Experimental studies of fiber concrete creep

The results of two-stage experimental studies of the strength and deformation characteristics of fibrous concrete reinforced with steel fiber. In the experiments we used steel fiber with bent ends, which practically does not form "hedgehogs", which allows to achieve an even distribution of the fiber by volume. At the first stage, the cube and prismatic strength, deformability at central compression, a number of special characteristics are determined: water absorption, frost resistance, abrasion; the optimal percentage of fiber reinforcement and the maximum size of the coarse aggregate fraction were selected. Fiber reinforcement led to an increase in the strength of concrete at compression by 1,35 times and an increase in the tensile strength at bending by 3,4 times. At the second stage, the creep of fibrous concrete and plain concrete of similar composition at different stress levels was researched. Creep curves are plotted. It is shown that the use of fiber reinforcement leads to a decrease in creep strain by 21 to 30 percent, depending on the stress level

Influence of long-term compressive stresses on strength of concrete and steel-fiber concrete prismatic element

The strength and deformation characteristics of concrete and steel-fiber concrete on prisms and cubes are determined. Short-term and long-term tests of the samples were carried out taking into account the recommendations of the regulatory documents for the testing of concrete. Loading of samples with a long load was carried out in force installations (stands) consisting of four metal rods to which rigid loading plates were fixed at certain levels with threaded connections. To cover the entire operational spectrum of the stress state of real reinforced concrete elements, levels of 0.3; 0.4; 0.5; 0.67 and 0.8 from the short-term destructive load were adopted as long-term loading levels. All samples, which were more than a year under the action of a long-acting load, increased their bearing capacity. Prisms from steel-fiber concrete, which were under the influence of a long-acting load during 370 days, increased the bearing capacity, depending on the level of load, by 30-50%. The higher load level, the higher the creep rupture strength. When the loading was repeated before the destruction, the deformations of steel-fiberconcrete prisms changed linearly

Comparative analysis of strength and deformation of reinforced concrete and steel fiber concrete slabs

The results of experimental studies of the steel fiber influence on the bearing capacity, deformability and crack resistance of reinforced concrete multi-hollow plates are given. We investigated a serial floor slab and a similar one, but with the addition of steel fiber. Both plates are factory-made. For testing, the testing apparatus was designed and manufactured that made it possible to study full-size floor slabs in laboratory conditions. The tests were carried out according to a single-span scheme with the replacing equivalent load. The loading was carried out by applying two concentrated strip vertical loads along the plate width. The load was applied in steps of (0.04 ÷ 0.05) from the breaking load. Each stage ended with exposure lasting up to 10 minutes with fixing all the necessary parameters. Deformations were measured using dial gauges. From the moment the first crack appeared in the stretched zone of concrete, the process of crack formation and opening was monitored. At each level, using the Brunell tube, the width of their opening and height were measured. The moment of cracking in both slabs began at the same relative strain. It has been established that the bearing capacity and crack resistance of a slab of combined reinforcement using steel fiber are respectively 50 and 44% higher than that of a similar reinforced concrete slab. The maximum deflection of the slab of combined reinforcement is 37.5% lower than that of conventional reinforced concrete. The destruction of both slabs occurred under loads, when the relative deformations in the compressed zone of concrete reached 0.80×10-3 and 1.10×10-3 for reinforced concrete and steel-fiber concrete slabs, respectively, the difference is 37.5%