The Production of Gypsum Materials with Recycled Citrogypsum Using Semi-Dry Pressing Technology

Abstract

The search for ways to utilize and recycle industrial by-products is the basic principle that governs rational environmental management, synthesis of “green” materials, and appears as one of the main criteria for sustainable development in most countries of the world. Gypsum-containing waste (GCW) derived from industries, represents a large-tonnage product. The production of gypsum materials could be one of the ways to recycle GCW products. GCW from various industries can be used as an alternative to natural raw materials when producing gypsum binders. However, the features of GCW do not allow the production of a high-quality binder when traditional technologies are applied, so it requires the development of additional methods or the introduction of various modifiers to the binder system. One of the ways to increase the efficiency of GCW as a raw material for the production of gypsum binders is to apply a semi-dry pressing method, at reduced values of the W/S ratio of the binder. The objective of this research was to study the possibility of increasing the efficiency of GCW using citrogypsum for production of gypsum materials, by optimization of the mix design and by applying a semi-dry pressing method, using a lower pressure load at the molding stage. The mix design and technological parameters were optimized using mathematical planning of the experimental method. Parameters such as the amount of citrogypsum as an additive in the raw mixture, molding pressure, and water–solid (W/S) ratio were taken as input parameters of variation. To plot the relationship of the input–output parameters, the SigmaPlot software was applied, to analyze and demonstrate scientific and statistical data in the form of nomograms. It has been established that the use of the semi-dry pressing method with the optimal mix design and technological parameters, makes it possible to obtain gypsum samples with demolding strengths up to 2 MPa, and final compressive strengths up to 26 MPa. The incorporation of citrogypsum and the optimal W/S ratio of 0.25, results in positive effects, such as a reduction in the sticking properties of the mix during the demolding stage, and the homogeneity of compaction and visual appearance of the samples were also improved.