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Article
Effect of Re-vibration Process on Axial Capacity of Short Reinforced Concrete Circular Columns

Author: S.A. Abbas
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2017 Volume: 35 Issue: 7 Part (A) Engineering Pages: 776-787
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

A considerable amount of research work has been performed on the effects of vibrating of fresh concrete on the reduction of shrinkage and creep, the improvement bond stress between reinforcing bar and concrete, reduction the concrete permeability and improvement of the mechanical properties of concrete (tension and compression). Series of tests on reinforced concrete circular column, cubes and cylinders were carried out to study the effect of re-vibration duration on axial strength of column, compression strength of concrete cubes, and tensile strength of cylinders. Different compressive strengths of concrete and different size of aggregate were considered in this investigation. The test results show that, the re-vibration operation improves the tensile and compressive strength of concrete. The stiffness of columns increased with increasing the re-vibration duration up to1.5 times the initial vibration duration. Size of aggregate has significant effect on the improvement properties of concrete due to re-vibration. Increase the time duration of re-vibration delay the appearance of first crack.


Article
Effect of Waiting Time before Re-vibration on Mechanical Properties of Fiber Reinforced Concrete

Author: Aseel A. Abdulridha
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2018 Volume: 36 Issue: 7 Part (A) Engineering Pages: 748-758
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

A knowledge of the concrete vibration after casting have led to improve the mechanical properties of concrete, reduce the deformations due to creep and shrinkage and reduce the concrete permeability. At the Structural and Material Laboratories- Building and Construction Engineering Department, University of Technology, series experimental tests on prisms, cubes and cylinders were carried out to investigate the effect of waiting time after initial vibration on the flexural-tensile strength, compressive strength and splitting tensile strength of fiber reinforced concrete. The variables considered in this study were; the amount of steel fiber and waiting time after initial vibration. The test results showed that the concrete prisms without steel fiber show approximately linear behavior till the maximum flexural-tensile load due to brittle behavior of concrete. The maximum improvement in flexural-tensile strength of concrete prism occurs after the initial setting of concrete i.e after 90 minutes of waiting time. The re-vibration after time period increase the stiffness of concrete prism in case of presence of steel fiber compared with the prisms initially vibrated only. The modulus of rupture of concrete prism increased with the increasing of steel fiber content for all waiting time before re-vibration.

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