed to deicing chemicals (Taylor et al. 2012). Furthermore, use of deicing chemicals in combination with freeze-thaw cycling may lead to various forms of damage and deterioration, different from D-cracking.

22 Portland Cement Concrete Pavement Joint Sealant Practices and Performance • The benefits and cost-effectiveness of joint sealing have been debated since the 1970s. The need for concrete paving joint sealing is likely project-specific and related to the type of pavement, pavement section (including the drainage, erodibility, and frost resistance of the foundation materials), the local environment, the level of heavy truck traffic, and the required level of service and performance. Analysis of FHWA’s LTPP data reveals that a pavement’s foundation (subgrade, subbase, or both) is one of the most critical design factors in achieving excellent performance for any type of pavement (ACPA 2007). For pavement designers, one of the most important elements in optimizing the design of concrete pavements is the assumption that the use of joint sealants will in fact protect the supporting layers from the infiltration of water during rainfall events. The Pavement ME software includes an input with regard to this factor, which recognizes the need for properly functioning joint sealant systems. These types of considerations are necessary for ascertaining the need and appropriate sealant to use for a given project. Because of its rigidity, concrete pavement has a high degree of load-spreading capacity that typically results in low sublayer stresses and the potential for concrete pavement slabs to provide adequate performance even if placed directly on a compacted, natural subgrade. However, in order to ensure that adequate subgrade support will prevail, the need for joint sealing clearly should also be coordinated with any requirements for improved subgrade stabilization or the inclusion of an additional sublayer. These supporting layers should provide a stable construction platform, uniform slab support, and sufficient erosion resistance. Infiltration into a pavement structure could also result in subbase erosion, loss of support, and loss of joint stiffness (Olson and Roberson 2003). For example, faulting is considered to be a serious failure in jointed concrete pavement and is directly related to the presence of water below the slab. Accumulation of water under a slab combined with traffic loading can initiate erosion along the interface between the base and the slab, particularly during the times in a 24-hour cycle when the slab is separated from the base layer along the slab edges and corners. Figure 9. Examples of saturated base (L) under a joint in JPCP and deterioration (R) evident below the joint sealant (Taylor et al. 2012).

Literature Review 23   Longitudinal cracking, corner breaks, and freeze-thaw damage are other examples of distress related to moisture trapped in pavement at the joints (Qi, Weiss, and Olek 2003). Sublayer erosion potential, which leads to faulting and potential slab cracking, is one of the key factors that need to be considered regarding joint sealing (Figure 10). Although few tools are presently available to assess erosion potential, the main elements of erosion are the effective- ness of the joint sealing, the rate of erosion of the subbase or subgrade material, the existence of moisture under the slab, and traffic loads (Figure 10) (Bakhsh, Zollinger, and Jung 2013). Therefore, erosion is clearly linked to drainage and the effectiveness of the joint seal, which both limit water infiltration. Erosion potential and the accumulation of water along the slab-subbase interface combined with passing traffic can often initiate pumping, the transporting of eroded material, and finally the faulting of the joint. Pumping involves the transportation of abraded material from beneath the slab, typically voiding the slab support in the vicinity of a joint. Erosion of slab support can often lead to high deflections and possibly other types of distress, such as spalling of the joint and acceleration of the loss of load transfer and bond between the slab and the sublayer, which shorten the life of the pavement (ACPA 2007; Hall et al. 2008; Jung and Zollinger 2011). Infiltration of moisture in a pavement joint may ultimately lead to erosion damage and increase the potential for pavement blowup distress. Sealant Type–Related Performance Hot rubberized asphalt products usually have strong sealing characteristics and fairly low-cost versatility; however, when they age, water penetration becomes possible as flexibility and bonding along the seal-joint wall interface decrease over time (Bakhsh, Zollinger, and Jung 2013). Most states use certain kinds of asphalt to seal and reseal cracks and joints, but the possibility of failure increases unless the sealant is properly installed (Peterson 1982). If properly installed, the hot- pour joint sealant may be effective for at least a period of time. According to an FHWA study, 75 percent of the installed sealants lasted nearly 9 years but with considerable variance in their service life (Smith and Romine 1999). Various factors such as installation, climatic conditions, and traffic level played a role in the serviceability of the joint sealants. In another sealant study by the California DOT (Caltrans), the rubber seals were still in good condition after 10 years of service (Caltrans 2012). Erosion and Faulting Water Traffic Loads Erodible Medium Pathway for Water Figure 10. Main elements contributing to subbase erosion and PCC faulting.

