Right: Spray panel
of concrete to be used, thus reducing the volume of
material to be excavated or, alternatively, saving space within the cross-section, in order to facilitate the long- term management of the structure. Specific technical strengths and weakness of the
different fibres available on the market are often less well-known, and this can lead to confusion. Fibres for concrete exist in all colours, shapes, sizes and materials. High performance Dramix steel fibres are suitable
reinforcement material for concrete in that: the thermal expansion coefficient is equal to that of concrete; the Young’s Modulus is at least five times higher than that of concrete; and, the creep of regular carbon steel fibres can only occur above 370°C. This performance (high tensile strength > 1800 MPa, optimised anchorage, and high l/d ratio to guarantee the minimum network required) allows a hardening post crack behaviour at section level, allowing crack control at Service Limit State and structural ductility at Ultimate Limit State. Consequently, justifying the mechanical behaviour
of fibre reinforced sprayed concrete for permanent or long-term temporary structures is a major issue for the development of this technical possibility. Testing to determine the residual strengths for sprayed
fibre reinforced concrete can be difficult because specimens for the beam tests must be cut from sprayed
panels. With the increased use of steel fibre reinforced for sprayed concrete lining (SCL) a new standard was developed that allows the residual strength parameters to be determined by performing a three-point bending test on the standard EN type square panel. The advantages of this new three-point bending test
on a notched panel method (EN 14488-3 Method b) in steel fibre reinforced SCL (SFRSCL) applications include: ● The geometry and dimensions of the specimens, as well as the spray method adopted will ensure distribution of the fibres in the matrix, which is close as possible to that encountered in the real structure;
● The dimensions of the test specimen will be acceptable for handling (no excessive weights or dimensions);
● The test will be compatible with use in many normally equipped laboratories (no unnecessary sophistication);
● The geometry is the same as in the plate test for Energy Absorption;
● The plate can be sprayed on the job site – Eliminates the need to saw a beam out of a panel;
● The scatter will be lower than the current standardised beam tests because of the larger specimen;
Right: Dramix EyeD Inspector
36 | September 2025
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