Antonio Domingues de Figueiredo

Workability Analysis of Steel Fiber Reinforced Concrete Using Slump and Ve-Be Test

This works present an experimental study addressing the workability of fiber reinforced concrete (FRC). Only conventional measurements, such as slump and Ve-Be test, were used to evaluate the effect of the fiber content in the mixture. The fiber content shows to be of great influence in the concrete mobility reducing the slump and increasing exponentially the Ve-Be time. The fibers act as a barrier to coarse aggregates movement reducing the materials mobility. So, increasing the aggregate size or the fiber aspect ratio the flowability of the material will be reduced. In order to reduce that effect, an increase in the mortar content and/or in the initial slump could provide better workability conditions. The results showed that the Ve-Be test is not applicable to concrete with plastic consistency. On the other hand, slump test could not be adequate for stiff concretes that will be consolidated by intense vibration.

Análise comparativa de comportamento mecânico de concreto reforçado com macrofibra polimérica e com fibra de aço

A utilizacao de macrofibras polimericas esta amplamente difundida no mercado brasileiro. Entretanto, a caracterizacao do comportamento mecânico de concretos reforcados com essas macrofibras ainda deve ser mais bem avaliada. Dentre os diversos metodos utilizados para essa finalidade, os ensaios realizados com sistema fechado de controle de velocidade de deslocamento fornecem resultados mais confiaveis. A principal vantagem conferida por esse sistema esta na avaliacao desses compositos em baixo nivel de fissuracao, com maior nivel de acuracia. O desempenho desses compositos foi estudado segundo uma norma recente (ASTM C1609 - 2010) e outra que e uma referencia tradicional no Brasil (JSCE-SF4 - 1984). Ambos os procedimentos prescrevem ensaios de flexao de corpos-de-prova prismaticos para determinacao da resistencia residual pos-fissuracao e da tenacidade. Foram estudadas duas fibras: uma macrofibra de polipropileno, nas dosagens de 0,22, 0,33, 0,50, 0,66, 0,82 e 1,0% em volume, e outra de aco, nas dosagens de 0,19, 0,32 e 0,45% em volume. Foi utilizada uma matriz de concreto com resistencia media a compressao de 35MPa. Foi verificado que a macrofibra polimerica pode proporcionar o mesmo nivel de resistencia residual que a fibra de aco, desde que sejam determinados teores com equivalencia de desempenho em estudo de dosagem. Alem disso, foi comprovada a maior precisao do ensaio utilizando-se a velocidade de deslocamento do corpo-de-prova como parâmetro de controle do ensaio, devido a reducao da instabilidade pos-pico, que propiciou melhor avaliacao da resistencia residual do composito nos niveis iniciais de deslocamento e fissuracao da matriz.

Mechanical Characterization of Synthetic Macrofibres

The present study proposes a methodology to characterize the mechanical properties of synthetic macrofibres, which are used as a reinforcement of new composites applied in civil construction industry. Some standards suggest that this characterization should be performed on original filaments and others propose using the current methodology used to characterise metallic fibres. These recommendations turn difficult the quality control procedure, so it was developed a methodology to characterize the mechanical properties of the macrofibres as they are supplied in the construction site, using the tensile test. In that sense, two types of macrofibres were evaluated obtaining their tensile strength and elastic modulus. Additionally, the macrofibres were mixed with aggregates in order to study how the abrasion affects their mechanical properties. Summing up, the proposed methodology is feasible, especially to estimate the tensile strength allowing its application in ordinary laboratories. Regarding the elastic modulus results, they may be underestimated using this method. Finally, it was observed that the abrasion between the macrofibre and the aggregates during the mixing process compromises the mechanical properties decreasing both the tensile strength and the elastic modulus.

Evaluation of concrete recycling system efficiency for ready-mix concrete plants.

