Combined reinforcement mechanism of TEOS-barium oxalate-phosphate composite on weathered sandstone

Abstract Sandstone is one of the main rock types constituting stone-based heritage objects. Due to long-term outdoor exposure, sandstone typically exhibits deterioration such as weathering, surface powdering, and structural weakening. To address these issues, this study developed a reinforcement material composed of tetraethyl orthosilicate (TEOS), barium hydroxide, and oxalic-phosphoric acid. The reinforcement mechanism and microstructure of the material were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The reinforcement applicability was systematically evaluated in terms of appearance, color difference, mechanical strength, and aging resistance. The results demonstrate that TEOS form silica–matrix materials, while barium hydroxide reacts with oxalic/phosphoric acid to form in-situ inorganic salt precipitates of barium oxalate and barium phosphate. The silica gel and inorganic precipitates mutually fill the pore spaces, enhancing the mechanical strength, structural stability, and weathering resistance of the sandstone, while largely preserving the original appearance of the cultural relics.