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International Concrete Abstracts Portal

Showing 1-5 of 26 Abstracts search results

Document: 

SP253-21

Date: 

July 31, 2008

Author(s):

M. Nepomuceno and L. Oliveira

Publication:

Symposium Papers

Volume:

253

Abstract:

This paper reports an experimental study on the mortar phase for selfcompacting concrete. A series of mortars were produced with similar fl ow properties, measured by spread and v-funnel tests, adequate to produce self-compacting concrete. The water content and the modifi ed carboxylic superplasticizer dosage were determined experimentally for each mortar. Different percentages of cement replacement materials were used in binary blends, each one combining one of the two types of cement with one of the three mineral additions selected: limestone powder, granite fi ller, and fl y ash. Each of the binary blends of powders was combined in fi ve different proportions in volume with the fi ne aggregate (Vp/Vs). Mortars were tested for compressive strength at 28 days and this value was related to the water/cement ratio, the percentage of replacement materials, and Vp/Vs parameter. The analysis revealed the possibility of establishing adequate mortar parameters to obtain simultaneously the self-compactability and the required compressive strength of self-compacting concrete.

DOI:

10.14359/20183


Document: 

SP253-16

Date: 

July 31, 2008

Author(s):

B.F. Tutikian, D.C. Dal Molin, and R.A. Cremonini

Publication:

Symposium Papers

Volume:

253

Abstract:

In 1988, self-compacting concrete (SCC) - a high-fl uidity concrete that maintains its stability - was developed in Japan. However, even nowadays, there is still a lack of knowledge about SCC, especially regarding the few practical mix design methods available. Without a standardized mixture proportioning method, researchers have to use the trial-and-error method, spending time and resources without being certain about the concrete quality. In this paper, a new mix design method for SCC is introduced that allows the production of concrete from local materials, in an attempt to reach the desired mechanical and durability properties at the lowest cost. This method is explained in detail elsewhere. To explain how to use such a method, a family of SCC was carried out, presented at the end of the paper. Moreover, this methodology has been applied successfully in Brazil, obtaining SCC with costs very close to those of normal vibrated concrete (NVC) for the same strengths or durability measures.

DOI:

10.14359/20178


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


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: 

SP253-24

Date: 

July 31, 2008

Author(s):

M. Córdova and P. Castro-Borges

Publication:

Symposium Papers

Volume:

253

Abstract:

The galvanic couple effect decreases a few weeks after performing local repairs. Nonetheless, there is no information on the effect the anodic/cathodic area (aA/aC) ratio has on the magnitude of the galvanic couple. The selective use of stainless steel represents an alternative to repair of concrete structures, but it remains understudied, particularly in the tropical marine environments of the Gulf of Mexico. In this paper, we analyze and discuss the infl uence of the anodic/cathodic area ratio on the galvanic behavior of local repairs conducted on small beams made of low-quality concrete and 304 stainless steel (SS) bars. Results from this experiment indicate that an aA/aC ratio of more than 5 causes a signifi cant decrease in the galvanic couple of the adjacent areas.

DOI:

10.14359/20186


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