New Phosphate-Based Treatments for Carbonate Stone Consolidation and Protection

Carbonate stones on site undergo severe weathering processes, that make consolidation and protection necessary. However, currently available consolidants and protectives are far from being satisfactory when applied to this kind of materials. For this reason, in this thesis an innovative hydroxyapatite-based treatment was developed for limestone consolidation, marble consolidation and marble protection. Firstly, a new treatment protocol was set up for limestone and marble consolidation: solution precursor, concentration and pH, application method and possible additions were investigated to improve the treatment performance. Then, efficacy, compatibility and durability of the treatment were evaluated on these two lithotypes, in comparison with the products currently used for the same aim (ethyl silicate and ammonium oxalate). For marble, the treatment protocol developed in laboratory was also tested on a real historic artefact and on site. Moreover, a surface treatment for protecting marble against acidic rain was formulated, investigating how different parameters (starting solution pH and concentration, organic and inorganic additions) affect the morphology, composition and acid resistance of the treated surface. Excellent results were achieved: hydroxyapatite resulted an effective, compatible and durable consolidant for carbonate stone. Moreover, ethanol addition allowed to obtain a uniform, acid resistant protective hydroxyapatite layer on marble.