Pressure-molded gypsum plaster: the effects of forming parameters on physical and mechanical properties

ABSTRACT

The low mechanical strength and susceptibility to water restrict the application of gypsum plaster in non-structural elements and places protected from moisture. On the other hand, pressure-formed gypsum plaster has been pointed out as an alternative to obtaining high performance plaster pieces. However, the influence of processing and mixing-related factors on the properties of pressure-formed gypsum plaster pastes has yet to be discovered. This article aims to investigate the effects of pressure (P), formed mass (M), and water/gypsum ratio (X) on the physical and mechanical properties of pressure-molded gypsum plaster (PMG). A 2^k factorial design was used to evaluate the effects of these forming factors and their interactions. In this project, P varied from 5 to 15 MPa, M from 350 to 550 g, and X from 0.18 to 0.22. Thickness (t), porosity (η), dynamic modulus of elasticity (E), flexural tensile strength (S_t), and compressive strength (S_c) of prismatic specimens were the analyzed properties. The results showed that the pressure and the water/plaster ratio had significant effects on all properties except thickness, and the formed mass affected only the specimens’ thickness. Plaster molding under pressure proved to be a promising technique for developing plaster pastes with high mechanical performance (E = 20.0 GPa, S_t= 12.6 MPa, and S_c= 53.5 MPa) and low porosity (η= 20.1%). The results indicated the need for a retarder to guarantee the plaster compaction before the setting and to improve the dihydrate crystals packaging. The press-forming technique proved suitable for developing prefabricated gypsum components with high mechanical strength for civil construction.

Keywords
Pressure-molded gypsum plaster; 2^k factorial design; Porosity; High-strength gypsum plaster