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Joint Sealant Evaluation

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Joint sealant evaluation usually requires examining three areas: the bonding conditions, the presence of incom­pressibles and the condition of the adjacent concrete. Many agencies evaluate sealant as either good or bad, with no middle ground. A problem in any one of the three areas is considered failure of the sealant without regard to overall performance [1].

Distress

Distress is a more appropriate depiction of the sealant and spall-related problems that occur. A pro­blem may exist in some quantity, but not to such an extent as to consider the joint or sealant failed. Sealant perfection is not a realistic goal and sealant failure is more accurately determined from ac­cumulated sealant distress. Accumulated distress limits effectiveness and may initiate pumping, faulting, spalling, etc.

Sealant distresses include:

  • Adhesion loss: the loss of bond between the sealant material and the concrete joint face. Adhesion loss is noted by the physical separa­tion of the sealant from either or both joint faces.
  • Cohesion loss: the loss of internal bond within the sealant material. A noticeable tear along the surface and through the depth of the sealant is evidence of cohesion loss.
  • Oxidation/Hardening: the degradation of the sealant as a result of natural aging, long-term exposure to oxygen, ozone, ultra-violet radiation and/or the embedment of incompressibles into the sealant material [2]. Oxidation/hardening is noted by a crusted surface and the loss of flex­ibility. The crust or hardening often extends through the entire width and depth of the material. The sealant may be cracked into small segments and missing from the reservoir. Embedded incompressibles produce similar degradation characteristics.


Investigation for spalling of the surrounding concrete is also a necessary in sealant evaluation. Spalling typically arises when material enters the joint during cooler temperatures [3][4]. When adjacent slabs ex­pand at higher temperatures, incompressibles inhibit expansive movement that normally results in joint closure. This induces high compressive stresses along the joint face and may break or chip the con­crete. Other material that can prohibit joint closure includes dried residue from sawing or patching operations. Small spalls are termed sliver spalls. The width of sliver spalling is typically from 1/8 - 1/4 in. (3 -13 mm) (Figure 7).

Incompressible infiltration results from either spall or sealant-related problems and is not considered a distress mode. The presence of incompressibles indicates other problems. In certain instances the presence of incompressibles can contribute to sealant failure through the working action of traffic. Sealant hardening through incompressible embed­ment is a good example. Incompressible rating criteria are [5]:

  • None: No incompressibles are present. Minimal: Some incompressibles are present, but their presence does not appear to affect the joint or sealant performance.
  • Moderate: Incompressibles are present and may be contributing to sealant distress and/or spalling exhibited along the joint.
  • Extensive: Many incompressibles are present in the joint. Judgement is that they are contribut­ing to significant sealant distress, loss of sealant, and/or joint spalling.


Sealant Condition Survey

Figure 7. Minor spalling found on some sealant installations is much smaller than classic spalling and not considered large enough to affect the performance of the pavement.

Resealing is necessary when sealant distress affects average sealant condition and results in significant water and incompressible infiltration. The basis of this determination is typically engineering judgement. Consequently, the importance of scheduled reviews by agency personnel to monitor sealant condition cannot be overemphasized [6][7].

An agency may also employ a rational rating system. A system bases the decision to reseal on an average rating of a representative number of joints [8]. A survey crew must rate the joints for sealant distress, joint spalling and incompressible presence.

Sealant surveys should consist of basic distress data collection, with concentration at the joints. The crew should take measurements of joint faulting and joint width. The system should require visual and physical examination of the joint and sealant.

Adhesion loss is the most common distress [9][10][11][12]. A dull knife blade or thin metal strip provides an excellent tool for checking sealant adherence (Figure 8) [13][14]. Four to five penetra­tions of the knife at random locations along each joint provides a good sample. The feel of the penetration provides a sense of the sealant adhesion. A loose, effortless penetration indicates adhesion loss, while good adhesion provides resistance. Further examination of the knife blade may identify the presence of incompressibles or dust along the joint walls and below the sealant.

Figure 8. Checking for sealant adherence with a dull knife blade or thin metal strip [15].

Rating cohesion loss and the presence of incom­pressibles requires visual examination only. On occasion some knife penetration may be necessary to check the depth of cohesion separations seen on the sealant surface.

The surveyors must also check the material for signs of hardening. A sample of the hardened material ex­tracted from the joint can identify the cause. Harden­ing may be a result of oxidation or incompressibles embedded in the material.

The presence of incompressibles may sometimes be difficult to assess because some agencies sand road­ways for snowy conditions. Road sand mixtures spread across a pavement collect in the joints. A broom may be needed to remove incompressibles in order to view the sealant. This is especially true where seals are properly recessed. Under these con­ditions, incompressible evaluation requires judgement and should not be influenced by the presence of traction control sand.

