Performance evaluation of a coating protection system for concrete structures affected by internal expansive reactions

In the last decades, a significant number of large concrete structures with deterioration problems, related to internal expansive chemical reactions, have been detected in Portugal. This type of degradation is associated with the formation of expansive products in concrete causing its disruption, leading to the decrease of the structure’s service life and, ultimately, to the decommissioning or demolition of the structure. In Portugal, structures affected by this pathology are very important in economic and strategic terms, since these reactions are usually encountered in large dams, bridges and viaducts. Two separate material-based mechanisms have been identified to cause the concrete swelling: Alkali-Silica Reaction (ASR) and Delayed Ettringite Formation (DEF). Both reactions result in the formation of expansive products and a common requirement for their occurrence is the presence of a sufficient moisture content inside concrete. By controlling the humidity level in concrete, coatings applied onto the concrete surface should contribute to mitigate ASR or DEF by acting as a barrier against ingress of water and allowing the concrete to dry, as long as they have adequate water permeability characteristics. This paper presents the general criteria that may be followed to select a surface protection system, based on coating materials (hereinafter designated by coating system), for the rehabilitation of concrete structures affected by expansive reactions, in order to mitigate them and, thus, contribute to improve durability and service life of affected structures. In addition, a laboratory study is presented concerning the performance evaluation of a surface protection system, composed of two coating materials, in terms of its capacity to bridge cracks, its permeability to liquid and to water vapour, and on its effectiveness on controlling humidity inside concrete.