Abstract
Ultra-high performance concrete (UHPC) exhibits exceptional strength and durability; however, its use in stiffness-critical structures is often limited by an elastic modulus that is disproportionately low relative to its compressive strength. To address this limitation, this study investigates the partial and full replacement of conventional fine aggregates (e.g., quartz and river sand) with iron sand. A systematic investigation of the fresh, mechanical, and microstructural properties of iron sand–based UHPC is conducted, with a particular focus on elastic modulus, providing insights into the mechanisms underlying its enhanced performance.The results indicate that incorporating iron sand improves workability, with fluidity peaking at 100% substitution. Mechanically, full substitution increased the 28-day compressive strength and static elastic modulus by 8.6% and 4.9%, respectively. Microstructural analyses revealed a denser and more coherent interfacial transition zone (ITZ) around iron sand particles, in contrast to the microcracking observed at quartz sand interfaces. This microstructural refinement was further corroborated by mercury intrusion porosimetry (MIP), which demonstrated reduced total porosity and an increased proportion of gel micropores. These enhancements underpin the mechanical improvements and align with the consistently low water absorption (<1%) across all mixes.
The spherical morphology and smooth surface of iron sand promote denser particle packing and improved workability, while its high intrinsic stiffness directly contributes to an enhanced macroscopic elastic modulus. The dense ITZ and refined pore structure further facilitate efficient load transfer and enhance durability. In conclusion, iron sand emerges as a technically effective and industrially viable fine aggregate for producing high-modulus UHPC, making it particularly suitable for long-span bridges, vibration-sensitive platforms, and other structures requiring high stiffness and superior durability.
| Date of Award | 15 Jul 2026 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Juan Wang (Supervisor), Weizhuo Shi (Supervisor) & El Said M.M. Zahran (Supervisor) |