The use of recycled concrete aggregates (RCA) in high performance concrete (HPC) was analyzed. The paper presents the experimental studies of model reinforced concrete beams with a rectangular section using high-performance recycled aggregates. Two variable contents of recycled aggregate concrete were used in this study: 50% and 100%. The experimental analyses conducted as immediate studies concerned the following issues: short time loads-deflection, load-carrying capacity of beams, deformation of concrete, cracks, and long-term loads-deflection. The comparative analysis involves the behavior of beams made of high performance concrete-high strength concrete (HPC-HSC) recycled aggregates with model control elements made of regular concrete based on natural aggregates. The deflection values for the recycled aggregate beams were 20% higher than in the case of the control beams made of HPC-HSC exclusively. Replacement of aggregate with recycled concrete aggregate resulted in a large decrease in the value of these two parameters, i.e., compression strength by about 42% and modulus of elasticity by about 33%.

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.

The paper summarises the experimental and numerical analysis of flexural capacity and deformability of structural concrete beams prepared as composite members consisting of two concrete layers made of reinforced normal concrete and high-performance concrete (HPC). The reinforced concrete composite beams used in the tests were prepared in full scale with the cross-section of 120 x 200 mm and the effective span of 2950 mm. The basic samples were composed in two layers consisting of highperformance concrete as the top layer, and normal strength concrete. The results of the analyses confirm a significant improvement of structural properties of composite beams in comparison to the beams prepared totally of normal concrete, and in some cases also in comparison with the beam totally made of HPC.

The paper summarises the experimental and numerical analysis of flexural capacity and deformability of structural concrete beams prepared as composite members consisting of two concrete layers made of reinforced normal concrete and high‐performance concrete (HPC). The reinforced concrete composite beams used in the tests were prepared in full scale with the cross‐section of 120 × 200 mm and the effective span of 2950 mm. The basic samples were composed in two layers consisting of high‐performance concrete as the top layer, and normal strength concrete. The results of the analyses confirm a significant improvement of structural properties of composite beams in comparison to the beams prepared totally of normal concrete, and in some cases also in comparison with the beam totally made of HPC.

The application of recycled coarse aggregates (RCA) in high-performance concrete (HPC) was analyzed in the article. In the paper, the behavior of HPC with coarse recycled aggregate and natural coarse aggregate (NCA) was compared. Short-term experiments were conducted, including concrete deformation, deflection, load bearing capacity, and cracking of beams. The analysis involved reinforced concrete T-beams made in 100% of RCA or NCA. The studies indicated that the beams with recycled aggregate are characterized by greater deflection and 7.6% lower load bearing capacity in comparison to the beams with NCA. Substitution of coarse natural aggregate with RCA reduced the compressive and tensile strengths by 20 and 26 (%), whereas and the modulus of elasticity was decreased by 15%.