Steel Fiber-Reinforced Concrete for Precast Tunnel Lining Segments

Precast tunnel lining segments are often subjected to critical impact and concentrated loads especially during the construction stage. The peripheral regions of segments, such as edges and corners, are usually exposed to significantly higher stresses than the interior. Under such high stress concentrations, concrete damages in the form of cracking and spalling are very likely to occur in these surface-near areas. Compared to conventional rebar reinforcement, owing to the crack-bridging effect and a randomly discrete distribution in the matrix, steel fibers can also be used to strengthen the concrete structure, even in the concrete cover.

Based on this fact, a new design concept to manufacture hybrid segments can be feasible. In this paper, hybrid concrete specimens consisting of steel fiber-reinforced concrete in the surface-near layer and plain concrete in the interior were produced by means of a special concreting technique. To simulate the segments subjected to local forces on a small-scale, a concentrated load was transmitted onto the upper surface of these specimens through a steel block. Parameters governing the load-bearing and fracture behaviour of concrete under concentrated load, such as load eccentricity, thickness of fiber reinforcement, casting direction and fiber-cocktail, were investigated. The effects of these variables on the ultimate bearing strength, stress-displacement response, failure mode and crack pattern were analysed and discussed.