Field installation guidelines developed for asphalt crack sealants

Illinois Center for Transportation researchers have recently developed field installation guidelines to help pavement maintenance professionals select, install, and evaluate hot-poured crack sealant treatments for flexible pavements.

The Asphalt Crack Sealant Field Installation Guidelines were one of the outcomes of a second-phase pooled-fund study. The phase I study was initiated in 2002 and led by the Illinois Center for Transportation (ICT) of the University of Illinois at Urbana-Champaign (UIUC) and the National Research Council of Canada. The study was sponsored by a consortium of 11 U.S. state departments of transportation, 13 Canadian transportation agencies, and industry. The phase II study was initiated in 2010. The U.S. contribution was made through research projects TPF-5(045) and TPF-5 (225), sponsored by the Virginia Transportation Research Council.

In its initial phase, the study resulted in the development of several new fundamental tests that evaluated hot-poured asphalt crack sealants based on their rheological and mechanical properties over a wide range of service temperatures.

The tests, published as American Association of State Transportation Officials (AASHTO) specifications, include the following:

• AASHTO MP-25, Performance-Graded Hot-Poured Asphalt Crack Sealant (under review)
• AASHTO PP xx, Grading or Verifying the Sealant Grade (SG) of a Hot-Poured Asphalt Crack Sealants (under review)
• AASHTO TP 85, Apparent Viscosity of Hot-Poured Asphalt Crack Sealant Using Rotational Viscometer
• AASHTO TP 86, Accelerated Aging of Hot-Poured Asphalt Crack Sealants Using a Vacuum Oven
• AASHTO TP 87, Measure Low-Temperature Flexural Creep Stiffness of Hot-Poured Asphalt Crack Sealants by BBR
• AASHTO TP 88, Evaluation of the Low-Temperature Tensile Property of Hot-Poured Asphalt Crack Sealants by Direct Tension Test
• AASHTO TP 89, Measuring Adhesion of Hot-Poured Asphalt Crack Sealant Using Direct Adhesion Tester
• AASHTO TP 90, Measuring Interfacial Fracture Energy of Hot-Poured Crack Sealant Using a Blister Test
• AASHTO TP xx, Evaluation of the Tracking Resistance of Hot-Poured Asphalt Crack Sealants by Dynamic Shear Rheometer (DSR) (under review)

Building on the comprehensive tests and procedures developed in this initial phase, the researchers conducted field tests to validate the previously developed laboratory tests; determine thresholds using a diverse array of field performance data; and established guidelines for sealants installation and best practices.

An executive summary of Phase II findings, Validation of Hot-Poured Asphalt Crack Sealant Performance-Based Guidelines, is available of ICT’s website.

The field performance of 17 conventional sealants installed at five different sites in North America was investigated by the research team, led by Professor Imad Al-Qadi as Principal Investigator and research assistant professor Hasan Ozer. The researchers considered two types of treatment—crack filling, also known as clean and seal, and crack sealing, also known as rout and seal—and discussed all aspects of sealants installation, from planning and design to treatment and sealant selection, in addition to listing the equipment needed for crack sealing and filling.

The researchers listed several factors that should be taken into consideration at the planning and design stage. Such considerations include weather conditions, pavements pre-sealing conditions, traffic control, and safety concerns. In addition, they distinguished between the two available crack sealant treatments (i.e., clean and seal, and rout and seal) and presented recommended criteria for treatment selection following a “Sealant Grade” (SG) system established for selecting hot-poured crack sealant based on environmental conditions.

Detailed steps for crack sealant installation, including crack routing, crack cleaning and drying, materials handling and preparation, sealant installation, and blotting, in addition to a full list of the equipment needed in the process, are provided in the “Guidelines.”

Professor Ozer notes, “The sealant selection and installation guidelines was prepared by blending existing knowledge with the best practices learnt from the closely monitored test sections in various locations in the US and Canada.”

“The guidelines document serves as a comprehensive reference for pavement engineers, offering step-by step instructions for installing crack sealants,” says Professor Al-Qadi. “It encompasses a multitude of planning and design considerations that pavement maintenance engineers should be aware of at the onset of the project.”

 The complete reports of the findings of Phase I are available on ICT’s website: Adhesion Testing Procedure for Hot-Poured Crack Sealants, Development of Apparent Viscosity Test for Hot-Poured Crack Sealants, Characterization of Low Temperature Mechanical Properties of Crack Sealants Utilizing Direct Tension Test, and Characterization of Low Temperature Creep Properties of Crack Sealants Using Bending Beam Rheometry.