Fiber Reinforced High-Strength Shotcrete with Condensed Silica Fume


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Title: Fiber Reinforced High-Strength Shotcrete with Condensed Silica Fume

Author(s): Theodor A. Burge

Publication: Special Publication

Volume: 91


Appears on pages(s): 1153-1170

Keywords: accelerating agents; deflection; fiber reinforced concretes; freeze-thaw durability; high-strength concretes; metal fibers; modulus of elasticity; permeability; shotcrete; silica.

Date: 2/1/1986

To-day's advanced techniques in tunnelling and gallery engineering call for high-quality shotcrete, i.e. a material which develops accelerated set and high early strength to suit the safety requirements in the heading phase, and also final strength requirements for the perliminary concrete lining (New Austrian Tunnelling Method, NATM). High early strength can be obtained with the addition of an accelerator to the shotcrete mixture. Many materials are known for accelerating the setting time of shotcrete including strongly alka-line reacting materials such as alkali metal hydroxides, alkali metal carbonates, alkali metal aluminates and alkaline earth chlorides. The adverse effects of these admixtures are also known. With the development of an efficient alkali-free shotcrete accelerator it has become possible to produce high early strength without undesirable effects on the final strength. Attempts to positively influence the fracture characteristics of cement mortars or concrete with fibres have a long history, while organic fibres were soon discardes, great efforts are still being undertaken with glass and steel fibres. Problems in the processing of steel-fibres reinforced shot-crete motivated us to introduce a new type of fibre. The addition of condensed silica fume increased the strengths and reduced sharply the permability. The resistance to freezing and thawing was also greatly improved. No long-term strength loss was obtained due to the use of a new alkali-free setting accelerator.