STUDY OF THE IMPACT OF SURFACTANTS ON THE STRUCTURE FORMATION OF HYDRATED GYPSUM BINDER

Abstract

Relevance. Ukrainian and foreign researches consider gypsum the most effective material due to its peculiar properties. You can hardly find a material like this that would have the same characteristics, sustainability, and ensure adequate standard of living. The production of building materials based on gypsum binders is not associated with hazardous wastes and emissions and does not cause negative environmental impacts. Besides, the manufacture of gypsum binders requires 3…5 times less energy compared to lime and cement. These advantages encourage researchers to proceed with further attempts to obtain a gypsum structure exhibiting the properties of cement binders. One of the trends involving the formation of this kind of structure is studying the impact of additives on the hydration process. The use of plasticizers is of particular interest in this research area. Problem statement. Structure formation process generally depends on the initial content of binding substances and substances interacting during the hydration process. The analysis of technical publications shows that production of composite binders is a priority in the manufacture of mineral binders. A second priority is the use of various additives and factors affecting the hydration process. Most studies using additives involve the structuring of gypsum- and cement-based materials in order to improve physical and mechanical properties. The literature review conducted shows that there is insufficient information on the hydration process mechanism and impact of plasticizers on the structure formation of mineral binders. The purpose of the article. Assessing the effects of surfactants on the mechanism of structure formation and hydration processes in gypsum binders. Conclusion. The studies conducted helped to identify the effects of surfactants on the structure and properties of hydrated gypsum binder; furthermore, the most effective additives were identified, allowing to reduce water-togypsum ratio significantly, improve strength values, and obtain a binder with a higher density structure. If crystals are grown using СаСІ2 + Nа2SO4 + 2Н2O → СаSО4 ∙ 2Н2О + 2NaCl solution, gypsum specimens will have a high-porosity fibrous microstructure. During counterdiffusion growth of gypsum crystals in the presence of surfactants, filling of interlayer voids can be observed in the microphotographs. Crystals begin to grow from one point, which is due to changes in surface tension. The studies have revealed that plasticizers promote the growth of crystals and the surface energy can be modified depending on the type of additive, which can affect the hardened binder structure. The best results have been achieved with Sika and ACE 430 plasticizers. The X-ray diffraction analysis of the produced СаSО4 ∙ 2Н2О crystals has shown that binder hydration process intensity is related to the impact of additives on the shape and size of calcium sulfate crystals and calcium sulfate dihydrate and depends on facial surface energy.