Due to its rapid setting and hardening, gypsum is used primarily as a binder in the manufacture of gypsum concrete and concrete products. Gypsum is able to bind various fillers well: from sawdust and paper to slag. Products with gypsum binders have a low bulk density of 1,000-1,200 kg/m3. To reduce the bulk density and thermal conductivity of products, gypsum plaster paste is mixed with excess water or blowing agents.
Gypsum concretes have a number of weaknesses that limit their application to a certain extent: insufficient water resistance and a propensity to volumetric deformation that causes warping of reinforced gypsum plaster products and makes their reinforcing elements susceptible to corrosion. These drawbacks can be largely eliminated by introducing lime and hydraulic additives into their composition.
By introducing some polymers into the composition of gypsum concrete, it is possible to significantly increase its water resistance. Polymers make gypsum plaster non-wettable, and hydrophobic plasticizing additives combined with vibration compaction significantly reduce the water/gypsum ratio thus increasing both water resistance and the strength of products.
Gypsum mixed with an aqueous solution of carbamide resin acquires intense properties. The products made from this type of gypsum dried at a temperature of 60-70°C have high strength and excellent water resistance. Wood, reeds, chopped fiberglass, non-woven fiberglass cloth, and glass strands can be used as reinforcing materials.
To reinforce gypsum concrete and gypsum concrete products with metal, it is necessary to first coat the reinforcement with corrosion-resistant varnishes.
Gypsum concretes are manufactured from natural gypsum stone mined in quarries, gypsum and gypsum-containing waste products of the chemical industry, as well as from secondary raw materials — waste gypsum consumables from construction sites and gypsum products obtained during the dismantling and demolition of buildings and structures.
Gypsum concrete is used for manufacture of a wide range of products, most of which we will discuss below. These are artificial stone, gypsum panels, partition boards, architectural details, thermal insulation, and many others.