FIBRE REINFORCED CONCRETE WALLS AND SLABS: IN SITU PROPERTIES DETERMINED ON BEAMS

Most of the generally accepted test methods for determining the residual tensile strength, the main FRC design parameter, are based on bending of laboratory beams. Considering differences between the laboratory test methods and real structures, major uncertainties are due to anisotropic fibre orientation and the actual fibre content. One method proposed in the Norwegian guidelines for design, execution and control of steel fibre reinforced concrete, is applied in several field test programs the last years. It is based on beams 150xhx600 mm sawn out from structures (of thickness h) exposed to four-point bending. Furthermore, fibre counting in critical sections to determine the so-called orientation factors, which again can be used to determine a direction-dependent residual tensile strength, have been conducted. Utilizing this method, both favourable and unfavourable fibre orientation can be accounted for. A method for fibre counting on drilled cylinders is also used and evaluated. Results from three field test series are referred in this paper, and the investigated parameters are: (1) horizontally vs vertically cast elements, (2) horizontal vs vertical beams in wall elements, (3) Vibrated vs self compacting concrete, and (3) influence of casting point location in walls