Abstract Civil construction is an industry sector that has been used as an outlet for the reuse of industrial waste. The present work aims to use the residue of Ethylene Vinyl Acetate (EVA) from the footwear industry as a partial substitute for a granulometric range of aggregates, aiming at the production of structural concrete and application to industrial floors. The proposed mixing ratios were evaluated from uniaxial compression, three-point bending, and drying shrinkage tests. The results of the uniaxial compression tests showed that the concrete with EVA addition still has enough strength to be considered structural concrete. In addition, the EVA and polypropylene fiber particles act as stress transfer bridges in the cracked zone, resulting in an increase in residual stresses and, consequently, in the toughness of the concrete in the three-point bending test. Finally, Technical Report 34 was used as a procedure to design an industrial floor based on the compressive strength, Young's modulus, and flexural behavior of the tested composites. The final result showed that even with lower compressive strength, fiber-reinforced concrete with EVA achieves greater structural efficiency for an industrial floor with the same cross-sectional height as ordinary fiber-reinforced concrete.

Resumo A construção civil é um setor da indústria que tem sido utilizado como uma saída para o reaproveitamento de muitos resíduos. O presente trabalho visa utilizar o resíduo de Etileno Vinil Acetato (EVA) da indústria calçadista como substituto parcial de uma faixa granulométrica de agregados, visando produção de concreto estrutural e aplicação a concretagem de pisos industriais. As proporções de mistura propostas foram avaliadas a partir de ensaios de compressão uniaxial, flexão em três pontos e retração por secagem. Os resultados dos testes de compressão uniaxial mostraram que o concreto com substituição ainda apresenta resistência suficiente para ser considerado concreto estrutural. Além disso, as partículas de EVA e da fibra de polipropileno funcionam como pontes de transferência de tensões na zona fissurada, resultando em um aumento das tensões residuais e, consequentemente, da tenacidade do concreto no teste de flexão em três pontos. Por fim, o Technical Report 34 foi utilizado como procedimento para dimensionar um piso industrial a partir da resistência a compressão, módulo de Young e comportamento a flexão dos compósitos ensaiados. O resultado final mostrou que mesmo com menor resistência à compressão, o concreto reforçado com fibras e substituição parcial de EVA consegue maior eficiência estrutural para um piso industrial de mesma altura de seção transversal que o concreto reforçado com fibras comum.

ABSTRACT Besides the strength enhancement and strain improvement (strain-hardening behavior), the use of natural fibers as reinforcement in cement-based matrices can also be highlighted as an economical and eco-friendly alternative for the future of the construction industry. In the present work, cement-based composites reinforced by natural sisal fibers were produced and tested under direct tensile loading. The Portland cement was partially replaced by pozzolans (metakaolin – MK and fly ash – FA), aiming to produce a calcium hydroxide-free matrix to ensure the durability of the fibers. The natural sisal fibers were used in a 5% volume fraction (in mass), divided into three layers. The mechanical properties of composite plates were compared to other literature results and demonstrated to be compatible with recent research. The crack pattern was analyzed by Digital Image Correlation (DIC) for a better understanding of their failure mechanisms. The material presented a tensile strength increase after the first crack formation, marked by multiple cracking partners from this point. Finally, a comparison between direct (LVDTs) and indirect (DIC) methods of strain measurement was done and demonstrated minor results for the DIC, approximately 84% of those obtained from the LVDTs.

resumo: Como solução para o esgotamento dos recursos naturais e o enorme desperdício gerado pela indústria da construção civil, o uso de agregado reciclado graúdo tornou-se uma tendência em muitos países. Os resíduos de construção e demolição são heterogêneos e compostos principalmente por detritos de concreto e cerâmicos. O processo de reciclagem geralmente envolve não apenas trituração e peneiramento, mas também técnicas avançadas para separar essas duas frações. Esses processos são caros e frequentemente ineficazes. Embora a maioria dos estudos e normas internacionais se concentrem apenas em agregados reciclado de concreto para uso estrutural, é possível obter características semelhantes utilizando-se agregados reciclados mistos com uma fração cerâmica de até 20%. Essa iniciativa pode diminuir os custos de reciclagem e torná-la mais viável. Portanto, este trabalho apresenta uma investigação experimental de um agregado reciclado brasileiro, que foi separado em três frações: agregado reciclado misto, de concreto e cerâmico. As análises mostraram que o agregado reciclado misto possui propriedades geométricas, físicas e mecânicas semelhantes ao agregado reciclado de concreto. Além disso, o concreto fabricado com 20% de agregado reciclado misto apresentou uma redução de apenas 0.6% na resistência máxima à compressão e 36.8% no módulo de elasticidade em comparação com o concreto fabricado com a mesma quantidade de agregado reciclado de concreto.

abstract: As a solution to the high depletion of natural resources and huge waste generated by the construction industry, the use of coarse recycled aggregate has become a trend in many countries. The construction and demolition waste is heterogeneous and mostly composed of concrete and masonry debris. The recycling process usually involves not only crushing and screening but also advanced techniques to separate these two fractions. These processes are costly and most frequently ineffective. Although most studies and international standards focused only on recycled concrete aggregate for structural use, it is possible to achieve similar characteristics with mixed recycled aggregates that have a ceramic fraction of up to 20%. This initiative can decrease recycling costs and make it more feasible. Therefore, this work presents an experimental investigation of a Brazilian recycled aggregate, which was separated into three fractions: mixed, concrete, and masonry aggregates. The analyses showed that the mixed recycled aggregate displayed geometric, physical, and mechanical properties similar to the recycled concrete aggregate. In addition, concrete made with 20% of mixed recycled aggregate presented a reduction of only 0.6% in maximum compressive strength and 36.8% in the modulus of elasticity compared with concrete made with the same amount of recycled concrete aggregate.