The volume of waste generated annually in concrete plants is quite large and has important environmental and economic consequences. The use of fresh concrete recyclers is an interesting way for the reuse of aggregates and water in new concrete production. This paper presents a study carried out for over one year by one of the largest ready-mix concrete producers in Brazil. This study focused on the evaluation of two recyclers with distinct material separation systems, herein referred to as drum-type and rotary sieve-type equipment. They were evaluated through characterization and monitoring test programs to verify the behaviour of recovered materials (aggregates, water, and slurry). The applicability of the recovered materials (water and aggregates) was also evaluated in the laboratory and at an industrial scale. The results obtained with the two types of recyclers used were equivalent and showed no significant differences. The only exception was in terms of workability. The drum-type recycler generated fewer cases that required increased pumping pressure. The analysis concluded that the use of untreated slurry is unfeasible because of its intense negative effects on the strength and workability of concrete. The reclaimed water, pre-treated to ensure that its density is less than 1.03g/cm(3), can be used on an industrial scale without causing any harm to the concrete. The use of recovered aggregates consequently induces an increase in water demand and cement consumption to ensure the workability conditions of concrete that is proportional to the concrete strength level. Therefore, the viability of their use is restricted to concretes with characteristic strengths lower than 25MPa.

Barcelona Test as an Alternative Method to Control and Design Fiber-Reinforced Concrete Pipes

The use of fibers as primary reinforcement for concrete pipes (CPs) is known by both industrial and scientific researchers as an attractive alternative to steel. However, the use of fibers in CPs has not yet been well established in this industry because of, among other reasons, the lack of systematic quality control of fiber-reinforced concrete pipes (FRCPs). Therefore, an experimental program involving the production and testing of 600 mm (23.6 in.) internal-diameter FRCPs was performed using low contents of steel (10 and 20 kg/m3 [0.62 and 1.25 lb/ft3]) and polypropylene (2.3 and 4.6 kg/m3 [0.14 and 0.29 lb/ft3]) fibers. These FRCPs were expected to be viable alternatives to those unreinforced and steel bar-reinforced concrete pipes corresponding to low- to moderate-strength classes. A numerical simulation of the tests using the constitutive equation derived from the Barcelona test was carried out, aimed at confirming that both can be an innovative combination to deal with both the characterization of the FRC tensile behavior and the direct design of these pipes. In this regard, those pipes containing 20 kg/m3 (1.25 lb/ft3)of steel fibers reached the C60 strength class in the TEBT (equivalent to ASTM C76 Class I). Consequently, the steel bars could be completely replaced by fibers. This fact led to an effective reduction of 20% of steel as well as to the elimination of those operations related to the reinforcement preparation. Simultaneously, these FRCPs represent a challenge at a numerical level because the model could be insensitive to this low amount of fibers. The comparisons between the experimental and numerical results have confirmed the suitability of both the model and the constitutive equation to simulate the pipe response when subjected to the TEBT.

Avaliação do concreto reforçado com baixos teores de fibras para fins estruturais segundo a norma EN 14651-2007

RESUMO Dentre os diversos metodos de avaliacao do comportamento mecânico de concreto reforcado com fibras (CRF), o ensaio proposto pela norma EN 14651-2007 e um dos mais promissores. Isto ocorre porque o mesmo e base da nova proposta do fib Model Code para o dimensionamento de estruturas utilizando o CRF. Dado que nao ha normas tecnicas brasileiras abordando esse tipo de ensaio, e necessario empregar este metodo de ensaio na avaliacao do CRF. Para tal, um estudo experimental foi desenvolvido focando o uso deste metodo de ensaio para a qualificacao e dosagem de concretos reforcados com baixos teores de fibras de aco e de macrofibras polimericas. Foram realizados ensaios de flexao de corpos-de-prova prismaticos com entalhe na face inferior, cuja funcao e induzir o posicionamento da fissura. Foram estudados tres tipos de fibra, duas compostas de polipropileno (nas dosagens de 3,0, 4,5 e 6,0kg/m 3 – correspondentes a 0,33, 0,50 e 0,66% em volume, respectivamente) e uma de aco (nas dosagens de 15, 25 e 35 kg/m 3 – correspondentes a 0,19, 0,32 e 0,45% em volume, respectivamente) em uma matriz de concreto de resistencia a compressao media de 35MPa. Verificou-se grande estabilidade nos resultados dos ensaios, com baixa dispersao nos resultados. Foi comprovado que e possivel dosar as fibras de modo a atender diferentes niveis de requisitos estabelecidos no fib Model Code para o CRF destinado a aplicacoes estruturais quando sao considerados os valores medios dos resultados de ensaio. Esta situacao pode nao se repetir quando os resultados caracteristicos sao considerados. Palavras-chave: concreto reforcado com fibras, estruturas de concreto, metodo de ensaio, resistencia residual.

