Conference, Proceedings

Flue gas desulfurization gypsum and gypsum from chemical production is produced in high
amounts. However, the industrial use of gypsum is insufficient considering the amount of its
production. Nowadays, it is mostly used for the production of gypsum plasterboards only, and
the rest is deposited at waste disposal sites. Due to the very low price and large availability of
waste gypsum, the material has a good potential for applications in buildings not only for
dividing structures as with the most current gypsum applications but in some cases also for
load‐bearing structures. One of the reasons for the neglect of the material by building industry
is the almost complete lack of knowledge of its properties.
For an extended use of gypsum in buildings some modifications of this material are necessary
which are supposed to enhance its original properties and increase its service life. For instance,
use of plasticizers or fiber reinforcement can increase the mechanical strength of gypsum
products, hydrophobization can protect the material from water penetration, fillers can
decrease the necessary amount of binder in a composite material.
Modifications of gypsum are usually performed using polymer materials. Bijen and van der
Plas [1] reinforced gypsum by E‐glass fibres, and modified the binder by using acrylic
dispersion in a mixture with melamine. The results showed that this material had higher
flexural strength and higher toughness than glass fiber reinforced concrete after 28 days. A
disadvantage of polymers based on carbon chain is a decrease of fire resistance of calcined
gypsum elements. Application of hydrophobization admixtures is another way of possible and
perspective gypsum modification because the resistance of hardened gypsum against water is
still considered a serious problem. In the literature, only applications of lime and artificial resins
(polyvinylacetate, urea formaldehyde and melamine formaldehyde) were studied, some
inorganic substances such as fluorosilicates, sulfates and silicates were found to increase
hardness and impermeability of the surface, see [12]. Colak [2] impregnated the gypsum
surface by various epoxy resins and studied the effect of impregnation on mechanical
properties and water sorption. While the flexural strength was not changed due to the
impregnation, some resins were found to protect gypsum completely from water penetration.
However, generally it can be stated that the resistance of hardened gypsum against water is not
yet resolved in a satisfactory way.
The primary aim of our research work is the adjustment of basic technologies for the production
of modified gypsum, particularly from the points of view of hydrophobization and
improvement of mechanical and thermal properties.
Very few information about material properties of gypsum products was published until now.
Basic mechanical properties of calcined gypsum (compressive strength, tensile and flexural
strength, Youngʹs modulus, Poisson constant) are relatively well known, see, e.g. Klein and
Ruffer [7], Singh and Garg [13], Tazawa [15]. Thermal properties of calcined gypsum (thermal
conductivity, specific heat, thermal diffusivity) were determined for instance in Danten et al.
[5], Mehaffey [10] and Hanush [6]. Among the hydric properties of calcined gypsum,
Hanusch [6] introduced the water vapor diffusion resistance factor, Dahl et al. [4]
measured sorption and desorption isotherms, Lucas [9] the sorptivity. However, the
data sets presented by various investigators for different types of calcined gypsum are mostly
incomplete so that their applicability is limited. Complete sets of thermal, hygric and
mechanical parameters of practically any type of non‐modified and modified gypsum are very
rarely available and without their knowledge it is impossible to perform any serious mechanical
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