Study and Characterization of Special Gypsum-Based Pastes for Their Use as a Replacement Material in Architectural Restoration and Construction

Within the construction sector, the use of gypsum-based pastes features in the majority of monuments, giving this material significant relevance in conservation and restoration projects affecting the world's cultural heritage. In this research, we evaluated special gypsum-based colored pastes mixed with air lime, hydraulic lime and sodium silicate, and eight different pigments for their use as replacement materials in architectural restoration and construction. We analyzed the suitability of their physical and chemical properties and their hydric characteristics, mechanics and colorimetric implications in two different studies after 28 days and 120 days. The characterization of the products has mainly confirmed the suitability of the pastes containing pigments for use in the most common applications for these kinds of mixes, highlighting that their specific capacities are worth leveraging. The crystallization of gypsum minerals, observed in all of the mixes, helps to consolidate the shrinkage cracks which appear inside the pastes, improving their mechanical strength values. Another observation of the pastes is related to the amorphous silica precipitates in the mixes which contained sodium silicate: the latter provided to them good mechanical behavior. The improvement observed in the pastes containing the green earth pigment is substantial, due to the inclusion of aluminum silicates and Mg, which is partly responsible for the increased compressive strength of the pastes. Finally, the colorimetric analysis is of vital importance in determining the loss of intensity of the colors of the pastes used, since subjective observation leads to serious errors of interpretation.

Automated summary

Gypsum-based pastes are widely used in the construction sector and play a significant role in conserving and restoring the world's cultural heritage. This research evaluated the physical, chemical, and hydraulic properties of special gypsum-based colored pastes mixed with lime and sodium silicate, as well as eight different pigments. The studies analyzed the mechanical characteristics and colorimetric implications of these pastes after 28 and 120 days. The results confirmed the suitability of the pigmented pastes for common applications, with the gypsum mineral crystallization helping to consolidate shrinkage cracks and improve mechanical strength. The inclusion of sodium silicate in the mixes also contributed to good mechanical behavior. The pastes containing green earth pigment showed substantial improvement in compressive strength. Colorimetric analysis proved vital in accurately determining color intensity loss in the pastes.