Consolidation of building materials with a phosphate-based treatment: Effects on the microstructure and on the 3D pore network

Highlights: • DAP solutions react with carbonatic stones and form phosphate phases on pore walls. • The crystallization of new phases modifies the water absorption by capillarity. • DAP treatments reduce the total open porosity and modify the pore size distribution. • MIP and SR-μCT are compared to study the 3D pore network of porous stone materials. • 3D microstructural features of treated stone are explored by a new multiscale approach. -- Abstract: Inorganic-mineral treatments are commonly applied to decayed stone substrates in order to slow down the decay processes, through the partial transformation of the original stone material into newly-formed crystalline phases. The purpose of this study is to explore the effects induced by a promising consolidating treatment based on diammonium hydrogenphosphate (DAP) solutions on Noto limestone, a porous carbonatic matrix used as ornamental stone in the south of Italy. The research findings, obtained combining water absorption by capillarity measurements, mercury intrusion porosimetry (MIP) and synchrotron radiation X-ray micro-computed tomography (SR-μCT), demonstrate that the DAP consolidation induces microstructural modifications of the stone in terms of porosity and pore size distribution, changing the capillarity absorption values and decreasing the sorptivity speed. This study paves the way to a deeper investigation of the effects induced by a wider range of conservation treatments to the 3D microstructural features of porous geomaterials, by using an innovative multi-scale approach.