Aggregate packing characteristics dependent fresh and hardened properties of steel fiber reinforced lining segment concrete

The performance of lining segment concrete is one of the key factors affecting the service performance of shield tunneling. This study investigates the fresh and hardened performance of steel fiber-reinforced concrete for large-diameter (15 m) shield tunnel segments, with a particular focus on the influences of packing characteristics of different aggregate-steel fiber systems. The flowability of fresh segment concrete under static and vibration was analyzed by excess mortar and aggregate inter-fraction. And the pore structure and fiber distribution were quantified to clarify their effects on its compressive, flexural strength and chloride resistance. The results indicated that the deformation of fresh segment concrete under self-gravity increased with improving particle packing density and excess mortar volume, while its flowability under vibration was predominantly governed by the internal friction within the aggregate-steel fiber system. And the increasing particle packing density reduced the macroscopic porosity of concrete and improved the uniformity of pore distribution, thereby enhancing its 3-day and 7-day compressive strength. On the other hand, the increased particle packing density decreased the uniformity of steel fiber distribution, which in turn adversely affected the 28-day compressive strength. Besides, a higher volume fraction of steel fibers oriented at 0–10° to the casting surface was observed in concrete with higher packing density, which significantly improved the 28-day flexural strength. The resistance of concrete to chloride ion penetration was not directly related to its packing characteristics. However, it was reduced by an increase in the total specific surface area of coarse aggregates and by a larger volume fraction of steel fibers oriented within 0–45° to the casting surface. Finally, comprehensive evaluation of aggregate packing characteristic dependent fresh and hardened properties of concrete lining segments were conducted to providing references for the design of high-quality segment concrete. • Concrete static flowability increases with aggregate-fiber system packing density. • Inter-particle friction significantly impacts concrete flow under vibration. • An increase in inter-particle packing density improves concrete porosity and early strength. • Increasing packing density elevates the volume fraction of fibers aligned with tension, enhancing flexural strength. • The total aggregate surface area and fiber orientation jointly govern concrete’s chloride resistance.