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International Concrete Abstracts Portal

Showing 1-5 of 14 Abstracts search results

Document: 

SP249

Date: 

March 1, 2008

Author(s):

Editors: R.Detwiler, K.Folliard, J.Olek, J.S. Popovics, and L.Snell / Sponsored by: ACI Publications Committee and ACI Committee 120

Publication:

Symposium Papers

Volume:

249

Abstract:

SP-249 This publication is a collection of 13 papers that have significantly influenced the field of concrete and cement-based materials over the years. The subject matter of the selected landmark papers represents a broad range of topics, from the analysis of the chemical composition of portland cement to the development of fracture models of concrete in computational simulations. The objective of this publication was to increase awareness of the significance of concrete materials research as a whole and therefore raise the profile of the field. In this volume, each landmark paper is preceded by a foreword written by an expert on the specific topic of the paper. Editorial in nature, these forewords serve to guide the reader through the content of the paper, to illuminate the significance of its contribution to the technical community, and in some cases, to reveal interesting historical context on the landmark work and its authors.

DOI:

10.14359/19748


Document: 

SP249-10

Date: 

March 1, 2008

Author(s):

A.S. Ngab, F.O. Slate, and A.H. Nilson

Publication:

Symposium Papers

Volume:

249

Abstract:

The realtionship between tiem-dependent deformation and internal microcracking of high strength concrete was investigated experimentally. Direct comparison was made to the behavior of normal strength concrete subjected to similar relative uniaxial compressive stresses and under the same environment conditions. Sealed and unsealed specimens were analyed for microcracking after they were subjected to short-term loading, to shrinkage, and to sustained loading. Results confirm that microcracking, always present eve in unloaded specimens, is increased by short-term loading, shrinkage, and sustained loading. However, the amoutn of cracking, as well as the increase relative to the initial state, is significantly less in high strength concrete than in normal strength material. The amount of creep strain associated with internal cracking in high strength concrete is negligible, whereas such creep is significat in normal strength concrete, particularly at high stresses. The research also indicates that the ratio of the sustained load strength to the short-term strength is higher for high strength than for normal strength concrete. This also can be explained in terms of differences in microcracking. Time-dependent engineering properties for high strength concrete, such as creep coefficient, specific creep, and shrinkage characteristics, are reported in a separate paper.

DOI:

10.14359/20131


Document: 

SP249-11

Date: 

March 1, 2008

Author(s):

A. Hillerborg, M. Modeer, and P.E. Petersson

Publication:

Symposium Papers

Volume:

249

Abstract:

Due to copyright issues, this paper is only available by purchasing the SP-249.

A method is presented in which fracture mechanics is introduced into finite element analysis by means of a model where stresses are assumed to act across a crack as long as it is narrowly opened. This assumption may be regarded as a way of expressing the energy absorption Gc in the energy balance approach, but it is also in agreement with results of tension tests. As a demonstration the method has been applied to the bending of an unreinforced beam, which has led to an explanation of the difference between bending strength and tensile strength, and of the variation in bending strength with beam depth.

DOI:

10.14359/20132


Document: 

SP249-08

Date: 

March 1, 2008

Author(s):

C.A. Menzel

Publication:

Symposium Papers

Volume:

249

Abstract:

Due to copyright issues, this paper is only available by purchasing the SP-249.

Cracks often develop in the surface of fresh concrete soon after it has been placed or finished and while it is still in the plastic state. The development of such cracks, commonly referred to as plastic cracking, can be practically eliminated if appropriate measures to minimize the causes are taken at the right time. The development, location and extent of cracks in fresh concrete may be readily observed if they occur in the exposed top surface. However, cracks may also develop, though much less frequently, in the vertical surface of fresh concrete slabs in horizontal forms. Cracks in vertical surfaces are seldom due to drying shrinkage, which is the most frequent cause of top-surface cracks.

DOI:

10.14359/20129


Document: 

SP249-07

Date: 

March 1, 2008

Author(s):

T.C. Powers and R.A. Helmuth

Publication:

Symposium Papers

Volume:

249

Abstract:

Due to copyright issues, this paper is only available by purchasing the SP-249.

New experimental data are presented on the freezing of hardened portland-cement pastes with and without entrained air. They are explained in terms of two mechanisims: 1) the generation of hydraulic pressure as water freezes in capillary cavities and 2) the growth of the bodies of ice in the capillary cavities or air voids by diffusion of water from the gel. Air voids limit the hydraulic pressure and shorten the period during which the ice in the cavities can increase. The closer the air voids are to each other the more effective they are in controlling either mechanism.

DOI:

10.14359/20128


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