The crew should record the presence of spalling for the entire length of each joint. Evaluating spall sever­ity and considering patching needs are important aspects in this effort. Notes of joints needing patch­ing are also important in the final assessment of the pavement condition. Reference 33[16] provides good guidance to determine the severity of typical spalls.

Be careful in noting sliver spall presence. On occa­sion popouts have been mistaken for the tiny spalls. Usually the sealant will remain in the joint despite sliver spalling. This makes evaluating the sealant/joint condition difficult. It requires good judgement to determine if these tiny spalls are effecting pavement condition.

Evaluation of a representative number of joints is necessary to accurately characterize the degree of sealant degradation. Table 7 provides random and area samples needed for statistical significance in a sealant/joint survey [17]. The average sealant condi­tion from the surveyed joints provides a trigger for resealing necessity.

Table 7. Random and area evaluation samples needed for statistical significance in sealant/joint survey (34).
Joint Spacing [ft(m)] Measurement Interval Number of Joints Area
<12 (<3.7) Every 9th joint >85/mi (>50/km) 20%*
12-15 (3.7-4.6) Every 7th joint 85-70/mi (50-43/km) 20%*
15-20 (4.6-6.1) Every 5th joint 70-50/mi (43-33/km) 20%*
20-30 (6.1-9.1) Every 4th joint 50-35/mi (33-22/km) 20%*
30+ (9.1+) Every 4th joint 35/mi (22/km) 20%*
*Surveyors should select an area (sample unit) that represents the average condition of the pavement in question.

The length of deterioration defines the severity level of deterioration along each joint [18]. A low severity exists if less than 25 percent of the length of any joint seal is damaged. A moderate condition exists with 25 - 50 percent damage. Above 50 percent damaged is considered high severity.

An unexpected increase in joint faulting or spalling may also identify a project in need of sealant replacement. Periodic faulting measurement allows a histogram of joint faulting and/or spalling to convey such changes. An increased faulting rate may be due to the presence of more water or incom­pressibles from poor joint seals. (Although this iden­tification is effective, it is often made too late after distress inhibits service life.)

Some sealants may remain tight in the reservoir, but still lose adhesion to the side walls [19]. Many surveyors would call this failure of the sealant. However, assessment of the joint can often show that little damage is occurring as a result of the bond loss. The incompressibles rating is a good indicator under this situation. Where the rating is minimal to moderate, the sealant is likely still performing satisfactorily.

Researchers in Kansas use a vacuum tester to check seal tightness. They spread a soapy solution on the joint to identify leaks under vacuum. They measure the pressure developed within the tester housing to indicate seal effectiveness. The equipment develops a pressure of 27 in (69 cm) water at no air flow (full seal) and 10 in (25 cm) water at free air flow (no seal). Figure 9 shows the average results on different sealants one year after installation [20]. Although some sealants have less leakage than others, none provides a complete seal.

Performance

Hot-pour Liquid - A typical hot-pour sealant pro­vides on average from 3-5 years life after proper in­stallation [21][22]. One report discusses good observ­ed performance of low-modulus or PVC coal-tar bas­ed products past 8 years [23]. Unfortunately, overall hot-pour sealant performance has been inconsistent. The most noted problems are adhesion or cohesion loss, and inconsistent field properties.

Cohesion loss is not unusual in narrow and deep joints. Many agencies provide a single reservoir cut to 1/3 or 1/4 the slab depth. The agency specifies pouring a hot-pour sealant directly into the saw cut. The single cut is difficult to clean and the shape fac­tor (ratio of depth to width) can approach 25. Cohe­sion loss is not unusual in these situations. At early ages, tensile stresses from joint opening may over­come cohesion in an improperly shaped sealant before overcoming the bond (Figure 10) [24]. Hot-pour materials typically perform better with a shape factor of one.

All hot-pour sealants are subject to variances in field preparation. Heating temperature during preparation is extremely important. Overheating can change sealant properties. Overheating polymeric hot-pour sealants cause the polymers to decompose. Upon cooling the sealant may not have the intended modulus or provide the intended adhesion. Evidence of this can be noted by different performance of the sealant along different locations on a project [25].

Figure 9. Average results of Kansas vacuum tests on different sealants one year after installation [26]. Note that no sealant provided a completely tight seal.
Figure 10. A large shape factor induces high internal tensile stresses from joint opening and results in cohesion loss. (Also note no backer rod - poor practice).

PVC coal tar sealants are self healing against small tears [27][28]. Observing their condition can be challenging because hot weather may hide adhesion or cohesion loss.

