Workability, Compressive Strength, and Fire Resistance of Fiber-Reinforced Ultra-High-Performance Concrete Incorporating Recycled Fine Quartz and Bauxite

Ultrahigh-performance concrete (UHPC) is a cementitious material known for its exceptional compressive strength, surpassing 150 MPa. It is composed of fine minerals such as silica, aggregates, and a high cement content. Higher packing density enhances UHPC strength. In this study, two key novelties are explored: 1) the production of UHPC using recycled fine quartz powder and bauxite as aggregate; and 2) the incorporation of fibers to enhance fire resistance and evaluate mechanical performance. To optimize particle packing, the modified Andreasen and Andersen model is employed, using materials, including cement, silica fume, fine aggregate as a bauxite, and recycled fine quartz powder. The study employs a standard concrete curing method to achieve excellent compressive strength, which is a challenging task. The compressive strength of UHPC mixtures with various aggregate to cement ratios at 7 and 28 days is reported. The successful incorporation of recycled fine quartz as a replacement for 15% of cement has been achieved in the production of UHPC concrete. The spread values are also measured and analyzed to assess the workability of UHPC. The findings show that using recycled fine quartz and bauxite, UHPC can be designed to achieve approximately 190 MPa strength with standard curing. To enhance UHPC’s fire resistance, this research incorporates polypropylene (PP) fibers. Six UHPC mixtures are designed and tested following exposure to elevated temperatures at 400°C and 725°C. The results indicate that a volume fraction of 0.2% of PP fiber is sufficient to render UHPC fire-resistant, preventing spalling. Subsequently, steel fibers are also introduced to study the properties of fiber-reinforced UHPC in terms of compressive strength and workability. The findings confirm that sustainable and fire-resistant UHPC can be developed using recycled fine quartz and alternative materials.