Abstract
The article develops methods and methodology for experimental studies of centrifuged and vibro-centrifuged concrete products of annular cross-section. They assess the real variatropy of the structure and confirm the correctness of the accepted research. An original technique for experimental studies of the variatropy of the cross-sections of vibrated, centrifuged and vibro-centrifuged concretes is proposed to determine their integral (common) and differential (differing in layers) strength and strain characteristics and deformation diagrams. It has been proved that with vibro-centrifugation it becomes possible to obtain concretes with improved structure and higher characteristics compared with centrifugation and vibration techniques. Experimental studies of the differential characteristics of centrifuged and vibro-centrifuged concretes under compression and tension revealed that the outer layer of concrete had the best characteristics after centrifugation and vibro-centrifugation, and the inner layer had the worst ones. The three-layer model of the variatropic structure for centrifuged and vibro-centrifuged concrete has been experimentally confirmed. The concrete of the outer layers had the highest strength and modulus of elasticity and the least deformability; the concrete of the inner layers had the lowest strength and modulus of elasticity and the highest deformability; and the concrete of the middle layers had average characteristics. The deformation diagrams of centrifuged and vibro-centrifuged concretes were also differentiated by layers, confirming the variatropy of the structure of such concretes. The deformation diagrams for the outer concrete layer demonstrated the highest strength; the diagrams for the inner concrete layer showed the lowest strength; and the diagrams for the middle concrete layer corresponded to mean characteristics.
Highlights
During operation, concrete undergoes various influences, the result of which are strength changes over time
The purpose of this paper is to study the characteristics of reinforced concrete structures with annular cross-sections, in particular, integral and differential structural characteristics of vibrated, centrifuged and vibro-centrifuged concretes of variatropic cross-sections using ultrasonic research methods
The results of experimental studies of the averaged integral characteristics of test concrete samples are shown in Table 2 and Figures 10–18
Summary
Concrete undergoes various influences, the result of which are strength changes over time. This change can take place in three directions:. (i) The strength of concrete may increase under favorable temperature and humidity conditions due to the continuing hydration of cement;. (iii) There is an intense accumulation of microdestructions in the concrete structure under the influence of the environment; due to unfavorable temperature and humidity conditions, the cement hydration is either completely absent or proceeds extremely slowly, and as a result, a steady decrease in the strength of concrete occurs. The first case is observed in the underground part of structures, where there are appropriate conditions for the continuation of cement hydration and the growth of concrete strength. It should be emphasized that the control should be non-destructive, while it should allow for assessing the strength of concrete at any stage of the operation of structures and degradation of the concrete structure
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