Silicones - Silicone sealants have performed well for periods exceeding 8-10 years on roadways [29][30][31]. Installations on airports generate similar results. Good performance hinges on joint prepara­tion. Of extreme importance is that the joint be clean and dry at the time of installation.

Poor joint preparation results in inadequate bonding of the sealant to the reservoir walls. Traffic may disturb poorly bonded silicone by pulling it from the joint. In some cases a silicone may recess into the reservoir by suction created by deflection and rebound of joints under load [32].

Sliver spalling has been noted on highway and air­port joints sealed with silicone sealants. At one test site, joints sealed with silicone contained 10 times more sliver spalling than the other liquid sealants [33]. On that test site, the spalling appeared during the first year of service and did not significantly in­crease with time. Sliver spalling has not impacted the pavement performance on the test site and will not likely threaten pavement life. Its cause is unknown and requires future research.

In some infrequent past cases, silicone sealants did not cure evenly after installation [34]. When this occurred the upper portion of the sealant cured well while the lower portion remained soft and tacky. Consequently the lower portion did not bond well to the reservoir walls. While these cases have been infrequent and have not been observed In many years, it is still ad­visable to sample sealant within 14 to 21 days after installation [35]. Performance of most joints with in­adequately cured silicone is still satisfactory [36].

Figure 11. A typical five cell seal cross-section [37].

Compression seals - Compression seals provide service for periods often exceeding 15 years and some­times 20 years [38][39]. Five-celled seals provide the most consistent long-term performance. Figure 11 shows a cross-section of a typical five cell seal.

Compression seals require that joint faces be in good condition. Perpendicular faces of uniform width are necessary for optimal performance. A seal can work its way up out of a nonuniform reservoir. A contractor can easily attain the necessary uniformity in new construction, but it may be difficult in rehabilitation. For this reason, compression seals are not typically used in resealing operations [40].

Preformed seals may lose elasticity and develop compression set over an extended time [41]. This occurs when the seal loses its compressive recovery and no longer places outward pressure on the side walls. The seal begins to lose effectiveness and may be dislodged. Avoiding stretch during installation and using a proper seal size reduces compression set potential. Compression greater than 50 percent may induce compression set because webs stick together and prevent rebound [42]. In some cases compression set has been attributed to improper chemical formulation during manufacture [43].

