Strength and Deformability Estimation of Centrifuged Concrete/Оценка прочносто и деформативности центрифугированного бетона

Influence of several factors, namely high strength longitudinal reinforcement, transverse (spiral) reinforcement, precompression level and concrete age, on mechanical properties of centrifuged concrete is investigated. It has been established by tests that longitudinal and transverse (spiral) reinforcement make worse compaction, casting and hardening conditions of centrifuged concrete. But the spiral reinforcement reduces transverse deformations of compressed centrifuged members of ring cross-section and hence increases concrete strength. During the experiments for central compression, centrifuged concrete members of a ring cross-section were investigated. The parameters of these members: diameter 260 and 500 mm, height 400 and 800 mm, web thickness 35…80 mm. The specimens were reinforced by longitudinal bars of 10, 12, 14 mm diameter and 4 or 5 mm cross-section spirals. Coefficient of longitudinal reinforcement μ s, varied from 1,5 to 6%, coefficient of transverse reinforcement μ cir —from 0,25 to 1,25%, lead of spirals—from 40 to 100 mm. During testing the ring concrete compressive strength Rb was 30…60 MPa. The results of the above-mentioned experiments are presented in Tables 1, 2 and 3. It is recommended to evaluate the reinforcement influence on mechanical properties of such concrete in members of real constructions by formulas (5) and (6). Relationships of concrete strength, initial modulus of deformation and intensity of precompression (9) and (10) are discussed in this article. The latest test results on relationship between concrete compression, tension strength and concrete age are presented. It is established, that hydration of cement takes quite a long time and compression and tension strength of centrifuged concrete increases. This increase in strength is given in Table 4. The strength of centrifuged concrete of 14, 120, 240 and 360 days was determined by direct compression and tension of concrete rings (Table 4). After 9,600 days (26 years) due to a limited number of specimens (concrete rings) the compressive strength was determined by testing prisms cut from the rings. The tensile strength was determined indirectly—by cutting these prisms, as it is recommended by a standard [11] according to formula (12). The results of these tests are presented in Tables 5 and 6. Theoretical connection between tensile and compressive strength may be described by Ferret formula (13), which we propose to use in a slightly changed form, i. e. as (14). Comparative calculations showed that the centrifuged concrete strength calculated according formula (14) corresponds to the results of direct testing (Table 7).

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