This chapter summarizes the study results, draws conclusions, and offers recommendations for further investigation. Crack sealing is one of the most common preventive preservation/
maintenance techniques in North America to extend pavement life. Most of the applied sealants fail adhesively at the crack walls. It is believed that adhesion occurs due to molecular and interatomic forces generated at the interface. Existing standards consider the adhesive
characteristics of sealants as part of sealant classifications. Various tests are currently applied to measure or predict sealant adhesive properties. Most of these tests apply loading (tensile, shear, bending, torsion, or peeling) or study the chemistry of the interfaces. However, these tests lack a true correlation with field performance or have not yet been validated using field data.
This study introduces the development procedure for an adhesive prediction test, tensile adhesive method (TAM) test. TAM test shows consistent results among specimens and operators. It provides consistent trends regarding the effect of temperature change and aging.
The following are the main findings of this study:
CSAT did not correlate well with sealants’ field performance.
Hot-poured sealants’ peak loads in TAM test show three patterns as the temperature decreases: drop for stiff sealants, increase for crumb rubber modified sealants, and remain constant for most of the sealants with a slight increase in the adhesive loads.
Sealant comparisons based on one temperature could be misleading.
Sealant repeatability for TAM test is significantly reduced for weak and very stiff sealants at relatively low temperatures.
Aging has a minimal effect on the adhesive characteristics. Hence, adhesive characteristics have a minimal change with respect to different test sites.
Specimen preparation has a significant effect on the adhesion characteristics of sealant.
Adequate contact area size and proper surface area cleaning are needed for any adhesion sealant test.
Sealant adhesive characteristics may not explain sealant field performance without considering other factors such as sealant installation, stiffness, and preservation maintenance program applied to the pavement. However, desired sealant field performance requires proper sealant adhesive characteristics.
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The following conclusions could be drawn from this study:
TAM test is a forward step in the direction of understanding the adhesive characteristics of hot-poured crack sealants. The test is repeatable and reproducible; it also addresses some of the CSAT specimen preparation limitation.
The TAM test results correlate well with field performance.
Sealant aging could be conservatively quantified using the vacuum oven method (AASHTO-TP-86-10 2015).
This study provides a basis for understanding the adhesive characteristics of hot-poured crack sealants. However, more work is needed. The following recommendations are expected to improve the common knowledge of the adhesive characteristics of hot-poured crack sealants.
Limited study was conducted on the sealant surface free energy and its relation to field performance. Further work is needed that may include other computational techniques for determining the surface free energy as well as other testing procedures.
An extensive study to validate the TAM test is needed.
Given that sealant is a viscoelastic material, test loading rate should be optimized.
Further research on sealant adhesive fracture mechanics is needed to better understand the failure mechanism at the interface.
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