Performance of a polymeric coating material applied to a concrete structure affected by internal expansive chemical reactions

Abstract

Currently, there is a significant number of large concrete structures with deterioration problems related to internal expansive chemical reactions (IECR), in Portugal and worldwide. This type of deteriorations is related to the formation of expansive products inside the concrete causing its premature deterioration due to expansion and cracking, which in turn accelerates the ingress of moisture and other aggressive agents into the concrete, leading to further deteriorations of the structure. Thus, IECR can reduce the service life of the structure and ultimately, lead to its decommissioning or demolition. Two main mechanisms have been identified to cause the concrete swelling: Alkali-Silica Reaction (ASR) and Internal Sulfate Reaction (ISR, heat-induced internal sulphate reaction, also referred to in the literature as delayed ettringite formation, DEF). A common requirement for their occurrence is the presence of sufficient moisture inside concrete. By controlling the humidity level in concrete, coatings applied to its surface can help mitigate ASR and DEF, if they have adequate water permeability properties. This paper presents the general criteria that can be used for the selection of polymeric coating materials to protect concrete structures affected by these types of expansive reactions, thus contributing to increase their durability and service life. Moreover, a case study is presented on the performance evaluation of a coating material, selected according to the above criteria and applied to a concrete bridge affected by ASR and DEF.