Resumo Em virtude da necessidade de estudo a respeito da capacidade residual do concreto após situações de altas temperaturas, este trabalho apresenta o uso da metodologia do planejamento experimental fatorial com configuração estrela, formalmente denominado de delineamento composto central rotacional (DCCR), para o estudo da resistência à compressão de corpos de prova de concreto aquecidos em fornos. Com essa ferramenta, foram analisadas conjuntamente as variáveis relação água/cimento e temperatura, tomadas em cinco níveis distintos cada uma, conforme metodologia estatística predefinida. São utilizados ainda ensaios de termogravimetria que permitem comprovar os distintos níveis de dano para diferentes pontos da seção transversal e o efeito da carbonatação e reidratação no concreto. Além disso, foi detectada a existência de uma zona intermediária para qual a temperatura proporciona um incremento dos produtos de hidratação, permitindo a discussão da proteção de estruturas de concreto por meio do controle da relação água/cimento.

Abstract Motivated by the need for studies on the residual capacity of concrete after high temperature situations, this research study presents the use of the experimental design planning methodology with star configuration, formally denominated central composite rotatable design (CCRD), to study the compressive strength of concrete specimens heated in ovens. With the use of this tool, the variables water/cement ratio and temperature were analyzed together, taken each at five different levels, according to a predefined statistical methodology. We also used thermogravimetric tests that allow verifying the different levels of damage for different points of the cross section and the effect of carbonation and rehydration on the concrete. In addition, the study detected the existence of an intermediate zone at which the temperature increases the production of hydration products, leading to a discussion about the protection of concrete structures by controlling the water/cement ratio.

Geopolymers may be described as solid and stable synthesized aluminosilicate materials, whose properties are generally believed to provide a superior durability behavior. The work in hand presents the results of an experimental investigation on the thermomechanical behavior of geopolymer matrices composed by metakaolin (MK), silica fume (SF) and blast furnace slag (BFS). The alkaline activator solution consisted of sodium silicate and sodium hydroxide. The use of different aggregates was also investigated, by replacing natural sand with chamotte. Samples were submitted to different temperatures at predetermined intervals to a maximum of 1000ºC. Compression tests were performed, before and after the exposure to elevated temperatures. X-ray diffraction, thermal analysis (TGA and DTA) and scanning electron microscopy (SEM) were used to investigate the microstructural characteristics of the studied materials. The results showed that the presence of BFS in the geopolymer mixture significantly increases its mechanical response. However, the incorporation of SF presents inferior behavior in regular conditions and when exposed to elevated temperatures. The replacement of sand with chamotte results in higher compatibility above 500ºC, when a better tolerance to extreme environmental temperature conditions was observed.

O uso simultâneo de diferentes tipos de fibras como reforço em concretos, pastas ou argamassas, está diretamente associado ao combate da propagação de fissuras em diferentes estágios do seu comportamento carga-deflexão ou tensão-deformação. O objetivo do presente artigo é avaliar o comportamento à flexão, no nível material e estrutural, de concretos autoadensáveis reforçados com meso e macrofibras de aço. Dois ensaios foram utilizados, visando a caracterizar, mecanicamente, os concretos reforçados com frações volumétricas de 1 e 1,5% de fibras híbridas de aço: resistência à flexão em quatro pontos (nível material) e resistência à flexão em painéis circulares de concreto (nível estrutural). Os resultados obtidos indicaram que a hibridização do reforço fibroso elevou o estado-limite de utilização dos concretos, contribuindo para o aumento da tenacidade e da capacidade de carga para pequenos níveis de deslocamento e aberturas de fissura. Tais benefícios se mostraram mais evidentes nos ensaios estruturais, tendo em vista o grau de hiperestaticidade e o potencial de múltipla fissuração dos painéis. No ramo descendente das curvas carga-deslocamento, quando macrofissuras eram predominantes, as macrofibras mostraram-se mais eficientes, aumentando a capacidade global de absorção de energia dos compósitos.

The simultaneous use of different types of fibers as reinforcement in concrete, mortar or pastes, can avoid the propagation and widening of cracks at different stages of their load-deflection or stress-strain behavior. The purpose of this article is to evaluate the flexural behavior in the material and structural scale of self-compacting concretes reinforced with meso and macro steel fibers. Two tests were used to mechanically characterize the concretes reinforced with volume fractions of 1 and 1.5% hybrid steel fibers: four point bending tests (material scale) and round panel tests (structural scale). The results indicated that hybridization of fiber reinforcement raised the serviceability limit state of concrete, contributing to increased toughness and load bearing capacity for small levels of displacement and crack openings. Such benefits were more evident in the structural tests considering the degree of hyperstaticity and multiple cracking potential of the panels. In the descending branch of the load-displacement curves, where macro-cracks were predominant, macro-fibers were more efficient in increasing the overall capacity for energy absorption of the composites.

Durable sisal fiber cement composites reinforced with long unidirectional aligned fibers were developed and their mechanical behavior was characterized in a multi-scale level. Tensile tests were performed in individual sisal fibers. Weibull statistics were used to quantify the degree of variability in fiber strength at different gage lengths. The fiber-matrix pull-out behavior was evaluated at several curing ages and embedded lengths. The composite's mechanical response was measured under direct tension while crack formation was investigated using a high resolution image capturing procedure. Crack spacing was measured using image analysis and correlated with the applied strain under both the tensile and bending response.