PSI - Issue 54

João Custódio et al. / Procedia Structural Integrity 54 (2024) 271–278 João Custódio et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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In existing structures, there is a limited number of ways in which this can be achieved; furthermore, the type of structure and structural elements affected by ASR, as well as the environmental service conditions, to which the structure is exposed to, will also condition the solution than can be adopted and the level of ASR suppression that can be achieved. One of the ways to control humidity inside the concrete is by using surface protection systems. These systems have the potential to mitigate ASR and DEF since they can act as a barrier against the entry of water or allow concrete to dry while limiting water ingress, if they have adequate water vapour permeability properties. However, there is a wide range of surface protection systems available on the market, with very different properties that may or may not be suitable for mitigating the internal expansive chemical reactions; thus, proper selection of a surface protection system, considering factors such as barrier properties, is critical to ensure that it effectively mitigates the reactions within a structure. Currently, there are no standards providing specific guidance on the selection and acceptance of suitable surface protection systems to prevent or mitigate these reactions in structures. This communication presents the general criteria that may be used in the selection of surface protection systems for application in concrete structures affected by ASR and DEF. It also presents the preliminary results of a case study in which the internal relative humidity of the concrete, of a structure affected by expansive reactions, is periodically monitored, after the application of a polymeric coating that was selected based on the above criteria. 2. Coating system selection The European Standard EN 1504 series “Products and Systems for the Protection and Repair of Concrete”, in its 10 parts, proposes various methods for the protection and repair of concrete, defines the characteristics to be evaluated and establishes the respective minimum requirements. Part 9 of EN 1504 series systematises the main deterioration mechanisms of concrete structures, namely the physical, chemical, or mechanical deterioration processes of the concrete itself and the corrosion processes of reinforcements. This standard also defines the chemical, electrochemical and physical principles of protection and repair that can be used to prevent or stabilise the deterioration of concrete structures, such as, P1 – Protection against ingress; P2 – Moisture control; P3 – Concrete restoration; P4 – Structural strengthening; P5 – Increasing physical resistance; P6 – Resistance to chemicals; P7 – Preserving or restoring passivity; P8 – Increase Resistivity; P9 – Cathodic control; P10 – Cathodic protection; P11 – Control of anodic areas. The first six principles of protection and repair are related to the deterioration of concrete and the remaining five are related to reinforcement corrosion. These “principles” are directly related to the actions from which the concrete is intended to be protected. According to Parts 9 and 2 of EN 1504, surface protection systems are used as “methods” for the protection and repair of concrete structures for the following five protection “principles”: P1 , P2, P5, P6 and P8. The selection of a surface protection system is based on an assessment of the causes of deterioration and on the consideration of the appropriate principles according to which it should act. Part 2 of EN 1504 specifies the type of surface protective methods applicable, lists the performance characteristics of surface protection products and systems to be evaluated for each “principle”, provides the test methods and establishes the corresponding requirements. For preventing or mitigating ASR and DEF, in concrete structures, Principle P2 (Moisture control) applies. The standard enumerates several methods based on this principle, e.g., hydrophobic impregnation, impregnation, coating, cladding. The type of structure and environmental conditions will determine the best solution. The case study addressed in this paper consists of a bridge affected by ASR and DEF. Due to its characteristics and the service environment it was found that the most feasible surface protective method consisted of a coating, i.e., a treatment to produce a continuous protective layer on the surface of concrete. There is a wide range of coating products and systems available on the market which, within a similar family or type of binder, can have very different properties and thus result in different levels of protection. Therefore, when selecting a coating system , and in the absence of a history of satisfactory field performance, its performance must be evaluated. Part 2 of EN 1504 specifies the mandatory performance characteristics to be considered in the selection process and the respective requirements to be met by the coating system. These are summarised in Table 2. Although, the mandatory characteristics focuses on barrier properties, for a coating system to effectively mitigate ASR and DEF it must also be evaluated for other characteristics, e.g., crack bridging ability, durability. In addition, the values of the requirements, given in Part 2 of EN 1504, for the abovementioned characteristics, do not guarantee per se that the coating will effectively mitigate ASR and DEF in all environmental service conditions. Although, they