Research of structure and durability of natural polymer modified clays

Abstract

The issue of eco-friendly construction is highly relevant nowadays. Unfired clay materials represent a sustainable alternative to other building products, because of their extremely low carbon footprint. Nevertheless, a pressing need remains to enhance their physical, mechanical, and durability characteristics. To save the great ecological potential of unfired clay materials, the most rational way is to modify them with the help of different biopolymers. Therefore, the dissertation considers the possibilities of different biopolymers (polysaccharides – starch, alginate, and chitosan) to modify clay-based building materials. Different preparation technologies (biopolymers gelation and starch retrogradation processes) were used to evaluate the effect of the examined biopolymers on some properties, structure, and durability of clay materials. Biopolymers and their technological parameters were selected according to their origin, chemical structure, and ability to interact with water. The main principle of clay modification, implemented in this research is the complete replacement of water with a biopolymer solution during the manufacturing process of clay composites. The resulting clay composites with starch or alginate solutions exhibit not only improving mechanical properties but also durability, which could make them very attractive for a wide variety of applications from clay masonry units to plasters. The first chapter presents a comprehensive outlook on contemporary trends in the evolution of sustainable clay-based construction materials. Furthermore, it delves into an exploration of the biopolymers, their distinctive characteristics, and the potential avenues for modification. The second chapter is dedicated to the exploration of the raw materials, processing techniques, testing methodologies and equipment used to evaluate the impact of biopolymers on unfired clay composites. The discussion has also focused on the technology of producing gelated biopolymer aqueous solutions, and the possibilities to technologically modify specific biopolymers using the retrogradation process. Also, this chapter presents the methodology of clay composite testing. The third chapter presents the evaluation of the effect biopolymers have on the physical, mechanical, and hygroscopic properties and durability of clay-based composites, describing interaction mechanisms between clay and biopolymers, and the peculiarities of clay composite structure formation. Nine scientific papers were published on the topic of the dissertation: three papers in scientific journals included in the list of Clarivate Analytics Web of Science database with an impact factor, and four papers in conference proceedings included in the Clarivate Analytics Web of Science and Scopus databases, two – in other international databases. A Lithuanian patent based on the results of the dissertation has been granted, and seven reports were presented at national and international scientific conferences.