Conservation of the weathered bricks in ancient constructions using a novel protectant of calcium hydroxy glycolate

Bricks are widely used in ancient constructions throughout the world. However, weathering patterns such as cracking, flaking, and powdering are common among them and conservation interventions are thus necessary. In this paper, the alcoholic solution of calcium hydroxy glycolate was investigated as a novel protectant. It features good penetration and controllability. The consolidation of the bricks can be achieved by successively introducing the alcoholic solution of calcium hydroxy glycolate and water. The consolidation mechanism was studied by scanning electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis. The protection effect was evaluated by determination of penetration depth, water absorption, porosity, water vapor permeability, mechanical strength, and color change. The results show that the consolidation is due to the reaction of calcium hydroxy glycolate with carbon dioxide in the air and active silicon in the brick (25 °C, RH = 60%, 1 atm). The cohesive calcite and calcium silicate phases are thus generated and weathering fragments are reunited together. After treatment, the mechanical strength and weathering resistance of the samples are improved greatly. The porosity, water absorption, and color, however, are affected insignificantly, indicating good compatibility. These satisfying results suggest a promising application prospect of the proposed method in the conservation of heritage brick constructions.