Abstract
The study is focused on the influence of a water-soluble polymer (in weight fraction up to 1.5%), cellulose derivatives—hydroxyethyl methyl cellulose, on gypsum properties. Gypsum setting involves two processes: gypsum hydration/crystallization and probably formation of a polymer film in material pores. The processes are studied by various methods such as setting time and mechanical measurements, scanning electron microscopy and differential scanning calorimetry. The additive acts as a retarder (an increase in setting time), and it modifies the morphology of calcium sulfate dihydrate crystals, leading to the change in mechanical properties—an increase in bending stress. The mechanism of gypsum crystal growth during hemihydrate hydration is predicted to be a nucleation control process (the Avrami equation is applied). The value of nucleation rate constant decreases with an increasing additive content.
Highlights
In recent years, interest in modification of building materials such as gypsum or cement by mixing with polymers has been observed
The following samples were prepared to use in calorimetric, setting time and mechanical studies: gypsum without admixtures and gypsum with various Hydroxyethyl methyl cellulose (HEMC) contents (0.25–1.5%)
The addition of a small amount of HEMC admixture caused an insignificant prolongation of the setting and induction time
Summary
Interest in modification of building materials such as gypsum or cement by mixing with polymers has been observed. The following samples were prepared to use in calorimetric, setting time and mechanical studies: gypsum without admixtures and gypsum with various HEMC contents (0.25–1.5%). Samples of gypsum plasters with initially various water-togypsum ratios which contained HEMC admixtures in weight fractions from 0.25 to 1.5% were prepared.
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