24 Portland Cement Concrete Pavement Joint Sealant Practices and Performance Silicone-based sealant materials can have good durability and bonding characteristics if properly installed. This type of sealant material may also be simpler to install than asphalt sealants. Silicone sealants can also have less sensitivity to aging and temperature effects (Brown 1991; Lynch, Chehovits, and Luders 2002). Although silicone is more costly than hot-pour asphalt, it tends to yield longer service life. An LTPP study involving silicone-based joints in Arizona has shown excellent joint sealant performance over a service period of more than 20 years (ARA 2013). That study is part of the Arizona Special Pavement Studies (SPS-2) at a site installed in 1993 with 12 LTPP and 9 ADOT test sections. Each test section comprises about 33 transverse joints that were sealed with silicone sealant (non-sag). Several base type, concrete strength, and slab thickness combinations were constructed to identify the degree of each factor’s contributions. An assessment of the joints and seals, carried out in March 2013, finds the overall performance of the sealants to be surprisingly good, with some seals in service for more than 20 years in the truck lane carrying approximately 31 million equivalent single-axle loads. Figure 11 shows the percentage of sealant failure for each section, showing a total failure of not more than 35 percent (ARA 2013). Compression sealants are designed to remain tight in the joint reservoir when the joint is at its maximum opening and to recover from the compressive strain when the opening is at its smallest during the hot summer months. Preformed compression seals usually have a long life when the sealant is compressed (in the appropriate range between 20 percent and 50 percent of its original width); therefore, these types of sealants must be installed to function properly according to expected joint movements. It is important that these types of sealants retain the necessary elasticity over this range of movement. Compression sealants are probably more resistant to weather, sunlight, oils, chemicals, thermal heat, abrasion, and impact deterioration and hydrostatic pressure than are other types of sealants. A study by the Michigan DOT on various concrete pavement joint sealants concludes that preformed compression sealant performed better than other sealant types (Eacker and Bennett 2000). From an economical perspective, however, compressed sealants are the most expensive choice, and asphalt base sealants are comparatively less costly. Sealant Cohesive and Adhesive Failure This section addresses briefly the causes and failure mechanisms of sealant distress types. In order to evaluate sealant effectiveness during the service life, there is a need to identify and Figure 11. Overall failure rates of transverse joints, Arizona (ARA 2013).

Literature Review 25   evaluate the effects of different factors on sealant failure. As stated earlier, three different types of sealants are primarily used: asphalt-based sealants, silicone-based sealants, and preformed compression sealants. Sealants typically undergo two types of failure mechanisms: cohesive failure and adhesive failure. Cohesive failure is defined as a failure within the sealant matrix if the stress within the sealant exceeds the sealant tensile strength (see Figure 12). Sealant stress is caused by two factors: (a) horizontal stress caused by the movement of the concrete slab and (b) vertical shear stress generated by traffic loading. For both conditions, the strain (and subsequently the loading rate) is relatively low. Consequently, properly installed sealants tend to resist cohesive failure (Li 2012). An adhesive failure is defined as a failure at the sealant-concrete interface (see Figure 13). Bond (adhesive) strength is affected mainly by the adhesion properties of the sealant. Rough concrete surfaces increase the contact area between concrete and sealant, thus increasing the overall adhesion resistance to bond failure. Fragmentation in the joint reduces the contact area between the slab and the sealant, which adheres to the foreign object instead of the concrete. Generally, a clean surface should be used for good adhesion (Li 2012). This type of adhesive failure happens at an early age and therefore can be classified as a premature failure (Gurjar, Tang, and Zollinger 1997; Li 2012). Although some fieldwork has reported that sealants may not have long service life, two unique studies have recently confirmed that correct installation of sealants can result in a 20-year service life. One of the studies was FHWA’s LTPP SPS-2 Experiment in Phoenix, Arizona, mentioned previously (ARA 2013). The other study was carried out under the U.S. Army Corps of Engineers Construct Productivity Advanced Research program at Fairchild Air Force Base in Spokane, Washington (Lynch et al. 2013) in 1989. This study consisted of laboratory and field assessments of both hot-pour and silicone sealants. The silicone sealants were convention- ally installed, and the hot-pour sealants were flush-filled. Both sealant types had a lifespan of more than 21 years, and only 5 percent of the installed length experienced cohesion or adhesion failure (Lynch et al. 2013). Figure 12. An example and mechanism of cohesive failure in sealants.

