Uso da argila expandida e sílica ativa no melhoramento dos desempenhos mecânicos, físicos e térmicos de concretos leves estruturais

Abstract

A busca por materiais sustentáveis na construção civil, que apresentem menor massa específica, melhores desempenhos térmicos e manutenção das resistências mecânicas, representa grande desafio na produção e avaliação de concretos leves estruturais (CLE), o qual desponta como um material alternativo ao concreto convencional. Neste estudo realizou-se uma investigação para a confecção de concretos com alta resistência, baixa densidade e excelente desempenho térmico, com a finalidade de executar construções energeticamente eficientes. CLE foram estudados utilizando duas granulometrias de argila expandida (C 05 e C 15 ), onde houve a substituição do agregado graúdo pela C 15 em 0, 25, 50, 75 e 100%. Para promover a manutenção da consistência e resistência, utilizaram-se superplastificante (SPA) e sílica ativa (SA) nas misturas. Com base na metodologia utilizada, os concretos foram caracterizados física e mecanicamente, de acordo com as normas nacionais e internacionais vigentes. A densidade dos concretos, no estado endurecido, variou de 1.787 a 2.400 kg/m³ e, quanto a resistência à compressão, variou-se de 26 a 53 MPa, aos 7 dias de idade. O ensaio de condutividade térmica, por meio do método da placa quente protegida, foi realizado de acordo com a EN 12667, onde observou-se uma variação de 0,61 a 1,00 W/mK. Informações microestruturais da zona de transição interfacial (ZTI) entre agregado e matriz de cimento foram obtidas com a finalidade de analisar a relação com a resistência mecânica. A investigação revelou que, com a adição de argila expandida (C 05 e C 15 ) e SA nos concretos, houve a redução da densidade e da resistência mecânica, entretanto as características térmicas foram melhoras. Palavras-chave: materiais alternativos, concreto leve estrutural, densidade, resistência mecânica, condutividade térmica. ABSTRACTThe search for sustainable materials in civil construction, which presents a lower specific mass, better thermal performance and maintenance of mechanical resistance, represents a great challenge in the production and evaluation of structural lightweight concrete (SLC), which emerges as an alternative material to conventional concrete. In this study an investigation was carried out for the construction of concretes with high strength, low density and excellent thermal properties, in order to execute energy-efficient constructions. SLC were studied using two different granulometries of expanded clay (C 05 and C 15 ), where the coarse aggregate was replaced by C 15 at 0, 25, 50, 75 and 100%. To promote the maintenance of consistency and resistance, superplasticizer (SPA) and silica fume (SF) were used in the mixtures. Based on the methodology used, the concretes were physically and mechanically characterized, in accordance with current national and international standards. The density of the concretes, in the hardened state, ranged from 1,787 to 2,400 kg/m³ and, for compressive strength, ranged from 26 to 53 MPa at 7 days of age. The thermal conductivity test, using the protected hot plate method, was per...

Polymeric Waste from Recycling Refrigerators as an Aggregate for Self-Compacting Concrete

“…The results show that the replacement of natural gravel by PW significantly reduces the compressive strength and tensile strength of the concrete. This is in accordance with several studies in the same line of research and which showed a tendency to decrease resistance to axial compression with the incorporation of polymeric residues [11,37,[39][40][41][42][43][44][45].…”

“…As shown in Figure 10a, the specific gravity (ρ) of the SCC with PW decreases with the increase in the replacement of crushed stone by PW. Similar results for the specific gravity, absorption and void index were found in studies of [35,37]. The specific gravity tends to decrease because, according to [49], the density of the plastic aggregate in general is 70% lighter than the natural aggregate if you compare the specific gravity of the plastic aggregate used with the sand, 1.34 g/cm 3 to 2.61 g/cm 3 , respectively.…”

“…As shown in Figure 9, the dynamic elastic modulus (Ed) and static elastic modulus (Ec) of the SCC with PW tends to decrease as the content of the replacing gravel with PW increases. There was a decrease in the dynamic elasticity module by 1% for M5, 12% for M10, 5% for M15 and 58% for M20 and for the static module by 1% for M5, 13% for M10, 1% for M15 and 63% for M20; that is, the concrete becomes less rigid and these results are proportional to those found in the studies of [10,12,37,45]. This behavior can be explained by the incorporation of PW in concrete, which is a less rigid aggregate than natural gravel [46].…”

“…The most relevant characteristics that certainly must be taken into account to explain the behavior of SCC with PW is the surface roughness of the residue and its low specific gravity when compared to natural gravel, as well as its use in the form of particles to replace the natural coarse aggregate [37]. The PW has a smooth and polished surface compared to the natural gravel surface, which is rough and irregular.…”

“…Thus, the surface of the PW does not adhere properly with the mixing water and impairs the formation of the transition zone on the interface. The PW has a hydrophobic behavior, as rubber, and acts to reduce the concrete flow stress [37]. Images of the moment of execution of the tests in the fresh state are shown in Figure 5.…”