The issue of increasing the corrosion resistance of composite reinforcement, based on glass fiber and epoxy anhydride binder, is considered. The proposed samples of composite reinforcement were manufactured by needle extrusion technology. Glass fibers were evenly distributed in the channels and impregnated with a polymer binder based on epoxy resin. The amount of phenolic modifier in the polymer binder, according to the technological mode of obtaining composite reinforcement, was brought up to 5%. With a further increase in the content of the modifier, the degree of conversion of epoxy groups was no more than 70%, which sharply reduced the operational characteristics of the material. The overall ratio of polymer binder and glass reinforcement in the composite was ~ 60÷40. It was established that at low concentrations of the polymer modifier (up to 5 wt. parts), the processes of ordering and chemical grafting lead to compaction of the molecular grouping in the system, which in our case is characteristic of phenolic resins of the novolach and resol types. At the same time, under the conditions of the production technology, internal stresses in materials of this type increase sharply, which leads to the formation of surface defects (microcracks). At the tip of a crack or defect, sodium ions or other cations under the action of water undergo hydrolysis to form metal hydroxide, which, in turn, causes hydrolysis of siloxane bonds, thus weakening the mesh structure of silicon dioxide. The experimental activation energy was identified with the activation energy of sodium ion diffusion in the glass mass. But the plastic deformation of the glass in the region before the crack is very small, and instead of a uniform distribution of stress, the material cracks along the weakened centers The obtained data indicate that the action of the alkaline environment causes an increased loss of mass of the composite, both for the unmodified and for those modified with traditional phenolic resins. In turn, this ensures a high degree of penetration of alkalis into the volume of the material, access to reinforced fibers with their subsequent damage. To increase the corrosion resistance of composite reinforcement based on an epoxy anhydride binder, it is advisable to use a reactive sulfur-containing phenolic modifier. Its action is based on the ability to maintain the permissible monolithicity of fiberglass in the alkaline environment of concrete, the modulus of elasticity and necessary strength. Keywords: composite polymer reinforcement, fiberglass, alkaline environment, phenolic modifier.
The scientific work is devoted to the interaction process of concrete and composite reinforcement, which is characterized by “adhesion-slip” dependence. It is known, that composite reinforcement does not behave in the same way as traditional steel reinforcement, because in some cases their mechanical properties differ significantly. CFRP/FGRP/BFRP products have higher strength, but a lower modulus of elasticity, so direct replacement of steel with such reinforcement is not always possible according to many constructional requirements. Adhesion forces create a complex stress-strain condition in concrete interacting with reinforcement. This condition leads to the distribution of loads along the axis of reinforcement, and, as a result, the longitudinal forces on reinforcement become variable along the entire length of the rod. A detailed analysis of the existing approaches to the problem of adhesion level of concrete and composite reinforcement is performed in article. It was determined that the complex multiparameter state of the interaction of concrete and composite reinforcement is characterized by the corresponding curves of “adhesion-slip” dependence, which can be obtained by two experimental methods (beam test method and direct pull-out test method). A theoretical research of the adhesion level of concrete and composite reinforcement (beyond the limits of cracks formation) was carried out, connected with the analysis of the distribution of deformations of concrete and reinforcement along the span of the element. Current analysis is based on the determination of a number of differential equations with a step-by-step description of adhesion level problems. The results of research can be used in future during the design and calculation of concrete structures reinforced with different types of composite reinforcement (based on basalt, glass, carbon fibers etc.), however, it is necessary to conduct further experiments into the long-term operation (behavior) of composite reinforcement over time under the influence of various factors, to establish a number of rheological aspects. Keywords: adhesion, calculation, algorithm, composite reinforcement, concrete, slip.
Scientific work is devoted to research of stress-strain state of PD2-9,5 road slabs, reinforced with identical frames made of fiberglass reinforcement and metal reinforcement A500C of the 10th diameter. In order to verify the hypothesis regarding the possibility of equal-strength replacement of metal reinforcement with composite reinforcement of a smaller diameter, glass composite reinforcement of the 7th diameter was used to reinforce the slab. To determine the actual bearing capacity, due to the application of a uniformly distributed load, a calculation scheme with a "beam" slab, i.e., resting on two supports, was applied. During the experiment, it was determined that the appearance, formation, and opening of normal cracks in both tested slabs corresponds to the "classic" nature of crack formation in reinforced concrete elements operating in bending. After the destruction of the slab reinforced with fiberglass composite reinforcement, numerous structural cracks of a mesh nature were recorded, with different degrees of branching, mainly in the lateral central part and in the lower (stretched) zone. The total final deflection in the center of the slab reinforced with fiberglass composite reinforcement at the time of failure was 3,41 cm, which significantly exceeds the permissible value for the span length L < 3 m. At the same time, the total deflection in the center of the slab reinforced with metal reinforcement at the current maximum uniformly distributed load ( without complete destruction of the slab) is 1,06 cm, which meets the generally accepted construction requirements. It was established that the actual bearing capacity of the road slab reinforced with A500C metal reinforcement is higher by 2,3 times than the bearing capacity of a slab with similar fiberglass composite reinforcement. This fact does not give grounds for asserting the effective use of Ø7 mm fiberglass composite reinforcement as a conditionally “equal-strength” replacement of Ø10 mm class A500C metal reinforcement when reinforcing elements of a similar type. To ensure structural requirements, it is necessary to significantly increase the diameter of the applied composite reinforcement, or, as an option, use combined reinforcement with a simultaneous combination of metal and composite reinforcement. Keywords: strength, composite reinforcement, stress-strain state, road slab.
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