Structural behaviour of layered beams with fibre-reinforced LWAC and normal density concrete

Abstract

The hybrid concrete structures investigated in this project were beams composed of two layers of different types of concrete. Normal density concrete (NC) was used in the top layer combined with a layer of fibre-reinforced lightweight concrete (FRLWC). Hence, the beams had a low weight and the NC layer fulfilled the requirements for ductility in compression. The material properties of the FRLWC were investigated through small-scale tests, the uniaxial tension test, the 3-point bending test and a compressive test on concrete cylinders/cubes. The small-scale tests constituted the basis for obtaining design parameters used in the design of the larger hybrid beams. These beams had 0.5 and 1.0 % of steel fibres, and were subjected to a 4-point bending test in order to study the performance in terms of both shear and bending actions. Fibre counting was carried out in order to relate the performance to the number of fibres crossing the critical section, which turned out to have a considerable influence on the performance of the FRLWC. In general, the types of failure were as expected. This study shows that the concept of combining NC and FRLWC in one cross-section shows promising results, and no problem with the bond between the layers of concrete was registered. Steel fibre reinforcement of the lightweight concrete increased the ductility in tension, so the amount of conventional shear reinforcement could be reduced. The concept provides a low self-weight of the structure, practical solutions in the construction phase and good premises for more efficient building.