Utilization of waste carbon spheres in magnesium oxychloride cement

The Portland cement (PC) industry is a big producer of CO2 – a major contributor to the global warming. As the world tends to reduce the CO2 emissions because of its negative effect, a sustainable and efficient PC alternative is needed to be found. One of the most promising substitute is based on reactive magnesia – magnesium oxychloride cement (MOC). This paper deals with the design, development, and characterization of environmentally friendly composites based on MOC. In addition to the standard quartz sand filler, carbon spheres-based waste produced by polypropylene treatment via plasma gasification was used as a nanoadditive. Before the preparation of the composites themselves, the carbon spheres (CS) were analysed with a wide range of analytical methods in order to determine their microstructure and composition. The CS were used in the amount of 0.5, 1.0, and 3.0 wt.% related to the weight of the pure MOC paste. The prepared composite samples were tested for their microstructure, phase and chemical composition, micro- and macrostructural parameters, and mechanical properties after 28 days of maturing. Furthermore, the influence of CS on the hygric properties and the water resistance of the MOC-based composites were studied after 24 h-long immersion in water. It has been shown, that with the increasing amount of CS, the mechanical parameters improve quite rapidly, making CS an enhancing eco-friendly nanoadditive. It was also shown, that CS helps to slow down water transport in MOC-based composites, which is a key aspect in the improvement of their water resistance and overall durability after exposure to humidity. The incorporation of carbon spheres-based waste as a nanoadditive in MOC-based composites shows promising improvements in mechanical properties and water resistance, contributing to the development of environmentally friendly construction materials.