## 1 Introduction  
The evaluation of the mechanical behaviour of concrete is always considered essential, while the evaluation of the durability of this construction material is sometimes overlooked. Concrete with high porosity allows the entry of external agents, which can lead to durability problems; hence, it is essential to study in detail several properties that are related to the durability of concrete. The permeability to aggressive agents in concrete can be measured through several tests, such as evaluating the transport mechanisms associated with chloride ions, oxygen and carbon dioxide. The analysis of the permeability of concrete to gases concerns the entire porous structure of this material, i.e., both small and large pores, due to the reduced size of the oxygen molecules. Therefore, the oxygen permeability test has a higher sensitivity than the water absorption tests, since the water molecules are larger than the oxygen ones [1]. The transport mechanism of chloride ions in concrete is somewhat complex, and may involve diffusion, impregnation and capillary water absorption processes. Transport mechanisms vary widely with the microenvironment in which the structural elements are inserted. The penetration of chlorides into ordinary concrete is usually carried out through the continuous pore structure of the cementitious paste, the interface between the aggregates, and the paste (ITZ) and micro-cracks [2]. The penetration of chlorides is, together with carbonation, the main factor responsible for the depassivation and corrosion of steel reinforcement in reinforced concrete. In turn, the carbonation process begins with the penetration, by diffusion, of carbon dioxide (CO\({}_{2}\)) into concrete, which, in the presence of moisture, reacts with the hydrated cement minerals and gives rise to carbonation. In other words, CO\({}_{2}\) in the atmosphere reacts with the alkaline components of concrete, namely by transforming calcium hydroxide (CH) into calcium carbonate. These chemical reactions of dissolution of the crystalline phases of concrete cause a decrease in the pH of the concrete pores' solution, enabling the corrosion of the steel reinforcement, since the oxide film that protects the steel reinforcement is only stable in very alkaline environments [3]. The carbonation resistance of concrete is generally determined through accelerated tests, in which the concrete specimens are subjected to high concentrations of CO\({}_{2}\) (5%). Thus, one of the problems of this type of test is to understand whether the results obtained evaluate rigorously the behaviour of concrete exposed to atmospheric CO\({}_{2}\) concentrations. It is recalled that the concentration, in volume, of CO\({}_{2}\) in the atmosphere usually varies between 0.03%, in rural areas, and 0.10%, in places with high population density [4]. According to data presented by the United Nations, in 2015 the world population was around 7.3 billion, and this number is expected to reach 9.7 billion in 2050 [5]. That report also indicates that, in 2015, for the first time, the majority of the world's population already lived in cities. The migration of populations to urbanized areas brings benefits for global development, but also implies a significant increase in built parks, with an increase in the production of construction and demolition waste (CDW), whose environmental impact is extremely negative. Although the use of CDW already occurs, as aggregates in concrete in some constructions, the truth is that its incorporation still corresponds to occasional cases and it is not a common reality. The use of recycled aggregates (RA) in concrete raises some important questions in terms of durability. These aggregates have physical properties and compositions that are very different from those of natural aggregates. The main difference is related to the greater porosity and, consequently, greater water absorption of RA. However, this variation depends on the RA's source and production process.