Influence of Hydroxyethylmethyl Cellulose Admixture on the Hydration Process and Mechanical Properties of Modified...

Gypsum is one of the main binding materials used in the construction industry. Its properties can be modified by the addition of chemical admixtures that may influence the hydration process and the microstructure of the hardened material. An important group of such admixtures comprises cellulose ethers. The aim of this study was to conduct an in-depth analysis of the effects of hydroxyethyl methylcellulose (HEMC) on the hydration and mechanical properties of gypsum. HEMC was applied in various amounts (ranging from 0.5 to 7% by mass of gypsum); the water-to-gypsum ratio was 0.75. The hydration process was investigated using calorimetry, thermal analysis, and infrared spectroscopy. Compressive and bending strength tests were also performed. The results of calorimetric measurements show that the presence of HEMC led to delayed hydration and prolonged gypsum crystallization, particularly at higher admixture dosages. No formation of new phases in the gypsum paste was observed in the presence of HEMC. However, the admixture modified the microstructure of the hardened material, as reflected by increased compressive and bending strength. This effect is most likely associated with the slower precipitation of gypsum crystals in the presence of HEMC.