Seal Coat Systems in Canada: performances and practice

Seal coat systems have been used in Canada and other countries for many decades. In fact, the development of the seal coat system is closely associated with the increased usage of the automobile as a means of transportation at the turn of the 20th century. Today it is the most common type of roadway surfacing in Canada. Seal coat is a thin wearing course made of superimposed layers of aggregate and bituminous binder. This type of treatment may be used to restore the surface characteristics of existing worn out roadway or to waterproof and preserve an existing roadway. They may be applied onto an existing bound material or an unbound road base. This type of treatment forms an impervious thin overlay over an existing bound or unbound surface. Seal coat systems may be divided into two families of treatments: the chip seal system and graded seal systems. Chip seals combine the application of a layer of calibrated chips onto a layer of a cationic rapid setting bitumen emulsion while the graded seals are systems that combine the application of a dense graded or gap graded aggregate onto a layer of anionic high float type bitumen emulsion. Each system may be applied as a single application or a multiple application. Seal coat systems may be applied at spread rates that range from 14 kg/m2 for a single chip seal applied onto an existing bituminous surface to 40 kg/m2 for a double high float seal treatment applied onto an unbound granular base. Many parameters such as the traffic and the existing surface conditions must be taken into account in the design of a specific seal coat system for a given roadway. Field adjustments are also very important; field conditions such as ambient temperature, the time of the year, the sun/cloud conditions must be taken into account as well. The success of this type of treatment is not only associated with the selection of an optimal design but also with the close attention to the local conditions during the field application. This paper presents an overview of the seal coating technologies and a discussion on the state of the practice including, design practices, construction procedures of these surface treatments in Canada and abroad. In addition, the paper introduces new concepts related to the selection of seal coating systems as well as the emerging chip sealing systems now available in North America.