Hormigón ligero con agregado reciclado de EVA para atenuación del ruido de impacto

The purpose of this study is to evaluate the acoustic performance of lightweight concrete with ethylene vinyl acetate copolymer (EVA) residues to reduce impact noise on floors. Three types of concrete with three different mix proportions were evaluated. The method adopted includes the characterization of water absorption, voids and density of the samples. The experimental study of noise impact followed the procedures of ISO 140. The results indicate that the lightweight concrete with EVA recycled aggregate can reduce impact noise levels by up to 15 dB and the highest percentage of coarse aggregate EVA does not entail a higher acoustic performance.La propuesta de este estudio consiste en la evaluación del desempeño acústico del hormigón ligero con residuos de ethylene vinyl acetate copolymer (EVA) para a reducción del ruido de impacto en pisos. Fueron evaluados tres tipos de hormigón con tres trazas diferentes. El método adoptado incluye la caracterización de la absorción de agua, del índice de vacíos y de la densidad en las muestras. El estudio experimental del ruido de impacto siguió las recomendaciones de ISO 140. Los resultados indican que el hormigón ligero con EVA reciclado puede reducir el nivel de ruido de impacto en hasta 15 dB y que el porcentaje más alto de agregado grueso de EVA no aumenta el desempeño acústico

Estudio del comportamiento mecánico del hormigón de ultra- altas prestaciones (UHPC) reforzado con fibras híbridas y con consumo reducido de cemento

This article evaluated mechanical behavior of ultra-high performance concrete (UHPC) reinforced with hybrid steel and polypropylene fibers, with cement consumption of 250 kg/m³ and application of confining pressure in fresh state. The consistency of the mixture was analyzed, as well as mechanical properties of compressive strength, flexural strength and toughness. The percentages of hybridization were 50 to 100% of metal fibers and 0 to 50% of polypropylene fibers. Results showed that the compressive strength of the composite was 180 MPa (26100 psi), despite its low cement consumption of 250 kg/m³ (2.08 lb/gal), with 80% steel fibers and 20% polypropylene fibers. The combination of fibers increased the mixture’s toughness. For the composition with 80% steel fibers and 20% polypropylene fibers, the strength for large deformations increased by 191% compared with the mixture with 100% steel fibers, pointing out the benefits of hybridization.En este trabajo se evaluó el comportamiento mecánico de los hormigones de ultra-altas prestaciones (UHPC) reforzados con fibras híbridas de acero y polipropileno, con un consumo de cemento de 250 kg/m3 y aplicando una presión de confinamiento en su estado fresco. Se analizó la consistencia de la mezcla, las propiedades mecánicas de las resistencias a la compresión y flexión, así como la tenacidad. Se usaron porcentajes de hibridación del 50 al 100% de fibras metálicas y de 0 al 50% de fibras de polipropileno. Los resultados muestran que la resistencia a la compresión del compuesto fue de 180 MPa (26.100 psi), a pesar de su bajo consumo de cemento, de 250 kg/m³ (2,08 lb/gal), con 80% de fibras de acero y 20% de fibras de polipropileno. La combinación de fibras incrementó la tenacidad de la mezcla. Para esta misma composición, la resistencia para las grandes deformaciones aumentó en un 191% en comparación con la mezcla que contenía un 100% de fibras de acero, demostrando así los beneficios de la hibridación

Self-compacting concretes (SCC): comparison of methods of dosage

The composition of a self-compacting concrete (SCC) should be defined to fulfills a number of requirements, such as self-compactibility, strength and durability. This study aims to compare three methods of dosage for SCC with local materials, so as to determine which one is the most economical and rational, thus assisting the executor in making a decision and enabling economic and technical feasibility for its application. The methods used in the experimental program were: Nan Su et al., which was developed in 2001 [1]; Repette-Melo, which was proposed in 2005 [2]; and Tutikian & Dal Molin, which was developed in 2007 [3]. From the results obtained in the experimental program, it was observed that the method which presented the lowest cost and highest compressive strength at the ages of 7, 28 and 91 days was Tutikian & Dal Molin, while the one which reached the lowest chloride ion penetration, best compactness and highest elasticity modulus was Repette-Melo. In tests carried out in the fresh state, all tested methods yielded mixtures which comply with the self-compactibility levels required by ABNT NBR 15823:2010 [4]

Comparativo das propriedades do concreto autoadensável (CAA) utilizando areia fina e cinza volante

O objetivo deste artigo é contribuir para a tomada de decisão sobre a definição do uso de materiais finos responsáveis pela resistência à segregação do concreto auto-adensável (CAA). Neste estudo, amostras de CAA foram dosadas com cinza volante, um material pozolânico, e areia fina, que é um material não pozolânico, utilizando o método de dosagem proposto por Tutikian & Dal Molin (2007) [1]. Foi observado que a utilização de cinza volante aumentou a resistência à compressão, principalmente nas idades mais avançadas, assim como os valores de módulo de deformação e velocidade das ondas de ultrasom. Também diminuiu a penetração de íons cloretos, para os mesmos valores de resistência em comparação com os CAA com areia fina e o custo final dos CAA com cinza volante foi inferior. Foram apresentados tanto os diagramas de dosagem como os de desempenho

Microstructure of concrete subjected to elevated temperatures: physico-chemical changes and analysis techniques

ABSTRACT The exposure of concrete to high temperatures, such as in a fire, leads to physical and chemical changes, which may cause deterioration of mechanical properties, cracking and spalling. This paper presents a critical review of microstructural changes in concrete exposed to high temperature. The transformations developed in the cement paste, aggregates and interfacial transition zone were studied, as well as the experimental techniques of microanalysis presented in recent related researches. Lastly, a critical analysis of experimental results from literature was performed. It was verified that microstructural changes are related to concrete properties and the heating process. The experimental techniques has a potential use for assessment of thermally damaged concrete, however, these techniques must be applied simultaneously and specific methods must be established