Fiber-Reinforced Alkali-Activated Cements from Ceramic Waste and Ladle Furnace Slag without Thermal Curing

Alkaline-activated cement, as an alternative to conventional portland cement, is being increasingly studied due to its environmental advantages and engineering properties. However, research on the feasibility of using both uncommon precursors and curing at ambient temperature is still limited. This study aims to investigate the potential of ceramic wastes, specifically from brick and tile production and ladle furnace slag, as precursors in alkaline activated cement reinforced with polyacrylonitrile fibers cured at 20°C. Sodium silicate, in solution form, was used to activate the precursors, and three different fiber contents were tested, namely 0%, 0.5%, and 1%, by volume. Physical properties, such as capillarity and porosity, were assessed. Moreover, the mechanical behavior was thoroughly characterized by uniaxial compressive, flexural, and elasticity modulus tests. In addition, a thorough microstructural characterization, including scanning electron microscopy, X-ray energy dispersive analyzer, X-ray diffraction, and Fourier transform infrared spectroscopy was conducted at 14, 28, and 90 days. The results revealed that environmentally friendly alkali-activated binders were produced from wastes with limited industrial recycling possibilities. The mixture with 0.5% fibers was the one that presented better results, i.e., a flexural strength of $8.84\mathrm{N}/{\mathrm{mm}}^2$ and compressive strength of $\sim 29\mathrm{MPa}$ at 90 days. The mechanical performance of this material is relevant, especially considering that a relatively low curing temperature was applied. The results also showed that calcium aluminum silicate hydrate (C-A-S-H) was detected as the main reaction product.

Alkali-activated cement has been identified as a potential alternative to traditional portland cement due to advantages such as the reduction of ${\mathrm{CO}}_2$ emissions to the atmosphere, and the conservation of natural resources, because wastes can be transformed into useful products. All over the world, ceramic materials are widely used in different types of construction, and significant amount (between 30% and 45%), end up as waste. Therefore, this study aims to show the possibility of reusing ceramic waste for the development of a fiber-reinforced alkaline activated cement composite with acceptable physical and mechanical properties that allow it to be used in non-structural applications; for example, bricks, tiles, partition walls, and other building materials. It also is a low-energy consumption process, because curing can be done at ambient temperatures. Finally, the obtained results, e.g., flexural strength of $8.84\mathrm{N}/{\mathrm{mm}}^2$ and compressive strength of 29 MPa, open the door for several applications in the construction industry.