Ultra-high-performance concrete (UHPC) is a crucial material in modern infrastructure, prized for its exceptional compressive strength (exceeding 150 MPa), high durability, and unique composition. UHPC is made up of aggregates and fine minerals like silica, with a high cement content. This study examines the mix design and properties of UHPC, with a focus on enhancing its mechanical strength through optimized particle packing density using the modified Andreasen & Andersen (MAA) particle packing model. The goal is to maximize the packing density in UHPC by replacing silica fume (SF) and part of the cement with recycled fine quartz powder, a high-purity microsand derived from Caesar Stone quartz slurry waste. Recycled fine quartz (RFQ), with particle sizes averaging 15 μm, can provide environmental benefits and industrial applications as a microfiller, partially replacing cement and silica fume. The UHPC-35RFQ mixtures are cured using a standard method to achieve high compressive strengths of around 170.1 MPa at 28 days and an impressive early strength of 141.6 MPa at 7 days. The spread value and air content are measured to assess the workability of UHPC, with results showing a notable 31% increase in overall workability compared to UHPC-SF mixtures. Replacing SF with RFQ results in a 3.1% increase in compressive strength at 7 days, although compressive strength decreases by 9.6% at 28 days. These differences are small and can be attributed to the microfiller effect, which is stronger in early-age UHPC containing recycled quartz, and the high pozzolanic activity of silica fume, which becomes beneficial at a mature age. Replacing all silica fume content, amounting to 20% of cement weight, with recycled fine quartz in UHPC has proven cost-effective.