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Showing 1-5 of 46 Abstracts search results

Document: 

SP186-45

Date: 

May 1, 1999

Author(s):

R. N. Swamy

Publication:

Symposium Papers

Volume:

186

Abstract:

Corrosion of steel reinforcement is now universally recognized as the major factor affecting the material stability and structural integrity of concrete structures. In very aggressive environments, the material degradation and structural distress arising from steel corrosion can reduce dramatically and useful service life of structures, affect their strength, stability and safety, and indeed, even lead to premature failure. The aim of this paper is to offer an integrated, holistic approach-a global design/management strategy-which will enable us to design new structures with a specified durable service life, and which will also enable us to enhance the durable service life of existing deteriorating structures. The paper identifies the design parameters that need to be satisfied and the strategy that needs to be adopted to ensure long-term corrosion-free service life of concrete structures, whether they are to be newly built or are existing but deteriorating due to environmental attack or otherwise damaged. The paper is accompanied by relevant and appropriate test data.

DOI:

10.14359/5590


Document: 

SP186-39

Date: 

May 1, 1999

Author(s):

S. Rols, M. Mbessa, J. Ambroise, and J. Pera

Publication:

Symposium Papers

Volume:

186

Abstract:

Very-high strength concrete (>100 MPa) has been developed using different types of ultra-fine particles: silica fume, ground granulated blast furnace slag, metakaolin, and cristobalite. The effect of the type of ultra-fine particle on some engineering properties of concrete has been investigated: compressive strength, loss of workability and plastic shrinkage. The highest level of strength (120 MPa) was obtained using either 20% slag, or 10% metakaolin, in addition to cement. The workability was maintained for one hour when slag or cristobalite were presenting the mixture. The tests undertaken on plastic shrinkage pointed out that very-high strength concrete developed high plastic shrinkage, specially when pozzolans were used. The use of slag does not affect the plastic shrinkage.

DOI:

10.14359/5584


Document: 

SP186-17

Date: 

May 1, 1999

Author(s):

R. Torrent

Publication:

Symposium Papers

Volume:

186

Abstract:

The objective of this paper is to report test results of gas-permeability of high-performance concretes, measured on laboratory specimens and directly on site. The test refer to three concretes used in two projects: a tunnel (50MPa concrete) and a cable-stayed bridge deck (50 Mpa concrete) and pylon (75 MPa concrete). In particular, the investigation was focused on comparing the permeability of the "covercrete", measured on laboratory specimens, with that measured directly on the site concretes, I.e. subjected to strongly different placing, compaction and curing conditions. The air-permeability of the cover of the three concretes was measured with a non-destructive technique, which takes into account the effect of moisture. Cores were drilled from the same elements and the oxygen permeability measured on them. When core-drilling was not allowed, parallel tests were conducted on large cubes, site cured, cast with the same concrete mixture used for the actual construction. For the three structures investigated, the air-permeability of the site concrete was higher that that measured on the companion laboratory specimens. The largest difference was found for the 75 Mpa-strength concrete; this difference is attributed to thermal cracking in the pylon, the center of which exhibited 55 degrees C temperature rise. This indicates the risk of impairing the potential durability of HPC through inappropriate practices. The results presented show the importance of checking the quality of the concrete, not only on laboratory-prepared specimens, but also directly on site.

DOI:

10.14359/5562


Document: 

SP186-19

Date: 

May 1, 1999

Author(s):

M. Stroeven and P. Stroeven

Publication:

Symposium Papers

Volume:

186

Abstract:

A "realistic" structural computer simulation system, SPACE, has been developed to assess the characteristics of dense random packings of particles in opaque materials like concrete. The paper presents a short introduction to the system, thereby only dealing with the essential design features. Nest, some applications to particle packing problems will be demonstrated, in which use is made of the simulation system. It will be shown that it can be a useful tool to support or even to evaluate experimental studies. But most of all, it will be shown that it can offer information on structural details that can not be obtained in another way, or only at the expense of considerably more effort. These structural details provide insight into complicated assessed that interface discontinuities in a particulate composite will extend much further into the interior of the material body than suggested by density or porosity measurements near such interfaces.

DOI:

10.14359/5564


Document: 

SP186-02

Date: 

May 1, 1999

Author(s):

J. G. Cabrera and C. D. Atis

Publication:

Symposium Papers

Volume:

186

Abstract:

This paper discusses a new method for the determination of the optimum W/C plus FA for maximum compaction of no slump concrete made with high volumes of fly ash. It explores the effect of fly ash fineness and particularly, carbon content on the explores the effect of fly ash fineness an particularly, carbon content on the compressive strength of the mixtures made with 50% and 70% replacement of normal portland cement with fly ash. By using an appropriate surfactant the no slump concrete mixtures are rendered workable and suitable for structural applications. The strength attained at 28 days is 60 Mpa or more, and therefore these mixtures are considered to yield high-strength concrete. The performance of the high-volume fly ash concrete is assessed in terms of abrasion and fatigue resistance that are the most appropriate performance indicators for concrete that will be used for the construction of pavements.

DOI:

10.14359/5547


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