The paper presented aimed at examining the effect of a fiber-reinforced concrete layer in the compressed zone on the mechanical properties of composite fiber-reinforced concrete slabs. Steel fibers (SF) and polypropylene fibers (PP) in the amount of 1% in relation to the weight of the concrete mix were used as reinforcement fibers. The mixture compositions were developed for the reference concrete, steel fiber concrete and polypropylene fiber concrete. The mechanical properties of the concrete obtained from the designed mixes such as compressive strength, bending strength, modulus of elasticity and frost resistance were tested. The main research elements, i.e., slabs with a reinforced compression zone in the form of a 30 mm layer of concrete with PP or SF were made and tested. The results obtained were compared with a plate made without a strengthening layer. The bending resistance, load capacity and deflection tests were performed on the slabs. A scheme of crack development during the test and a numerical model for the slab element were also devised. The study showed that the composite slabs with fiber-reinforced concrete with PP in the upper layer achieved 12% higher load capacity, with respect to the reference slabs.
Keywords: bearing capacity; bending; cracks; deflection; frost resistance; polypropylene fibers; pores; reinforced concrete slabs; steel fibers.