Avaliação da tenacidade de concretos reforçados com fibras através de ensaios com sistema aberto

The quality control of the structures elements produced with Fiber Reinforced Concrete (FRC) depends critically of a test method to control toughness that could be considered reliable, economical and compatible with existing design models. The usual control is mainly based on bending tests of beam specimens, requiring specific equipment rarely found in Brazilian concrete control laboratories. The simplified Barcelona test (EBS) appears as a promising alternative test for FRC, as it allows the extraction of sample and uses resources available in most laboratories. This study aims to compare results obtained with the EBS method and the bending of beams through JSCE-SF4, which is the most used in Brazil, seeking to establish correlations between the different responses of these test method. One type of steel fiber and another polypropylene fiber were used with three levels of consumptions. Five beams were molded for test JSCE-SF4 and eight cylinders were extracted from the prisms edges for the EBS. These methods resulted load versus displacement curves. The correlations were obtained by comparing the energy required to cause a crack width equivalent for both methods. The results showed that the open-loop system turns difficult to measure the residual strength (poscracking) at Serviceability Limit States (SLS). The EBS and JSCE-SF4 test methods are correlated in terms of residual strength and toughness. These correlations allow the use of either method without compromising the evaluation of these characteristics. EBS is an easier test method to perform and allows the evaluation of toughness in cores extracted in real structural elements.

IMPACTOS AMBIENTAIS E TOXICOLÓGICOS DA LIXIVIAÇÃO EM TIJOLOS CERÂMICOS COM ADIÇÃO DE RESÍDUOS: UMA REVISÃO BIBLIOGRÁFICA

A adequada destinacao de residuos e um dos topicos prioritarios no que tange a sustentabilidade ambiental, portanto, uma das praticas que vem sendo adotada e a de incorporacao destes residuos em tijolos cerâmicos. Estes materiais estao sujeitos a acao de mecanismos deleterios, como a lixiviacao que possui a capacidade de carrear elementos quimicos, podendo gerar riscos a saude humana e ao meio ambiente. Nesse contexto, o presente trabalho propoe avaliar a influencia do teor de incorporacao e a temperatura de queima nas concentracoes de elementos perigosos na solucao lixiviada de tijolos. A metodologia adotada consistiu da catalogacao de trabalhos cientificos publicados encontrados em bases de dados entre os anos de 2012 e 2017 e posterior analise dos resultados quanto a conformidade com as normas adotadas. De forma adicional, as propriedades de porosidade, absorcao de agua e resistencia mecânica a flexao foram correlacionadas em funcao da temperatura de queima e do teor de residuo incorporado. Os resultados demonstram que os tijolos com incorporacao de residuos sao capazes de manter dentro dos parâmetros normativos os teores materiais perigosos ou toxicos da solucao lixiviante. Alem disso, os resultados demonstram que ha influencia tanto do teor de incorporacao de residuo quanto da temperatura de queima nas propriedades dos tijolos com incorporacao de residuos.

New Test for the Characterization of the Tensile Constitutive Behaviour of FRC

Recently published fib Model Code 2010 has been an important step towards the use of fibre reinforced concretes (FRC) in structural applications. This guide has selected a beam test (EN 14651) for the characterization of tensile constitutive behaviour of RFC. One drawback of the EN test is that, because of their shape, it almost impossible to apply the test to specimens extracted from an in-situ existing element. Some new compact tests (with small size specimens) that overcome this difficulty have been recently proposed, like the wedge splitting test (WST), the Barcelona test, or the Double Edge Wedge Splitting (DEWS) Test. Despite the advances, issues are still present in the new tests. In this work, preliminary results of a research where presented focusing a new test for the determination of residual strength parameters. The test is based in the WST, but changes are made over the load device and the specimen, aiming to achieve simplifications that allow it to be used in routine quality verification. A more simple, fast, and economic test was obtained, which can be performed in a simple displacement controlled testing machine (with no need of close-loop control). In this paper, the test is introduced, and the friction coefficient assessed. It was shown that a stable friction coefficient (μ = 0.06) is obtained. This is a key aspect of the test, as the effective opening force applied to the sample is influenced by this value. Results suggest that this test is a potentially attractive, and should be explored to be used in routine control of the FRC.