Aluísio Braz de Melo

Structural Integrity Assessment of Precast Concrete Slabs Employing Conventional and Recycled Coarse Aggregates via Vibration Tests

Precast slabs were tested, consisting of ceramic blocks supported by concrete ribs and with a concrete topping a few centimeters thick. These structures are very common in Brazil, being employed for the construction of houses and small buildings. In one of the tested slabs, recycled coarse aggregate was employed while conventional aggregate (granite gravels and quartz sand) was employed in the other tested slab. This study is part of a broader experimental programme which was designed to assess the applicability of concrete containing recycled aggregates as conventional aggregate replacement. In order to get insight into the structural behavior of slabs with recycled aggregates, the main focus of this paper is to assess the effect of structural load level on vibration parameters (Resonance Frequency, Damping Ratio and Transit Time). Full scale slab structural integrity was assessed by following changes in these parameters via a vibration (modal) test employing impact excitation. The structures were tested for several static load ratios (load to ultimate loading ratios (55%, 82% and 98%)). Visual inspection of induced cracking was also performed. The results obtained indicate a reduction of stiffness in both slabs up to 50% of the stiffness of the respective uncracked structure, which followed a similar trend despite the aggregate types. As for the damping ratios, the recycled aggregate containing slab showed lower values in comparison to the control slab with conventional aggregate. Whereas the former results might indicate similar load capacity, the latter, in principle, may have implications for the vibration serviceability limit state of structures. However, although structures with lower damping ratio can potentially present vibration problems, these studied elements are not often subjected to excessive vibration in its service life.

Desempenho estrutural de protótipo de alvenaria construída com blocos de terra crua estabilizada

Uma das dificuldades na difusao de tecnologias de construcao nao convencionais e a ausencia de informacoes tecnicas sobre os sistemas construtivos existentes. Exemplos de construcao eco-eficiente, em pequena escala, feita com blocos de terra crua, desenvolvidos pelo Prof. Roberto Mattone, do Politecnico di Torino, Italia, podem ser encontrados no Brasil, Italia e Argentina. Estes blocos feitos com prensa manual apresentam intertravamentos entre si que melhoram a resistencia e a rigidez da alvenaria. Testes em prototipos construidos com eles sao necessarios para atender as exigencias tecnicas e se obter credibilidade nas agencias governamentais financiadoras. Este artigo apresenta resultados referentes a avaliacao de desempenho estrutural de alvenaria (prototipo construido em escala real) feita com blocos de terra crua estabizada, mecânicamente por prensagem e quimicamente por adicao de cimento Portland. As avaliacoes de cargas de ocupacao e impactos na alvenaria foram realizadas atraves de ensaios de impactos de corpo mole e de corpo duro, solicitacoes transmitidas por fechamentos bruscos de porta e solicitacoes de cargas provenientes de pecas suspensas. A partir dos resultados pode-se afirmar que o prototipo apresentou desempenho satisfatorio em relacao a seguranca estrutural. Destaca-se que os blocos avaliados tem grande potencial para reduzir o impacto ambiental das edificacoes.

Pré-moldado (bloco EVAi) para alvenaria intertravada: projeto, produção, desempenho e simulação de uso em habitação social

A eficacia do projeto para habitacao social requer solucoes que contemplem os desempenhos tecnico e ambiental. Este artigo tem como objetivo abordar os conceitos de coordenacao modular e apresentar a proposta do bloco EVAi (Bloco Intertravados contendo Ethylene Vinyl Acetate), levando em consideracao avaliacoes de desempenho mecânico e termico com base em abordagens conceituais e experimentais. O bloco projetado nao possui funcao estrutural e tem dimensoes e geometria compativeis com alvenaria intertravada. A mistura de concreto leve foi otimizada para a producao dos elementos pre-moldados com incorporacao de residuos da industria de calcados local. O bloco EVAi traz melhorias ao processo produtivo, tanto pelo desempenho mecânico, leveza e geometria dos componentes como pelas dimensoes adequadas. O desempenho termico das alvenarias com blocos EVAi e melhor em relacao a paredes com tijolos cerâmicos convencionais. Alem disto, a geometria intertravada apresenta beneficios para o projeto de habitacao social em questao no tocante a ajustes usuais das dimensoes dos componentes em alvenarias, reduzindo o desperdicio. Comparacoes entre o sistema construtivo proposto e a tecnologia convencional ressalta a importância do partido arquitetonico como forca indutora para o avanco e disseminacao de novas tecnologias alternativas sustentaveis.

Study of EVA Blocks Waste Recyclability

The use of EVA (Ethylene Vinyl Acetate) waste, from shoes industry, in the production of pre-molded block (EVA block) has been researched in the last 12 years. The results have shown great potential for these wastes to be used as lightweight aggregate, to replace natural aggregate in the manufacture of bricks made of cement based composites. This article examines the potentiality of waste EVA blocks recyclability, as aggregate in the production of new EVA blocks. In the experiment EVA blocks were molded in the mix proportion of 1:5 in volume (20% of sand and 80% of EVA) and determined the mass and compressive strength at 28 days. Then the EVA blocks were crushed and resulting aggregate was reused in part (portion retained on a 4.8 mm sieve) in the molding of new EVA blocks, using in dosages two different proportions of crushed aggregate (50% and 70%, EVAr - waste of crushed EVA blocks) in relation to the total volume of coarse aggregate of original EVA (EVA - waste from shoes industry). The average compressive strength at 28 days of the original EVA block was 1.2 MPa, whereas the block EVAr70 was 2.2 MPa and the block EVAr50 was 1.7 MPa. Thus, there was an 83% increase in the compressive strength on the block EVAr70 and 44% on the block EVAr50. It was also noticed there was no significant difference among the weights of all the blocks produced. So, it appears that the EVAr aggregate impacted more in the compressive strength than in the mass of the blocks. Thus, the recyclability of the EVA block appears viable.