Mechanical and structural properties of fiber-reinforced heavyweight self-compacting concrete incorporating supplementary cementitious materials

• Rheologically stable FRHWSCC samples based on magnetite and baryte were prepared. • Samples exhibited excellent workability, and self-compatibility. • Magnetite, and steel fibers significantly improved mechanical characteristics. • Steel, CNT, and PP fibers reduced shrinkage, enhancing dimensional stability. The study examines the mechanical, and structural properties of fiber-reinforced heavyweight self-compacting concrete (FRHWSCC) incorporating high-density baryte, and magnetite aggregates. Three types of fibers were utilized: polypropylene (PP), multi-walled carbon nanotubes (CNT), and steel (St), with volumetric contents of 0.5 %, 0.5 %, and 2.0 %, respectively. Two concrete series were designed: S100, and S65. The S100 series comprised 100 mass% ordinary Portland cement (OPC), while in the S65 series, 35 mass% of OPC was substituted with supplementary cementitious materials (SCMs), including ground limestone (GL), ground-granulated blast-furnace slag (GGBFS), and metakaolin (MK). Experimental findings revealed that the compressive strength of magnetite-based samples exceeded 70 MPa, whereas baryte-based samples exceeded 50 MPa after 90 days. Structural evaluations through mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) provided detailed analyses of porosity, and interfacial transition zone (ITZ) between fibers, and concrete matrix. The incorporation of SCMs enhanced long-term mechanical properties through pozzolanic/alkali-activated reactions, and pore structure refinement, thereby densifying the concrete matrix. The addition of PP, and St fibers improved flexural strength, and crack resistance, while all three fiber types contributed to reduced shrinkage.