Evaluation of rheological and mechanical properties of fiber reinforced set-accelerated shotcretes for tunnel lining

The present paper deals with the use of different fibers (steel–SF, glass–GF and polypropylene-PF) to reinforce concretes and shotcretes (manufactured with a sodium silicate based set-accelerating admixture) for tunnel linings in order to compare rheological and mechanical behaviour of set accelerated fiber reinforced mixtures with respect to plain concrete. The effect of fibres on rheological and mechanical properties was evaluated. Shotcrete rebound was closely related to the dosage of set-accelerating admixture other than type and dosage of fibers. Strength gain and mechanical properties were strongly influenced by both the casting method and the dosage of set-accelerating product. Spraying and set accelerator dosage determine a sharp decrease in compressive strength compared that of concrete placed and vibrated without sodium silicate. Furthermore, the test results indicated that punching shear strength of FR mixtures was lower than that of steel mesh reinforced shotcrete without fibers as a consequence of the poor quality of the cement matrix due to the set-accelerator addition. Use of set accelerating admixture reduced the fiber-matrix bond lowering the punching shear strength of FR mixtures.