Volumes
Vol 2 - Num. 1 - September/2006


 



PAPERS - ARTIGOS

Evaluation of Pozzolanic Activity and Inhibition of the Alkali-Aggregate Reaction in Highly Reactive Pozzolans
Evaluation of Pozzolanic Activity and Inhibition of the Alkali-Aggregate Reaction in Highly Reactive Pozzolans
Full Paper: Ver trabalho ( inglês )   
M. S. BARATA, N. P. HASPARYK, F. S.S. LIMA
Abstract

This paper presents the results of an experimental study developed at the Federal University of Pará and at Furnas
Centrais Elétricas S.A. The study aimed to investigate the reactivity of three highly reactive pozzolans: silica fume, rice
husk-ash and metakaolinite, by determining the incorporation content of each for remotion of all the calcium hydroxide
(CH) and for reduction the alkali-aggregate reaction. At the evaluation of the CH consumption, pastes with pozzolan and
lime were cast in different proportions and observing compressive strength values in mini test specimens, correlating
the former with the calcium hydroxide contents of those pastes. The expansive behavior originating from the alkali-aggregate
reaction was assessed in the presence of reactive Pyrex-type glass, by means of mortar bars in the presence of
the three studied pozzolans, employing the ASTM C-1260 accelerated method. In this test, the pozzolans were employed
with contents of 4%, 8%, 12% and 16%, in addition to the reference sample. The results obtained indicated that the
silica fume and the metakaolinite were the pozzolans with greater pozzolanic activity as well as the most effective in
the reduction of expansions caused by the Pyrex glass reactivity. For total elimination of CH the optimum substitution
contents were around 22%, while for the rice husk-ash 30% were required. In expansion reduction, contents of 8% of
pozzolans were considered effective by mortar-accelerated test.

Keywords: alkali-aggregate reaction, calcium hydroxide, expansion, metakaolinite, pozzolan, reactivity, rice husk-ash,
silica fume.

Copyright © 2006 IBRACON. All rights reserved.
Critical Analysis on HPC with Very High Contents of Mineral Additions (Part I)
Mix Proportion and Carbonation

Critical Analysis on HPC with Very High Contents of Mineral Additions (Part I)
Mix Proportion and Carbonation

 Full Paper: Ver trabalho ( inglês )   
G. C. ISAIA, A. L. G. GASTALDINI

Abstract

The increasing number of researches and concrete structures made with HPC containing high contents of cement substitution
(above 50%, by mass) by mineral additions, has revealed apprehension among some researches on topics related
to durability of these concretes, especially carbonation, due to parameters used in the mix proportions. According them,
the low cement content combined with the great amount of mineral additions would induce increase in total water content
that, in spite of the lower water/cementitious materials ratio, would carry higher carbonation, possible leaching and
durability loss. This paper presents critical analysis concerning to these subjects, showing data of researches performed
by the authors, compared with others published by the literature. It is demonstrated that lower cement content, higher
total water per m³ of concrete, although entailing consequences to carbonation, preventive actions may overcome these
inconveniences in order to limit possible side effects, inducing the attainment of durable concretes, in such mix proportion
conditions. The addition of hydrated lime to the concrete mixtures in order to replace the alkaline reserve and the
possibility of the cement paste lixiviation is also discussed.

Keywords: mix proportion, carbonation, mineral additions, high contents, calcium hydroxide

Copyright © 2006 IBRACON. All rights reserved.
Influence of Testing Procedure on the Shrinkage of a High-Strength Concrete
Influence of Testing Procedure on the Shrinkage of a High-Strength ConcreteS
Full Paper: Ver trabalho ( inglês )  
S. B. SANTOS, A. S. Liduário, E. A. Gambale, M. A. S. Andrade

Abstract

Concrete shrinkage is both a simple phenomenon in regard to its manifestations a reduction of apparent concrete volume as well as a complex one when its causes are to be understood. As a consequence, the depiction of this phenomenon by means of tests generates behavioral doubts as to their results, as there is no single way of representing it. There are basically two ways of representing drying shrinkage: with and without immersion in the first 28 days after casting, stripping and test specimen curing.
This study aims to evaluate the effects caused in drying shrinkage by the immersion cure of high-strength concrete (HSC) in a saturated solution of water and lime as referred to in ASTM C157, and for the same high-strength concrete mixture performed without solution immersion. The purpose is to compare both test results and study their applicability and restrictions.
Finally, a further aim is to verify how the procedures for measuring shrinkage strains may influence the results, since mechanical reading equipment was used with of pins set into the test specimens, as well as an electrical Carlson strain meters.
These investigations are part of a future evaluation of test procedures designed and performed by the Concrete Laboratory of Furnas Centrais Elétricas S.A, based in the state of Goiás, Brazil, which may become the focus of a future change in the Mercosul Standard - NM131 and therefore an improvement of the test and its possible interpretations.

Keywords: Autogenous Shrinkage; Drying Shrinkage; High-Strength Concrete; Tests.




Copyright © 2006 IBRACON. All rights reserved.

