Paulo Helene

Improvement of physical and chemical properties of concrete with brazilian silica rice husk (SRH)

El uso de desechos industriales y agricolas como segmento en la produccion de cemento Portland ha contribuido de manera importante en la practica de desarrollo sustentable. El aumento en la demanda de cemento coincide con el uso de materiales aglomerantes suplementarios para minimizar el consumo de clinker. En este estudio, se informan los efectos de la sustitucion parcial de cemento Portland por silice extraido de la cascara de arroz (SRH) en hormigones con baja relacion agua/materiales cementicios. Las propiedades investigadas incluyen resistencia a la compresion, resistencia a la traccion, absorcion de agua por inmersion, absorcion de agua por capilaridad y resistencia a la penetracion de iones de cloruro. La investigacion indica que SRH es una adicion mineral eficaz para el diseno de hormigones durables que presenta una actuacion optima cuando la proporcion del reemplazo de cemento de Portland esta alrededor de 10%

Ensaio de migração de cloretos para concreto: influência do número de fatias extraídas

Chloride migration tests are used to measure the capacity of the concrete to inhibit chloride attack. Many researchers carry through this test in a slice of concrete extracted from the central part of cylindrical specimens, discarding about 75% of the concrete used to mold the specimens. This fact generated the question: would it be possible to extract more slices from a same specimen without losing the confidence in the results? The main purpose of this work is to answer to this question. Moreover, another aim of this study was to show the difference of chloride penetration between finished faces and the formwork surfaces of concrete beams and slabs. The results indicated that it is possible to use more slices of a single specimen for a chloride migration test. Moreover, it was demonstrated that significant difference of chloride penetration exists between the finished surface and the formwork surface of the specimens.

Previsão da vida útil de concreto armado de alta resistência com adição de metacaulim e sílica ativa em ambientes marinhos

In marine environments, the big problem related to concrete durability is a chloride ion attack. Service life prediction in this type of environment is still without consensus by technical and scientific researchers. This work presents advances by proposing a way to interpret data from chloride ions diffusion in high-strength concrete containing metakaolin and silica fume as admixtures. The results showed that metakaolin and silica fume increased service life in a marine environment by 240 per cent and 440 per cent, respectively. This evidenced the high efficiency of the metakaolin and silica fume admixtures as a way of producing more durable concretes for regions highly influenced by saltwater spray.

Surface treatment systems for concrete in marine environment: Effect of concrete cover thickness

There are some ways to extend the service life of a reinforced concrete structure. This paper focuses on the extension of the service life by treating the surface of reinforced concrete, specifically on the effect of the concrete cover thickness on the surface treatment system efficacy. Thus, chloride migration tests were performed and diffusion chloride coefficients were calculated. The service life of each case (treated or non-treated concrete) was estimated using these data and Ficks second law of diffusion. Results indicated that the thicker the concrete cover is, the greater the efficacy of the concrete surface treatment system will be. The dissemination of this information is important, since it is almost intuitive to think that the effect of a surface treatment system depends only on itself and this study shows the opposite.

Estruturas de Concreto. Contribuição à Análise da Segurança em Estruturas Existentes

The safety evaluation of an existing concrete structure differs from the design of new structures. The partial safety factors for actions and resistances adopted in the design phase consider uncertainties and inaccuracies related to the building processes of structures, variability of materials strength and numerical approximations of the calculation and design processes. However, when analyzing a finished structure, a large number of unknown factors during the design stage are already defined and can be measured, which justifies a change in the increasing factors of the actions or reduction factors of resistances. Therefore, it is understood that safety assessment in existing structures is more complex than introducing security when designing a new structure, because it requires inspection, testing, analysis and careful diagnose. Strong knowledge and security concepts in structural engineering are needed, as well as knowledge about the materials of construction employed, in order to identify, control and properly consider the variability of actions and resistances in the structure. With the intention of discussing this topic considered complex and diffuse, this paper presents an introduction to the safety of concrete structures, a synthesis of the recommended procedures by Brazilian standards and another codes, associated with the topic, as well a realistic example of the safety assessment of an existing structure.

Concreto submetido a vibrações nas primeiras idades

Este artigo traz informacoes sobre o comportamento nas primeiras idades de um concreto de alta resistencia, produzido com cimento de alta resistencia inicial, lancado e adensado em ambientes submetidos a vibracoes, como em obras de pontes de rodovias. Apresenta-se o programa experimental desenvolvido, descrevendo desde a moldagem dos corpos-de-prova, sob acao de vibracoes similares as induzidas pelo trafego, ate os ensaios de caracterizacao mecânica e de aderencia aco-concreto. Os resultados experimentais indicam que o concreto submetido a vibracao nas primeiras idades pode sofrer perdas na resistencia a tracao e no modulo de elasticidade. A reducao dessas propriedades pode comprometer a utilizacao da estrutura devido ao aparecimento de flechas e fissuras acima dos limites de norma. A reducao da resistencia a tracao do concreto deve ser considerada, tambem, na aplicacao de pavimentos rigidos, onde essa propriedade e fundamental para garantir a durabilidade do sistema. Nao foi observada nenhuma reducao na resistencia a compressao ou na capacidade de aderencia devido a introducao de vibracoes nas primeiras idades do concreto.

Self-healing of self-compacting concretes made with blast furnace slag cements activated by crystalline admixture

Test samples were examined using a specific crystalline admixture, AR glass fibre and three types of cements with percentages of blast furnace slag (BFS) of 55%, 35% and 0%. Test specimens were loaded under compression until 90% of their failure load, in order to generate a network of micro-cracks. These samples were subsequently immersed in lime water to trigger the self-healing mechanism, followed by various tests at 28, 56 and 84 days. As BFS content ratio was increased to 55%, there was a noticeable increase in mechanical recovery and permeation reduction properties, indicating good self-healing.

Response to the Discussion of “Concrete structures. Contribution to the safety assessment of existing structures, Rev. IBRACON Estrut. Mater. 2015, vol.8, n.5, pp. 744-748, proposed by Santos, D. M.; Stucchi, F. R. and Beck, A.T.”

Response to the Discussion of “Concrete structures. Contribution to the safety assessment of existing structures, Rev. IBRACON Estrut. Mater. 2015, vol.8, n.5, pp. 744-748, proposed by Santos, D. M.; Stucchi, F. R. and Beck, A.T.”

Estanqueidade de lajes de subpressão. Caso MIS-RJ

It is common in coastal cities as Rio de Janeiro, that buildings located close to the shoreline have their basements below water table level. In most cases, the engineering solution for these buildings is to design a massive anti-flotation slab to satisfy, principally, the issues related to structural dimensioning and calculation hypothesis. On the other hand, the execution of this solution imply in significant construction problems related to reinforced concrete watertightness and durability. This paper presents a case study about challenges and solutions devised to execute an anti-flotation, 1m thick, 1200m3 reinforced concrete slab for the new Museu de Imagem e Som (MIS) - Sound and Image Museum, located at 50m from the seashore, at Copacabana in Rio de Janeiro, RJ. The results show that concrete proportions, concreting plan and pouring method adopted were decisive in obtaining a watertight structure, avoiding thus the employment of traditional waterproofing alternatives.

A Review of the Application of Concrete to Offshore Structures

This paper presents a review of the application of concrete that has been used in offshore structures over 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 in the paper.