## 3 Results and Discussion
### Durability Properties  
To determine the chloride ion diffusion coefficient in the studied concretes, the procedures established by [34] were followed. In this test, chloride ion penetration occurred in a single direction, from bottom to top, driven by the passage of electric current. Figure 17 shows the concrete specimens after the test and the application of silver nitrate (AgNO\({}_{3}\)) spray to define the chloride ion penetration depth. Qualitative evaluation showed that the SCLC-SMR37 mix exhibited the smallest chloride ion penetration front, followed by SCLC-EC, SCLC-SBA50, and finally SCLC-SBA90, which showed the greatest penetration depth. However, it was noted that the aggregates in the SCLC-SMR37 mix floated within the paste and deposited on the top part of the specimen, resulting in segregation between the cementitious matrix and the aggregates. This behaviour can be explained by the low absorption and relatively low density of the SMR37 aggregate, making it difficult to homogenize with the paste as it requires more time to absorb the mixture. Figure 16: Efficiency factors of the SCLCs. Due to the behaviour exhibited by the SMR37 aggregate, in accordance with the normative specifications of [34], the chloride ion diffusion coefficient for SCLC-SMR37 was disregarded as it did not represent the proper behaviour of the mix. Figure 18 presents the chloride ion diffusion coefficients for the self-compacting lightweight concretes at 186 days, after being subjected to wet and air curing. From the obtained results, a relationship between the diffusion coefficient and the mortar content of each mix can be observed, as per the data in Table 5. It is noted that the mixes with lower diffusion coefficients, except for SCLC-SMR37, had higher mortar contents. According to [PERSON] and [PERSON] [19] and [PERSON] and [PERSON] [23], the presence of porous aggregates contributes to increased permeability in concretes. However, a higher mortar content produces a denser cementitious matrix, reducing permeability by improving the matrix's pore structure, thus enhancing durability performance. Additionally, there is microstructural improvement due to internal curing provided by the water retained by the lightweight aggregate, which refines the aggregate-matrix interface, reducing microcracks typically found in concretes with conventional aggregates. These microcracks are the main pathways for aggressive agents to percolate. Figure 17: SCLC specimens after silver nitrate (AgNO\({}_{3}\)) spray. Figure 18: Chloride ion diffusion coefficients in the SCLCs. [PERSON] et al. [37] reported that lightweight aggregate itself does not influence the determination of the diffusion coefficient, indicating no clear relationship between aggregate porosity and the diffusion coefficient. However, other factors such as matrix quality, w/c ratio, binder content, and especially pre-saturation of high-absorption aggregates can affect the concrete's resistance to chloride ion penetration. It is recommended to avoid saturating the aggregates to reduce their contribution to chloride penetration. As observed in the study and discussed by other authors [19; 23; 38], this may have occurred due to the low mortar content in the mixture, as well as the higher proportion ratio between coarse aggregate and mortar (Vg/Vm). Alternatively, as [PERSON] et al. [37] found in their study, although lightweight aggregate alone does not influence the determination of the diffusion coefficient, lightweight aggregates with high absorption levels can influence the resistance of concrete to the entry of chloride ions. However, when comparing CLAA-RBC50 (25% absorption) with CLAA-RBC90 (15% absorption), we observed that the diffusion coefficient of CLAA-RBC50 was lower, even though it had the aggregate with the highest absorption.