26 Portland Cement Concrete Pavement Joint Sealant Practices and Performance The results of these two studies show that appropriate installation can yield sealants with a service life of more than 20 years. Previously, little factual evidence existed to indicate the type of serviceability possibilities, but these findings confirm and document that sealants can last much longer than present service-level expectations (Ioannides, Long, and Minkarah 2004; Lynch et al. 2013). Improperly installed sealants often undergo premature deterioration because of weather and traffic (Gurjar, Tang, and Zollinger 1997; Hawkins, Ioannides, and Minkarah 2001). Any moisture on the bond interfaces or excessive humidity can inhibit full adhesion potential (Gurjar et al. 1998). Before the installation of the joint seal, joint reservoir walls should be cleaned to prevent contamination of the sealant materials affecting the bond to the joint wall (Morian and Stoffels 1998). Table 4 summarizes factors and causes of sealant failure. Although sealant material plays an important role, sealant failure is not always related to sealant material properties. Researchers have noticed that sealant failure can be due to underestimating a joint’s movement character- istics rather than to defects of the sealant material itself (Cook, Minkarah, and McDonough 1981). Failure may occur when the joint’s opening is wider than the extension characteristics of the sealant or if the sealant is too bulky to allow for the joint to close fully. Researchers have also found that, for sealants with higher depth-to-width ratios, adhesion failure is likely to occur at the contact region between the seal and the joint wall (Tons 1959; Cook, Minkarah, and McDonough 1981; Khuri 1993; Woo Lee and Stoffels 2001; Kim and Zollinger 2020). Maintenance (Resealing) Applications When pavement condition surveys determine that joint sealant damage density is high enough, measures should be taken to restore the functionality of the joint seal. State agencies may have specific distress levels to trigger repair considerations along with cost and traffic control factors to assist in this decision (ACPA 2018). Figure 13. An example and mechanism of adhesive failure in sealants.

Literature Review 27   Selecting Materials and Equipment for Resealing The selection of sealant for resealing is similar to the selection of a sealant for new construction, except that preformed sealants are typically not used in resealing operations. Older pavement in good condition can present some issues for preformed seals, most notably in terms of variable and nonuniform joint widths and the presence of joint spalling. Resealing operations tend to be expensive because of the cost of the material, labor, con- struction, joint widening, and lane closures. Lane closure costs depend on both time and traffic levels. Shober (1997) notes that the cost over a 10-year period to maintain a sealed pavement (sawing and sealing a joint reservoir when needed) is up to 45 percent more than for a similar unsealed pavement. However, there is also a cost associated with base erosion, Factor Cause Failure Type Factors related to sealant material properties Low bond strength between sealant material and joint reservoir Adhesive failure Low cohesiveness (separation between sealant material itself) Cohesive failure Lack of sealant material’s extension capacity Adhesive/cohesive failure Climatic factors (solar radiation, temperature changes, and so forth) Weathering and aging (stiffening and losing flexibility) Crack initiation in the middle of the sealant (cohesive failure) Factors related to construction and installation Existence of moisture at the joint wall before installation Premature failure (adhesive) Dirt on the joint wall before installation Premature failure (adhesive) Factors related to pavement, joint, and sealant design Sealant size and geometry (depth-to-width ratio) Affects stress distributions; leads to fatigue (cohesive failure) Joint width too wide; compression sealant not adequately compressed Sealant displacement Joint width too narrow during summer; sealant excessively compressed Sealant press/damage Traffic- and load- related factors Slabs with faulted joints during cooler periods when joints are the widest Adhesive/cohesive failure Joint distresses Spalling, corner breaks, and so forth that directly debond the sealant from the joint reservoir Sealant debonding Sealants’ chemical reactions Destructive chemical reactions between sealant materials and fuel or engine oils, particularly jet fuels in airfields Stiffening (cohesive failure) Table 4. Factors and causes of sealant failure (Bakhsh and Zollinger 2015).

