Phosphate-based treatments for consolidation of salt-bearing Globigerina limestone

Phosphate-based treatments have proven to be effective for consolidation of porous limestone. However, application on salt-laden stone must be evaluated, as salt-weathering is among the main deterioration phenomena for this lithotype and salts present in the stone can interfere with the outcome of consolidation. For this reason, here, the phosphate-based consolidant was tested on a salt-bearing porous limestone (Globigerina limestone). To achieve salt contamination and to induce weathering, stone samples were subjected to crystallization cycles in sodium sulfate, which is among the most common and damaging salts that affect limestone on site. Phase formation and distribution of the consolidant were evaluated in the presence of salts. The treatment efficacy was investigated in comparison with ethyl silicate, which is currently the most used consolidant for porous limestone. Promising results were obtained, indicating that the presence of sodium sulfate does not hamper penetration of the phosphate-based consolidant. By penetrating deeply into the stone and sealing cracks caused by weathering, the consolidant enhances strength and stiffness. Moreover, the presence of salts does not interfere with the formation of calcium phosphates, hydroxyapatite being the only phase to be detected. These results indicate that the phosphate-based treatment is suitable for consolidation of limestone, even when contaminated with salt.