Macroscopic behavior and microstructural analysis of recycled aggregate mortar bars exposed to external sulfate attack

The performance of cementitious materials made with Recycled Concrete Aggregates (RCA) and exposed to sulfate-laden environments is not yet fully understood. There are few studies on this topic, and for a full description of the mechanisms of external sulfate attack (ESA), several influencing parameters should be considered. The replacement of natural aggregates by RCA modifies the physical and chemical properties of the new material and introduces additional variables into the already complex mechanism. The high porosity of RCA contributes to accelerating the sulfate penetration from the surface, while the attached mortar increases the mineral supply that can react with the incoming sulfate. This paper describes a study on the performance of mortars made with RCA exposed to different ESA conditions. Design and exposure parameters include three cement, two specimen sizes, and two sulfate media (soil and solution). Visual inspection and measurements of expansion and weight change were used to determine the performance of the mixes. From a microstructural point of view, thermogravimetric analyses were carried out on samples obtained from the mortar bars after exposure. These results are then used to infer on the thermodynamic and kinetic aspects of ESA progression in recycled mortar. Finally, SEM/EDS analyses were also performed to further describe sulfate penetration and its relationship with cracking. The results show a limited influence of fine recycled aggregate on the mortar performance against ESA and no proportionality to its content.