Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Civil and Environmental Engineering

First Advisor

John B. Metcalf


Coal-tar sealers are used to protect asphalt pavements from damage by fuel spillage. The durability of these coal-tar sealers has been limited by the formation of cracks that occur in both in trafficked and non-trafficked areas and in all climatic regions. This cracking severely limits the useful life of the coal-tar sealer. Various coal-tar mixtures were evaluated through existing standard test methods. The mixtures varied through the source of the coal-tar emulsion, amount of aggregate, and amount of polymer used in the mixtures. The material properties of these mixtures were determined through curing, thermal, bending, tensile and stress-relaxation testing. The material properties were determined using testing and evaluation methods either adapted from previous work or developed for this research. The initial goal of this research was to use the sealers material properties to develop parameters for a mechanistic design procedure. However, unresolved issues concerning the stress/strain behavior of the sealers during relatively small thermal movements and defining the formation and progress of cracks within the coal-tar sealer have prevented this. Instead the information gained during the field and laboratory evaluation of the various sealer mixtures was used along with the existing literature information to develop an expert system for specifying coal-tar sealers. The results of the evaluation showed that two coal-tar emulsion sealers meeting all current applicable specifications could have substantially different field performance. The amount of aggregate and polymer on the coal tar mixtures will affect the sealers performance. The sealer mixtures age or harden over time and cracking occurs through thermal movements resulting in a build up of stresses that the sealer cannot relax or dissipate. Generally, mixtures with higher amounts of aggregate and at least some polymer (acrylonitrile-butadiene) performed the best. The expert system provides a practical method for an engineer/designer to develop a systematic approach to selecting the type of sealer, material and design considerations, and construction methods. A guide specification that incorporates recommended test methods, materials, and application procedures is included as an appendix. The use of this system and guidelines is intended to provide an optimum coal-tar sealer mixture.