Silica Fume-Modified Stucco Compositions for Restoration of Stucco Domes in the Bathrooms of Historical Houses

This paper aims to improve the properties of mortar for completing bathroom stucco domes in historical houses, as these domes are considered structural elements exposed to compressive loads and harsh external environmental conditions. The composition of the stucco dome mortar was identified by X-ray diffraction analysis, and the main proportion was lime, followed by gypsum and a small proportion of halite salt. The dome mortar was reconstructed with the same composition, and three types of gypsum were used: alpha and beta gypsum and Kimaksitu 200 with air lime. Amorphous silica (silica fume - silica dust) was added to the samples at ratios of 3-5%. The dimensions of the additive were measured using a transmission electron microscope, which averaged 200 nanometers. All the poured mixtures were evaluated at 1, 7 and 28 days after pouring by examining under a scanning electron microscope to monitor the improvement of the internal structure of the samples. The development and formation of calcium silicate phases were monitored by analyzing the samples after 7 and 28 days after pouring process , using X-ray diffraction. We found that The mortar composition of 55% lime, 40% gypsum and 5% silica fume gave the best results in terms of physical properties such as porosity and improvement of the internal structure in conjunction with the formation of C-S-H gel (Calcium–Silicate–Hydrate) and C-A-S-H Calcium–Alumino–Silicate–Hydrate phases, which was the reason for achieving the best mechanical loading (bending test) for this sample, making it the most compatible for use during the restoration of these stucco domes.