References

  1. Loza, G.F., Anderson, D.I., "Evaluation of Concrete Joint Sealants Clear Creek Summit to Belknap Interchange," Utah Department of Transportation, March 1988.
  2. "Joint Sealing a Glossary," Highway Research Board, National Academy of Sciences, Special Report 112, Washington D.C., 1970.
  3. Eres Consultants, Inc., "Techniques for Pavement Rehabilitation," Federal Highway Administration, 1992.
  4. "Field Inspection Guide for Restoration of Jointed Concrete Pavements," Demonstration Projects Division, Federal Highway Administration, Washington D.C., December 1987.
  5. Voigt, G.F., Yrjanson, W.A., "Concrete Joint Sealant Performance Evaluation," Utah Department of Transportation, July 1992.
  6. "Maintenance of Joints and Cracks in Concrete Pavement," IS188.01P, Portland Cement Association, Skokie, IL, 1976.
  7. Peterson, D.E., "Resealing Joints and Cracks in Rigid and Flexible Pavements," Synthesis of Highway Practice 98, National Cooperative Highway Research Program, Transportation Research Board, National Research Council, Washington D.C., December 1982.
  8. Brunner, R.J., Kileraski, W.P., Mellott, D.B., "Concrete Pavement Jointing & Sealing Methods," Transportation Research Record 535, Transportation Research Board, National Research Council, Washington D.C., 1975, pp. 24-34.
  9. Peterson, D.E., "Resealing Joints and Cracks in Rigid and Flexible Pavements," Synthesis of Highway Practice 98, National Cooperative Highway Research Program, Transportation Research Board, National Research Council, Washington D.C., December 1982.
  10. Rutkowski, T.S., "Joint Sealant Study," Wisconsin Department of Transportation, May 1990.
  11. Hicks, S.E., "Do We Need to Sea! Joints?," State Highway Commission of Wisconsin, January 1967.
  12. Voigt, G.F., Yrjanson, W.A., "Concrete Joint Sealant Performance Evaluation," Utah Department of Transportation, July 1992.
  13. Darter, M.I., Carpenter, S.H., Zimmer, T.R., "Field Performance of a Low-Modulus Silicone Highway Sealant," Transportation Research Record 990, Transportation Research Board, National Research Council, Washington D.C., 1984, pp. 31-37.
  14. Voigt, G.F., Yrjanson, W.A., "Concrete Joint Sealant Performance Evaluation," Utah Department of Transportation, July 1992.
  15. Darter, M.I., Carpenter, S.H., Zimmer, T.R., "Field Performance of a Low-Modulus Silicone Highway Sealant," Transportation Research Record 990, Transportation Research Board, National Research Council, Washington D.C., 1984, pp. 31-37.
  16. "Distress Identification Manual for the Long-Term Pavement Performance Studies," SHRPLTPP/ FR-90-001, Strategic Highway Research Program, National Research Council, Washington D.C., 1990.
  17. "Diamond Grinding & CPR 2000," TB-008.0CPR, American Concrete Pavement Association, Arlington Heights, IL, 1990.
  18. "Distress Identification Manual for the Long-Term Pavement Performance Studies," SHRPLTPP/ FR-90-001, Strategic Highway Research Program, National Research Council, Washington D.C., 1990.
  19. Voigt, G.F., Yrjanson, W.A., "Concrete Joint Sealant Performance Evaluation," Utah Department of Transportation, July 1992.
  20. Wojakowski, J.B., "Joint Sealant Test Sections - US 36 Doniphan County," NEPT KS-8904, Kansas Department of Transportation, Unpublished Research Data, 1991.
  21. "Performance of Jointed Concrete Pavements," Volume I - Evaluation of Concrete Pavement Performance and Design Features, FHWARD-89-136, Federal Highway Administration, McClean, VA, March 1990.
  22. Voigt, G.F., Yrjanson, W.A., "Concrete Joint Sealant Performance Evaluation," Utah Department of Transportation, July 1992.
  23. Voigt, G.F., Yrjanson, W.A., "Concrete Joint Sealant Performance Evaluation," Utah Department of Transportation, July 1992.
  24. Voigt, G.F., Yrjanson, W.A., "Concrete Joint Sealant Performance Evaluation," Utah Department of Transportation, July 1992.
  25. Voigt, G.F., Yrjanson, W.A., "Concrete Joint Sealant Performance Evaluation," Utah Department of Transportation, July 1992.
  26. Wojakowski, J.B., "Joint Sealant Test Sections - US 36 Doniphan County," NEPT KS-8904, Kansas Department of Transportation, Unpublished Research Data, 1991.
  27. Loza, G.F., Anderson, D.I., "Evaluation of Concrete Joint Sealants Clear Creek Summit to Belknap Interchange," Utah Department of Transportation, March 1988.
  28. Godfrey, K.A., "Pavement Joint Seals," Civil Engineering, American Society of Civil Engineers, March 1972.
  29. Voigt, G.F., Yrjanson, W.A., "Concrete Joint Sealant Performance Evaluation," Utah Department of Transportation, July 1992.
  30. "Guide Specifications Dow Corning 888 Silicone Highway Joint Sealant," Dow Corning Corporation, 1992.
  31. "Silicone Sealant Performance Review," Federal Highway Administration, Pavement Division/Demonstration Projects Division, September 1990.
  32. Voigt, G.F., Yrjanson, W.A., "Concrete Joint Sealant Performance Evaluation," Utah Department of Transportation, July 1992.
  33. Voigt, G.F., Yrjanson, W.A., "Concrete Joint Sealant Performance Evaluation," Utah Department of Transportation, July 1992.
  34. "Silicone Sealant Performance Review," Federal Highway Administration, Pavement Division/Demonstration Projects Division, September 1990.
  35. "Silicone Sealant Performance Review," Federal Highway Administration, Pavement Division/Demonstration Projects Division, September 1990.
  36. "Silicone Sealant Performance Review," Federal Highway Administration, Pavement Division/Demonstration Projects Division, September 1990.
  37. "Design and Construction of Joints for Concrete Highways," American Concrete Pavement Association, Portland Cement Association, TB-010.0D, Arlington Heights, IL, 1991.
  38. Kiljan, J., "Concrete Pavement Restoration Demonstration," CDOH-DTD-R-88-6, Colorado Department of Highways, Denver, CO, February 1988.
  39. "Performance of Jointed Concrete Pavements," Volume I - Evaluation of Concrete Pavement Performance and Design Features, FHWARD-89-136, Federal Highway Administration, McClean, VA, March 1990.
  40. "Maintenance of Joints and Cracks in Concrete Pavement," IS188.01P, Portland Cement Association, Skokie, IL, 1976.
  41. Godfrey, K.A., "Pavement Joint Seals," Civil Engineering, American Society of Civil Engineers, March 1972.
  42. Eres Consultants, Inc., "Techniques for Pavement Rehabilitation," Federal Highway Administration, 1992.
  43. Godfrey, K.A., "Pavement Joint Seals," Civil Engineering, American Society of Civil Engineers, March 1972.