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Showing 1-5 of 12 Abstracts search results

Document: 

SP156-03

Date: 

September 1, 1995

Author(s):

L. R. Taerwe

Publication:

Symposium Papers

Volume:

156

Abstract:

The fracture process of high-strength concrete (HSC) submitted to uniaxial compression was analyzed by means of loading tests on cylinders under special closed loop control. Conclusions were drawn from axial and circumferential strain curves, cross sections of specimens impregnated with a fluorescent dye, and visual observations. The evolution of the internal crack extension was revealed and it was shown that under stable progressive fracture, predominantly aggregate bond failure and crack branching occur with the cracks passing around the coarse aggregates. the onset of damage is explained in terms of elementary force transfer concepts. The influence of maximum aggregate size and fiber addition are also discussed in this paper.

DOI:

10.14359/938


Document: 

SP156-02

Date: 

September 1, 1995

Author(s):

Z. P. Bazant and R. Desmorat

Publication:

Symposium Papers

Volume:

156

Abstract:

The size effect caused by post-peak softening in the relation of interface shear stress and slip displacement between a fiber or reinforcing bar and the surrounding matrix was analyzed. The problem was simplified as one- dimensional. It was shown that the post-peak softening leads to localization of slip. The larger the bar or fiber size, the stronger the localization. The size effect in geometrically similar pullout tests of different sizes was found to represent a transition from the case of no size effect for small sizes to the case of a size effect of the same type as in linear elastic fracture mechanics, in which the difference of the pullout stress in the fiber and the residual pullout stress corresponding to the residual interface shear stress is proportional to the inverse square root of bar or fiber size. An analytical expression for the transitional size effect was obtained and was found to approximately agree with the generalized form of the size effect law proposed earlier by Bazant. Measurements of the size effect can be used for identifying the interface properties.

DOI:

10.14359/1019


Document: 

SP156-06

Date: 

September 1, 1995

Author(s):

A. Vervuurt and j. G. M. Van Mier

Publication:

Symposium Papers

Volume:

156

Abstract:

Crack propagation in composite materials is a very complex process. Of utmost importance seems the behavior of the interfaces between the constituting phases. In reinforced concrete, interfaces not only appear in the concrete itself, but also between the concrete and the steel reinforcement. Fracture of the steel-concrete interface can be seen as a combination of adhesion, mechanical interlock, and frictional stress transfer. In this paper, steel-concrete interface fracture is modelled at the meso level. At this level, a simple linear elastic fracture law seems to suffice to explain global fracture mechanisms of composite materials. Interfaces between aggregate and matrix and between matrix and reinforcing bars are simulated using a lattice model. In the model, the material is discretized as a lattice of brittle breaking beam elements. Disorder of the material is implemented by assigning different strength and stiffness properties to the beam elements. Cracking is simulated by removing in each load step the element with the highest stress over strength ratio. The model is applied to uniaxial tensile fracture of plain concrete specimens and to bond of steel to concrete. Comparison from the simulations presented in this paper with experimental data shows that crack mechanisms are simulated quite accurately. However, the bond-displacement behavior is still too brittle. This point can be improved when more detail is included in the material structure that is incorporated in the analysis. The macroscopic bond-slip behavior of a reinforcing bar depends strongly on the micro-cracking near the interfacial zone between concrete and reinforcing bar. The analyses clearly show the influence of adhesion between steel and concrete on the simulated crack patterns.

DOI:

10.14359/941


Document: 

SP156-10

Date: 

September 1, 1995

Author(s):

M. Kawamura and S. Igarashi

Publication:

Symposium Papers

Volume:

156

Abstract:

Fracture of the interfacial zone between a fiber and the cementitious matrix plays a significant role in the mechanical behavior of fiber reinforced cementitious composites. For better understanding of debonding characteristics of a fiber in the composites, the behavior of the extension of cracks along the interface was examined under the fluorescence microscope. The correspondence between the features of fracture zones obtained by the microscopic study and the fracture toughness for the interfacial zone is discussed in this paper. Examinations under the microscope revealed that the debonding and the extension of interfacial cracks were not caused by a simple shear failure at the actual interface, but were accompanied by local failures over relatively wide regions surrounding the steel fibers. The incorporation of silica fume resulted in the reduction in areas containing local failures along the interface. Fewer local failures in the interfacial zone in the steel fiber-silica fume-bearing cement composite were reflected by the decrease in the fracture toughness for the interfacial zone.

DOI:

10.14359/945


Document: 

SP156-08

Date: 

September 1, 1995

Author(s):

S. H. Li, S. P. Shah, Z. Li, and T. Mura

Publication:

Symposium Papers

Volume:

156

Abstract:

A new method to predict the debonding behavior of fiber-matrix interface has been proposed by applying the principles of the micromechanics of inclusion and fracture mechanics. The validity of the mathematical model is further verified by uniaxial tension tests carried out on steel fiber reinforced cementitious composite specimens by employing a digitally controlled closed-loop MTS testing machine. It was demonstrated that the debonding occurs before the bend over point; the debonded lengths are largely influenced by the sequence of the occurrence of transverse matrix cracks and the loading stage. A stable growth of debonding was observed in the investigation. The measured debonded lengths were compared with the theoretical prediction of the proposed model. A reasonable agreement was observed.

DOI:

10.14359/943


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