28 Portland Cement Concrete Pavement Joint Sealant Practices and Performance which should be considered as well when comparing sealed and unsealed pavement main- tenance costs. Construction Considerations The resealing process is similar to the new sealing process described earlier, with two further steps. Those additional steps are the removal of the old sealant material and the refacing of the reservoir to accept new sealant material. Once these steps have been completed, the joint resealing follows the steps of joint cleaning, preparation, and material installation discussed previously. Removal of old sealant—During the joint refacing operation, old sealant can be removed by a rectangular joint plow (see left image in Figure 14) or a diamond-bladed saw (see right image in Figure 14). The latter has come into more widespread use because it is more efficient and does not damage the joint. Joint refacing—The surface finishing of the joint reservoir, refacing, provides a clean, con- tinuous surface to which the replacement sealant can be effectively bonded. Refacing operations typically use a diamond-bladed saw; however, because of the need to slightly widen the joint, multiple blades should be on hand to provide the desired cutting width. Smith et al. (2014) recommend that refacing should widen the reservoir by no more than 0.08 in. (2 mm) to speed operations and limit the joint width after multiple resealing operations. Preparation and Installation of New Sealant Following the refacing of the joint reservoir, the remaining steps in the resealing process follow the steps described earlier for the preparation and installation of new joint seals. When suitable material is chosen for resealing, resealing has the same degree of difficulty as the instal- lation of new sealants. Figure 14. Removal of old sealant: joint plow (L) and diamond-bladed saw (R) (Taylor et al. 2012).

Literature Review 29   Alternative Methods Saw and sealing operations have been estimated to be between 2 percent and 7 percent of initial construction costs (Hall et al. 2008). A study on the relative costs of concrete highway construction features indicates that the relative cost (for a given design feature based on refer- ence pavement section) for silicone sealed joints is approximately 7 percent more than that of unsealed joints. According to the study, the cost is even higher if more expensive sealant materials are used (e.g., the most expensive sealant option was found to be ½-in. compression sealant) (Scofield 2010). One alternative method proposed by some state DOTs is to reduce costs by cutting narrow joints with a single pass and leaving them unsealed. This approach is used by WisDOT, which avoids making wide sawcuts. In 1990, for new construction and maintenance, WisDOT adopted a policy to remove all PCC joint sealing (Rutkowski 1990). According to a report by Shober (1997), this “no-seal” policy has saved Wisconsin $6 million annually, while causing no loss in pavement performance and achieving increased customer safety and convenience. With additional experience, WisDOT now seals joints on low-speed roads (less than 45 mph) but still uses open joints on high-speed roadways (ACPA 2018; FHWA 2019). A second alternative is to use narrow joints but to fill them with sealant. In this configura- tion, the sealant attempts to adhere to the sides as well as the bottom of the sawcut; it saves the expense of the second wider sawcut but places the sealant in a high state of debonding stress. In recent years the construction of narrower joints has become more common. A Caltrans joint and sealant evaluation shows that joints with the narrowest width (1⁄8 in.) had the least amount of distress. Also, these joints have functioned well even in areas of high-temperature variations (as in the Central Valley, which experiences an 80° temperature swing) over the course of a year (Caltrans 2012). This finding contradicts existing design specifications and deserves further investigation. Although little information is available on the magnitude of the annual joint opening, it can be assumed to be low enough to minimize debonding failure. A third alternative is to have narrow-sealed joints that consist of single sawcuts with a narrow backer rod and sealant installed. The backer rod gives the sealant better support and helps it lay with a structurally better shape, which can distribute the stresses more effectively. These alternatives are intended to reduce initial cost and not necessarily to enhance perfor- mance. These three alternatives (presented in order of increased cost) remove the second sawing operation required to form a sealant reservoir and the additional sealant material needed to fill the reservoir (Morian and Stoffels 1998).