Improvement of ternary gypsum-based composite resistance to a humid environment

The paper describes the behavior of ternary gypsum-based composites, especially the changes of properties caused by the influence of moisture. The ternary gypsum-based mortar, composed of gypsum, hydrated lime, different types of pozzolan (silica fume, granular blast slag, and brick powder), and standard sand was investigated. Pozzolans in the mixture react with hydraulic lime and form CSH phases in the material. The presence of these phases improves the resistance of gypsum against the moisture. The way of samples' storage affects the development of materials structure and properties of gypsum-based mortars. Therefore, samples were stored in two different environments (laboratory conditions and underwater) for a period of 360 days. The basic physical and mechanical properties of samples stored in the laboratory environment and under the water are compared. The comparison of the TG curves, based on the samples of different ages was carried out. The storage in the water has the most significant impact on the properties of all materials, especially on mechanical properties. While the strength of pure gypsum mortar, stored in the water, decreased significantly, and after one year in the water environment, the samples were nearly destroyed, the samples with pozzolan admixtures revealed the improvement of mechanical properties, when stored in water.