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Showing 1-5 of 26 Abstracts search results

Document: 

SP253

Date: 

July 31, 2008

Author(s):

Editors: E. P. Figueiredo, T. C. Holland, V. M. Malhotra, and P. Helene

Publication:

Symposium Papers

Volume:

253

Abstract:

This ACI Special Publication (ACI SP-253) CD-ROM contains 25 papers from the Fifth ACI/CANMET/IBRACON International Conference on High-Performance Concrete Structures and Materials that was held in Manaus, Amazon State (AM), Brazil, June 18-20, 2008. Topics include Durability, Self-Compactability, Curing, Retarders, and Abrasion Resistance. The Fifth Conference is a result of the collaboration of ACI and CANMET along with Sao Paulo University, Federal University of Goias, Amazon State University, and Brazilian Concrete Institute (IBRACON).

DOI:

10.14359/19933


Document: 

SP253-17

Date: 

July 31, 2008

Author(s):

F.S. Bertolucci, M.P. Barbosa, G. de Freitas Maciel, F.L. dos Santos, and F.M. Salles

Publication:

Symposium Papers

Volume:

253

Abstract:

Rheology has the purpose to study the flux and deformation of materials when submitted to some tension or outer mechanical solicitation. In practice, the effective scientifi c fi eld broached by rheology is restricted only to the study of homogeneous fluids behavior, in which are included eminent liquids, particles suspensions, and emulsions. The viscosity (?) and the yield stress (t0) are the two basic values that defi ne the fl uids’ behavior. The fi rst one is the proportionality constant that relates the shear rate (?) with the shear stress (t) applied, while the second indicates the minimal tension for the fl owage beginning. The fluids that obey the Newton’s relation - Newtonians fluids - display the constant viscosity and the null yield stress. It’s the case of diluted suspensions and grate amount of the pure liquids (water, acetone, alcohol, etc.) in which the viscosity is an intrinsic characteristic that depends on temperature and, in a less signifi cant way, pressure. The suspension, titled "Cement Paste," is defined as being a mixture of water and cement with, or without, a superplasticizer additive. The cement paste has a non-Newtonian fl uid behavior (pseudoplastic), showing a viscosity that varies in accord to the applied shear stress and signifi cant deformations are obtained from a delimited yield stress. In some cases, systems can also manifest the infl uence of chemical additives used to modify the interactions fluid/particles, besides the introduced modifi cations by the presence of incorporated air. To the cement paste the rheometric rehearsals were made using the rheometer R/S Brookfi eld that controls shear stress and shear rate in accord to the rheological model of Herschel-Bulkley that seems to better adapt to this kind of suspension’s behavior. This paper shows the results of rheometrical rehearsals on the cement paste that were produced with cements HOLCIM MC-20 RS and CPV- ARI RS with the addition of superplasticizer additives based of napthaline and polycarboxilate, with and without a constant agitation of the mixture. The obtainment of dosages of superplasticizer additives, as well as the water/cement ratio, at the cement at the fl uidity rate determination, was done in a total of 12 different mixtures. It’s observed that the rheological parameters seem to vary according to the cement type, the superplasticizer type, and the methodology applied at the fl uidity rate determination.

DOI:

10.14359/20179


Document: 

SP253-13

Date: 

July 31, 2008

Author(s):

M.J. Positieri and P. Helene

Publication:

Symposium Papers

Volume:

253

Abstract:

Structural colored concrete is a material which offers differentiated beauty patterns, breaks the monotony of structures, and can be more economical as a surface finish choice. Studies related to this kind of special concrete are innovative because there is both a lack of research and sparse bibliography on this subject, particularly in connection with durability. The influence of pigments on concrete properties and durability is still a question of discussion and research. In fresh concrete, the pigment characteristics can affect mixture workability. In hardened concrete, pigments can affect compressive strength, and there is not enough information in relation to color stability and durability. This research covers colored concretes with red, black, and yellow pigments (iron oxides) compared with standard concrete. Their performance related to color stability and surface changes, physicomechanical properties and some traditional durability parameters. The conclusion shows that this kind of concrete can perform well if some care is taken.

DOI:

10.14359/20175


Document: 

SP253-25

Date: 

July 31, 2008

Author(s):

J.F. Fernandes, T.N. Bittencourt, and P. Helene

Publication:

Symposium Papers

Volume:

253

Abstract:

This paper presents a review of the application of concrete to offshore structures in the last 35 years. The state-of-the-art technology available for offshore oil platforms and other offshore applications is also described. Currently, there are around 350 offshore gravity and floating concrete platforms in operation in the North Sea, Northern Canada, Australia, Netherlands, Congo, Nigeria, Indonesia, Russia, the Philippines, Brazil, and the Gulf of Mexico. More recently, an important LNG offshore terminal has been designed and is now under construction in Algeciras, near the Gibraltar Strait in Spain. Over the past 30 years there has been a considerable improvement in the design and construction aspects of concrete production. Water-reducing admixtures and additions, such as metakaolin and silica, allowed the development of concretes with improved performance. These new concretes can easily achieve much higher strengths and durability which make them much more suitable for offshore applications. The liberal use of lightweight aggregates is considered crucial for a total weight reduction of the structure and for floating considerations. The evolving technology for the design and construction of this type of structures is discussed.

DOI:

10.14359/20187


Document: 

SP253-19

Date: 

July 31, 2008

Author(s):

E. Moreno, R. Solís-Carcaño, and C. Serrano-Zebadua

Publication:

Symposium Papers

Volume:

253

Abstract:

The weather of the Yucatan Peninsula is classifi ed as hot sub-humid, with minor differences of relative humidity and temperature during the year. Local builders, in their search for process optimization and cost reduction, usually do not cure concrete beyond wetting the concrete surface immediately after removing the formwork. Teaching of concrete technology has been based on classic reports, where it is affi rmed that the strength gain is enhanced when moist curing is applied. Preliminary studies in the Yucatan region have not shown that moist curing helped to improve strength gain. Based on the meteorological conditions of the Yucatan region, it is possible that natural curing occurred with no need for additional curing for most of the cases. The objective of this study was to obtain the strength-gain curves as a function of the moist curing time from 0 to 90 days. Preliminary results confirm the hypothesis about the suffi ciency of the natural curing under the weather conditions of the Yucatan region. The use of porous aggregate may have contributed to curing during storage in air.

DOI:

10.14359/20181


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