Eliana Cristina Barreto Monteiro

Durability Indicators Comparison for SCC and CC in Tropical Coastal Environments

Self-compacting concrete (SCC) demands more studies of durability at higher temperatures when subjected to more aggressive environments in comparison to the conventional vibrated concrete (CC). This work aims at presenting results of durability indicators of SCC and CC, having the same water/binder relations and constituents. The applied methodologies were electrical resistivity, diffusion of chloride ions and accelerated carbonation experiments, among others, such as microstructure study, scanning electron microscope and microtomography experiments. The tests were performed in a research laboratory and at a construction site of the Pernambuco Arena. The obtained results shows that the SCC presents an average electrical resistivity 11.4% higher than CC; the average chloride ions diffusion was 63.3% of the CC; the average accelerated carbonation penetration was 45.8% of the CC; and the average open porosity was 55.6% of the CC. As the results demonstrated, the SCC can be more durable than CC, which contributes to elucidate the aspects related to its durability and consequent prolonged life cycle.

Influence of Water-Cement Ratio and Cover Thickness on Chloride Extraction of Reinforced Concrete

Chloride ions can infiltrate concrete by a variety of ways, including admixtures, contaminated sand, or external penetration. When the concentration of chloride ions reaches a critical level, the corrosion begins. This article reports on a study that evaluated the method of electrochemical extraction of chloride ions for the rehabilitation of concrete structures with reinforcement corrosion. The authors investigated the influence of the concrete cover and the water-cement ratio (w/c) in the efficiency of the method by determining the initial and the final chloride content. Electrochemical impedance spectroscopy and the corrosion potential were used to monitor the reinforcement electrochemical behavior during the chloride extraction. The test results verified that the method successfully extracted chloride ions. On average, 77% of the content of initial chloride ions at a distance of 0.5 cm from the surface (depth where the slices had been extracted) were removed. The study used tap water as the electrolyte, which caused high polarization of the reinforcing bars during the extraction; the authors recommend an alkaline solution for future studies. The porosity of the concrete was not affected by the electrochemical chloride extraction.

AVALIAÇÃO COMPARATIVA DO COMPORTAMENTO MECÂNICO DE CONCRETOS LEVES COM AR INCORPORADO

Este projeto apresenta o resultado dos estudos de dosagem para a producao de concretos leves com uso de aditivo incorporador de ar, tendo em vista seu crescente uso em aplicacoes como paredes de edificacoes habitacionais. Importantes aspectos a serem considerados com a incorporacao de ar foram as mudancas das caracteristicas mecânicas dos concretos em estudo tais quais absorcao, absorcao capilar, resistencia mecânica, dentre outras, quando com uso do aditivo incorporador. Observou-se que a incorporacao de ar, acarretou na reducao de massa especifica dos concretos e, alem disso, promoveu diminuicao das resistencias a compressao e o aumento da absorcao e absorcao capilar, o que possui relacao com os vazios presentes nos mesmos e que pode vir a influenciar no que diz respeito a durabilidade dos elementos de concreto. Observa-se que, a depender da classe de densidade do concreto, e importante avaliar a permeabilidade do mesmo como fator de se adotar medidas para reduzir efeitos deleterios

Analysis of a Concrete Structure that Was Exposed to Fires in the Metropolitan Region of Recife

In large cities, news about fires in buildings are powered by problems such as old wiring and no maintenance. Accidents with chemicals and human error, which when added to the different characteristics of each fire and structures can generate the factors causing these disasters. The gradual rise in temperature causes a different effect in mortar and concrete parts, verifying the change in coloring provided to loss of mechanical strength and surface crumbling, cracking and disintegration of the structure itself. This paper presents a case study in which a building that is located in the metropolitan region of Recife was exposed to a fire situation. The metropolitan region of Recife is composed of several old buildings that by virtue of their age may have delayed construction methods, and may expose the fragility of the concrete used in its construction on a fire situation. The concrete structures are recognized by the good resistance to fire because of the thermal characteristics of the material, however, the temperature rise in the concrete elements in characteristic causes a reduction in strength and modulus of elasticity of the material, the loss in stiffness leading to polyphase degradation of reinforced concrete, structural parts can lead to ruin, but when properly sized and executed, the concrete can serve as a proactive agent to be exposed to high temperatures, as the same may be subjected to high temperatures accidentally or they may be part of their normal work. Language: en