Multivariate Analysis of the Variables Influencing the Form of the Chloride Profile in Reinforced Concrete Structures Exposed to a Tropical Marine Climate
Análisis Multivariado de las Variables que Influyen en la Forma de los Perfiles de Concentración de Cloruro en Estructuras de Hormigón Armado Expuestas a un Clima Tropical Marino

Full Paper: Ver trabalho ( inglês )   Trabalho Completo: Ver trabalho ( inglês ) 
I. G. SEIGLÍE, E. J. PÉREZ-GARCÍA, P. CASTRO-BORGES

Abstract

Chlorides coming from the marine breeze are the main cause of corrosion and deterioration of the structures in marine environment.
On the other hand, the interpretation of their concentration profile is an important tool to predict future behavior of the structure and to take preventive/corrective actions. Such profiles are commonly interpreted through mathematical tools and the exposure environment is one of the heaviest variables in the resulting predictions. Because of the complexity of the species transport phenomena associated to the predictions, there is no enough consensus when explaining results obtained under different circumstances and materials.
The multivariate analysis is applied in this work as a tool to validate the interpretation of the form of the chloride concentration profile of concrete as well as to show its dependency with several parameters such as the direction and incidence of dominant winds, the blocking to the marine breeze and the wet and dry process in the substructure of the Turigüanó.Cayo Coco viaduct bridges.
An association of the different variables in groups allowed obtaining a dendogram that confirmed: more influence of chloride penetration in the elements located to the East side, and in coincidence with the dominant winds; the existence of a peak in the
concentration profile of the closest external beams¨ parts that would be associated to the wet and dry process of the elements; the existence of a blocking to the marine breeze that promotes lesser affection by the chlorides in the central beams and North sides from the bridges than on other parts.

Keywords: Chloride, corrosion, concrete, marine environment, multivariate analysis.


Resumen

Los cloruros provenientes de la brisa marina son la principal causa de corrosión y deterioro de las estructuras en ambientes marino.
El estudio e interpretación de sus perfiles de penetración son valiosas herramientas para predecir el comportamiento futuro de la estructura y tomar medidas preventivas/correctivas. Dichos perfiles son comúnmente interpretados a través de herramientas matemáticas, siendo el ambiente de exposición una de las variables con mayor peso en las predicciones Dada la complejidad de los fenómenos de transporte asociados a la predicción no existe aún consenso al momento de explicar los resultados obtenidos bajo circunstancias y materiales diferentes.
Este trabajo aplica el análisis multivariado como una herramienta para validar la interpretación de la forma del perfil de concentración de cloruros del hormigón y demostrar la dependencia de la dirección e incidencia de los vientos, del apantallamiento y del proceso de mojado y secado en la estructura de los puentes del Pedraplén Turiguanó Cayo Coco.
Se obtuvo un dendograma, en el que se asocian las diferentes variables en grupos, que permitió confirmar: que los elementos ubicados al lado Este, coincidentes con la dirección de los vientos predominantes, se encuentran mas afectados por la penetración del ion cloruro; la existencia de un pico en los porcentajes de cloruros cercanos a la cara exterior de las vigas, que pudiera estar asociado al efecto de mojado y secado en los elementos; la existencia de un efecto de apantallamiento que provoca que las vigas centrales y el lado norte de estos puentes estén menos afectados por el ion cloruro.

Palabras-clave: Cloruros, corrosión, hormigón, ambiente marino, análisis multivariado.



Copyright © 2006 IBRACON. All rights reserved.
Comparative Assessment of Self-Compacting Concretes with and without Viscosity Modify Admixture
Comparação de Propriedades de Concretos Auto-Adensáveis com e sem Aditivo Modificador de Viscosidade
Full Paper: Ver trabalho ( inglês )   Trabalho Completo: Ver trabalho ( inglês )   
B.F. TUTIKIAN, R.A. CREMONINI, D.C.C. DAL MOLIN

Abstract

This paper aims to contribute to decisions concerning the use of viscosity modifying agents (VMA), which can be used as a
partial substitute for fines, the elements responsible for increasing the resistance to segregation of self-compacting concrete
(SCC). In this study, samples of SCC were prepared with and without the addition of a VMA using the mix design method
proposed by Tutikian [1]. It was observed that the addition of a VMA increased compressive strength and in some cases
also lowered chloride ion penetration within the same range of compressive strength values. It was also observed that the
increased cost resulting from the use of a VMA was compensated by the use of a poorer mix, with similar strength levels

Keywords: viscosity modify admixture (VMA), self-compacting concrete (SCC), cost, design diagram, ion chloride
penetration.


Resumo

Este trabalho pretende dar uma contribuição para a tomada de decisão do uso dos aditivos modificadores de viscosidade
(VMA), já que este componente substitui parcialmente os finos, responsáveis pela resistência à segregação do concreto
auto-adensável (CAA). Foram dosados CAA com e sem a presença do VMA, através do método de dosagem proposto por
Tutikian [1]. Observou-se que o VMA aumentou as resistências à compressão e diminuiu, em alguns casos, a penetração
de íons cloretos, para a mesma faixa de resistência à compressão. Observou-se, também, que o aumento de custo
provocado pelo aditivo foi compensado pela utilização de traços mais pobres, com os resultados finais similares.

Palavras-chave: aditivo modificador de viscosidade (VMA), concreto auto-adensável (CAA), custo, diagrama de dosagem,
penetração de íons cloretos.


Copyright © 2006 IBRACON. All rights reserved.
 
 
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