Influence of Aggregate Type and SCM Combinations on the Fresh and Mechanical Properties of Ultra-High Performance Concrete

To improve sustainability and reduce the production costs of ultra-high performance concrete (UHPC), the use of locally available aggregates is highly desirable. The combined impact of aggregate type and different supplementary cementitious materials (SCMs) on the fresh and mechanical properties of UHPC is not yet sufficiently understood. Therefore, quartz, limestone, and diabase aggregates together with different SCM combinations were used in the experimental investigation of eighteen UHPC mixtures. Laboratory tests, including flow table, compressive strength, and flexural strength tests, were performed to evaluate the performance of the mixtures. Mixtures containing limestone and fly ash (FA) generally showed higher workability compared to those containing metakaolin (MK). The highest compressive strengths were achieved in mixtures with quartz sand (average 110 MPa) containing approximately 20% MK relative to the total binder content. The mixture with optimal particle distribution and the lowest cement content (500 kg/m³) also showed extremely high mechanical performance. Based on the obtained flexural-to-compressive strength ratios (f_b/f_c), the expression f_c ≈ 7·f_b was proposed to estimate the compressive strength of similar fiber-free UHPC mixtures. Furthermore, heat-treated specimens exhibited a 45% higher compressive strength after 7 days compared to the reference mixture, while the addition of polyvinyl alcohol (PVA) fibers caused a slight decrease in compressive strength of approximately 4%. The obtained results contribute to the development of mechanically efficient UHPC mixtures with optimized particle packing and reduced cement consumption, which may improve the sustainability of UHPC production.