Effect of Sulfate Ion Environment on Physical and Mechanical Durability of Cement Products Modified by Cellulose Ethers

The object of research is organic additives of methyl hydroxyethyl cellulose of medium and high viscosity, namely, their nature of the effect on the physical and mechanical durability under the destructive influence of various sulfate-ionic media. The need to study the nature of the effect of this additive on resistance to an aggressive environment is also associated mainly with the expansion of the types of building mixtures to create competitive products without losing product quality and to improve the mechanical and rheological properties. In the course of the study, cellulose ethers of medium (17000–23000 mPa∙s) and high (20,000–30,000 mP s) viscosity were used. Additives were added to the cement in the amount of 0.25, 0.5 and 0.75 wt. %. It was found that the introduction of cellulose ether into cement leads to an increase in the normal density of the dough and an extension of the setting time of solutions, in turn, affects the process of strength gain of the latter, in comparison with control samples without additives. With the introduction of the additive, the rate of water separation of the mixtures also significantly decreases, indicating the water-retention capacity of the additive. For the concentration of additives in the amount of 0.25 wt. %. This decrease is 2 times less than for control samples. For a concentration of 0.5–0.75 wt. % Water loss is reduced by 3 times compared to samples without additive. Significant changes also occur during the early strength gain of the samples with an increase in the additive concentration. The destructive effect of an aggressive sulfate medium was determined by the change in compressive strength. With prolonged exposure to an aggressive environment on control and test samples, it is noted that the introduction of this additive of organic origin negatively affects the strength characteristics of cement mixtures with cellulose ethers with an increase in the additive content. The above results indicate the advisability of using cellulose ethers of medium viscosity in dry building mixtures as such, which will provide the necessary storage time for the fluidity of the solution and sufficient strength of the final material.