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International Concrete Abstracts Portal

Showing 1-5 of 14 Abstracts search results

Document: 

SP249-13

Date: 

March 1, 2008

Author(s):

T.C. Powers and T.L. Brownyard

Publication:

Symposium Papers

Volume:

249

Abstract:

This paper deals mainly with data on water fixation in hardened portland cement paste, the properties of evaporable water, the desnisty of the solid substance, and the porosity of the paste as a whole. The studies of the evaporable water include water-vapor-adsorption characteristics and the thermodynamics of adsorption. The discusssions include the following topics: 1. Theoretical interpretation of adsorption data 2. The specific surface of hardened portland cement paste 3. Minimum porosity of hardened paste 4. Relative amounts of gel-water and capillary water 5. The thermodynamics of adsorption 6. The energy of binding of water in hardened paste 7. Swelling pressure 8. Mechanism of shrinking and swelling 9. Capillary-flow and moisture diffusion 10. Esimation of absolute volume of solid phase in hardened paste 11. Specific volumes of evaporable and non-evaporable water 12. Computation of volume of solid phase in hardened paste 13. Limit of hydration of portland cement 14. Relation of physical characteristics of paste to compressive strength 15. Permeability and absorptivity 16. Freezing of water in hardened portland cement paste

DOI:

10.14359/20134


Document: 

SP249-12

Date: 

March 1, 2008

Author(s):

J.P. Romualdi and G.B. Batson

Publication:

Symposium Papers

Volume:

249

Abstract:

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

The application of linear-elastic fracture mechanics reveals that the strength of concrete in tension is limited by internal holes and micro-cracks. Fracture arrest can be achieved by reducing the spacing of reinforcement to a suitable scale. Reinforcement diameter decreases in proportion to reduction in spacing in order to maintain steel percentage. Theoretical results indicate that the tensile cracking strength of concrete increases in proportion to the inverse square root of the reinforcement spacing. Tests on closely spaced wire reinforced beams support the theoretical calculations.

DOI:

10.14359/20133


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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