Abstract
The conservation of weathered historic sandstone with apatite was studied. Based on the growth mechanism of bone, calcium and phosphorus were introduced into weathered sandstone and then mineralized at room temperature. The conservation efficiency was investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), and compressive strength, capillary water uptake, water vapor permeability and weather resistance tests. The SEM, EDX, TEM, SAED and XRD results showed that the produced hydroxyapatite could reunite the weathered stone blocks and provide sufficient reinforcement to hold them together. The results of the various tests indicated that the compressive strength and weather resistance of the treated samples was improved significantly. In addition, because of the porous nature of apatite, the water vapor permeability of the treated stone was not affected and its breathability was maintained.
Highlights
The conservation of weathered historic sandstone with apatite was studied
Lime hydrate was prepared as follows: calcium oxide powder was added to distilled water with agitation and the slaking temperature was held at 80±10°C
The conservation efficiency of the consolidant was estimated by compressive strength, capillary water uptake, water vapor permeability and weather resistance tests
Summary
A. R. grade calcium oxide (CaO), Vaseline, 1-propanol and ammonium phosphate ((NH4)3PO4) were used without further purification. The simulated test blocks of weathered moderate-grain sandstone (cylinders that were 3.0 cm high and 5.0 cm in diameter) were made according to a method described in the literature [26]. An evenly blended mixture of CaCO3 powder (5 g), mid sand (45 g) and deionized water (6.0 mL) were added into a cylinder shaped mold, and a hammer was dropped 12 times from a height of 277 mm to compress the sample. The obtained test blocks were stored at 25°C and 60 5% humidity for 7 d prior to use
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