Evaluation of the physical sulfate attack resistance of lightweight concrete with thermally expanded clay

The phenomenon of physical sulfate attack (PSA) is scarcely studied, particularly in lightweight concrete (LWC) comprising thermally expanded clay aggregate (TECA). The mass change and visual appearance as well as other physical properties, such as the compressive strength, equilibrium density, sorptivity, open porosity, and water conductivity, of the concrete samples were evaluated. Additionally, characterization techniques, such as X-ray fluorescence, X-ray diffraction, and scanning electron microscopy, were employed to identify the formed substances after sulfate exposition. Our results revealed a dual attack, by PSA and the chemical reactions that form the sulfates, in LWC and normal weight concrete (NWC). The higher the TECA content, the lower the compressive strength and the relative PSA resistance. However, with the improvement of cement paste, the aforementioned result was reversed. The relatively closed internal alveolar structure present in TECA did not host sodium sulfate crystals or other substances.