The thesis is a theoretical and experimental study of high-strength fiber-reinforced concrete with composite dispersed reinforcement with improved characteristics. On the basis of the analysis of a complex of experimental-statistical models of strength parameters of steel-fiber reinforced concrete, the efficiency of application for heavy and fine-grained concrete wavy steel fibers with increased surface of adhesion to concrete has been established. Quantitative dependencies were obtained that characterize the influence of the water-cement ratio and the fiber content on the strength of steel-fiber
reinforced concrete at compressive and flexural tensile strength as well as their correlation. It is shown that application of fine-grained concrete on the studied types of fibers can increase the efficiency of the disperse reinforcement (ie, the ratio of flexural tensile strength to compressive strength) by more than twice as compared to unreinforced concrete and by 20...25% compared to coarse-grained.
The optimum content of steel fibers is determined by means of experimental statistical models in the conditions of providing maximum values of flexural tensile strength and, accordingly, of the efficiency of disperse reinforcement. With optimal values of the fiber content for different types of fiber-reinforced concrete, the coefficient of dispersion reinforcement efficiency increases by 25 ... 40%.
The effectiveness of the use of a basalt fiber in the length of fibers 12 mm in a complex with wavy steel fiber, in optimal proportions is established. Quantitative dependences were obtained characterizing the influence of water-cement ratio, cement consumption, the content of steel and basalt fibers on the compressive and flexural tensile strength of composite fiber-reinforced concrete, as well as their ratio.
The influence of the mobility of the concrete mixtures and the duration of its vibration compaction on the coefficient of bundle (homogeneity) is studied. It has been established that for fiber concrete with composite dispersed reinforcement with the same duration of vibration sealing, the bundle is smaller than for steel fiber concrete. Experimentally confirmed the hypothesis about the possibility of avoiding or significantly reducing the fiber concrete mixtures and enhancing the uniformity of the structure of fiber concretes due to composite dispersed reinforcement. The complex of properties of fiber concretes, which characterize the features of their structure, deformability and frost resistance is studied. The best characteristics of porosity are fiber concretes with composite dispersed reinforcement.
It has been experimentally determined that for fiber concretes, especially composite, with increasing the duration of hardening up to 28 days, the ratio of flexural tensile strength to compressive strength (fc,tf / fcm), which does not directly characterize the elastic properties of concrete, decreases significantly to a lesser extent than for concrete without dispersed reinforcement. A significant increase in the ratio of flexural tensile strength to compressive strength in the case of use in a fiber concrete of a basalt fiber. Comparing analogous steel fiber concretes and composite fiber concretes, the growth of this ratio for composite fiber concretes is noted at 10...25%. Disperse reinforcement of concrete can be considered as an additional factor, along with reduced capillary porosity, which further affects the frost resistance. Experimental studies have shown that for polydispersed reinforced fiber concretes at a flow of fibers of 100 kg/m3, a frost resistance of up to 500 cycles is achieved, and with superplasticizers added – 600...800. It was established that polycarboxylate superplasticizer allows to receive fiber reinforced concrete with a frost resistance of 800 and more cycles. The increase of impact strength of fiber concrete in 6...7 times in relation to control non-reinforced concrete depending on the type and content of reinforcing elements is
established. The maximum absorption of impact energy is provided by steel fibers in a сomposition with basalt fibers. In the work, the design methods are proposed and the composition of fiber concrete with composite dispersed reinforcement is developed, which includes steel and basalt
fibers with high early strength. Also, the technical and economic advantages of polydispersed reinforced concrete in comparison with steel fiber reinforced concrete have been experimentally confirmed.
