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CONTENTS
Volume 4, Number 1, February 2007
 

Abstract
Over the past decades, an enormous amount of effort has been expended in laboratory and field studies on concrete durability estimation. The results of this research are still either widely scattered in the journal literature or mentioned briefly in the standard textbooks. Moreover, the theoretical approaches of deterioration mechanisms with a predictive character are limited to some complicated mathematical models not widespread in practice. A significant step forward could be the development of appropriate software for computer-based estimation of concrete service life, including reliable mathematical models and adequate experimental data. In the present work, the basis for the development of a computer estimation of the concrete service life is presented. After the definition of concrete mix design and structure characteristics, as well as the consideration regarding the environmental conditions where the structure will be found, the concrete service life can be reliably predicted using fundamental mathematical models that simulate the deterioration mechanisms. The prediction is focused on the basic deterioration phenomena of reinforced concrete, such as carbonation and chloride penetration, that initiate the reinforcing bars corrosion. Aspects on concrete strength and the production cost are also considered. Field observations and data collection from existing structures are compared with predictions of service life using the above model. A first attempt to develop a database of service lives of different types of reinforced concrete structure exposed to varying environments is finally included.

Key Words
computer; concrete; corrosion; durability; modelling; service life; software; validation.

Address
V. G. Papadakis; Department of Environmental and Natural Resources Management, University of Ioannina,
GR-30100, Agrinio, Greece
M. P. Efstathiou; Patras Science Park S.A., Patras, Greece
C. A. Apostolopoulos; Department of Mechanical and Aeronautical Engineering, University of Patras, Patras, Greece

Abstract
This paper is concentrated on the behaviors of five different types of fiber reinforced concrete (FRC) in uniaxial tension and flexural impact. The complete stress-strain responses in tension were acquired through a systematic experimental program. It was found that the tensile peak strains of concrete with micro polyethylene (PEF) fiber are about 18-31% higher than that of matrix concrete, those for composite with macro polypropylene fiber is 40-83% higher than that of steel fiber reinforced concrete (SFRC). The fracture energy of composites with micro-fiber is 23-67% higher than that of matrix concrete; this for macro polypropylene fiber and steel fiber FRCs are about 150-210% and 270-320% larger than that of plain concrete respectively. Micro-fiber is more effective than macro-fiber for initial crack impact resistance; however, the failure impact resistance of macro-fiber is significantly larger than that of micro-fiber, especially macro-polypropylene-fiber.

Key Words
polypropylene fiber; polyethylene fiber; steel fiber; concrete; uniaxial tension; crack; complete stress-deformation curve; flexural impact behavior.

Address
School of Civil and Architecture Engineering, Beijing University of Technology, Beijing 100022, P.R. China

Abstract
Slipforming is a construction method in which the forms move continuously during concrete placement. This paper presents a numerical procedure based on the finite element method to simulate the thermal behavior of concrete during slipforming operations. The validity of the model was successfully tested by simulating a very complex but well documented field case of actual slipforming operations performed during the construction of an offshore concrete oil platform structure. The results obtained have been related to the shape of the concrete ?hardened front? in the forms, which allows quick evaluation of the operation. The results of the numerical investigation have shown that the shape of the hardened front? can be affected by the temperature of the fresh concrete and ambient conditions. For a given initial concrete temperature, there are limitations for the ambient temperature that, when exceeded, can create an unfavorable shape of the concrete ?hardened front? in the forms. Similarly, for a given ambient temperature,the initial concrete temperature should not be fall below an established limit in order to avoid unfavorable shape of the ?hardened front?.

Key Words
setting time; concrete; slipforming; mock-up times; hardened front; finite element analysis.

Address
Department of Civil Engineering, Ryerson University
350 Victoria Street, Toronto, ON M5B 2K3 Canada

Abstract
The objective of this paper is to provide experimental data on the propagation of curved crack-surfaces and the respective load-displacement diagrams for the validation of numerical models for cracking of concrete, subjected to three-dimensional stress states. To this end beam-shaped specimens are subjected to combined bending and torsional loading, leading to the formation of a spatially curved crack-surface. The experimental data contain the evolution of the load and of the strains at selected points in terms of the crack mouth opening displacement and the propagation of the crack surface.

Key Words
finite element method; concrete cracking.

Address
University of Innsbruck, Faculty of Civil Engineering, Technikerstrasse 13, A-6020 Innsbruck, Austria

Abstract
The discrete crack-concept is applied to study the 3D propagation of tensile-dominated failure in plain concrete. To this end the Partition of Unity Finite Element Method (PUFEM) is utilized and the strong discontinuity approach is followed. A consistent linearized implementation of the PUFEM is combined with a predictor-corrector algorithm to track the crack path, which leads to a robust numerical description of concrete cracking. The proposed concept is applied to study concrete failure during the PCT3D test and the predicted numerical results are compared to experimental data. The proposed numerical concept provides a clear interface for constitutive models and allows an investigation of their impact on concrete cracking under 3D conditions, which is of significant scientific interests to interpret results from 3D experiments.

Key Words
concrete cracking; partition of unity finite element method; strong discontinuity; 3D crack-tracking; PCT3D test.

Address
Royal Institute of Technology (KTH), Department of Solid Mechanics, Osquars backe 1, SE-100 44 Stockholm, Sweden


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