Recycling of waste limestone powders for the cleaner production of epoxy coatings: Fundamental understanding of the mechanical and microstructural properties

Epoxy resins are very well suited for floor coatings, but their ingredients are harmful to the environment. Therefore, their content in coatings should be reduced, e.g. by adding a filler. In this paper, the fundamental understanding of the behavior of epoxy coatings modified with the addition of waste limestone powder was systematically assessed in terms of viscosity, mechanical properties (hardness, tensile strength, flexural strength, pull-off strength) and microstructure (powder distribution in the coating, porosity of the concrete substrate). The replacement ratio with limestone powder ranged from 0% to 29% of the mass of the epoxy resin. The following research methods were used: a flow cup, a Shore D durometer, a tensile and flexural testing machine, a pull-off tester, and a scanning electron microscope (SEM). It was observed that an increasing amount of waste limestone powder in the epoxy resin resulted in an increased viscosity of the liquid coating by 56%, an increased hardness of the cured epoxy coating by 10%, a decreased tensile and flexural strength by 62% and 59%, respectively, and a decreased pull-off strength of the coating by a maximum of 21%. Although the limestone powder caused a large increase in viscosity, the surface of the coating remained even, and the pull-off strength was still well above the standard minimum values. Microstructural analysis showed that most of the waste limestone was sedimented at the bottom of the sample, which resulted in a local increase of hardness. The novelty of the study is the investigation of the effects of replacing part of the epoxy resin and curing agent in epoxy coatings with limestone powder sourced from the production of coarse aggregate in aggregate quarries. Adding limestone powder to the epoxy coating will reduce the content of harmful substances in it, lower its price, and mean that mineral waste is recycled. The paper presents an analysis of the properties of a modified epoxy resin with regards to its use in floor coatings.