resumo: O cimento Portland continua sendo o principal material de escolha na construção civil, devido às suas propriedades térmicas, mecânicas e de durabilidade. No entanto, há uma crescente preocupação com a grande quantidade de energia consumida e a poluição ambiental gerada durante sua produção. Dessa forma, a presente pesquisa buscou avaliar o potencial do material residual fino produzido pela britagem de rochas basálticas através da ativação alcalina, para formar uma matriz cimentícia suplementar. O pó do basalto com tamanho de partículas menor que 53μm foi preparado e ativado com solução de hidróxido de sódio, tendo como coadjuvante a solução silicato de sódio. O material também teve o processo de cura realizado em 5 níveis de temperatura, 74,8, 85, 100, 115, 125,2°C conforme o delineamento experimental. Depois de curado o material teve a resistência à compressão avaliada, atingindo valor médio de 10,21 MPa para a mistura H5S15T125. A análise da microestrutura foi realizada através da microtomografia de raios X, apresentando a reconstrução dos poros e fissuras presentes internamente, concluindo que temperaturas de cura mais altas formaram matrizes mais porosas, embora com mais resistência. A partir dos dados coletados foi realizada a análise estatística do planejamento apresentando que hidróxido de sódio e a temperatura apresentam efeito estatisticamente significativo na variável resposta resistência à compressão. Portanto, é possível através da álcali-ativação do pó de basalto produzir um material cimentício de resistência moderada, dando finalidade ao resíduo e diminuído a emissão de partículas nocivas à atmosfera.

resumo: Portland cement remains the main material of choice in construction due to its thermal, mechanical and durability properties. However, there is growing concern about the large amount of energy consumed and the environmental pollution generated during its production. The objective of this study, therefore, was to evaluate the potential of the fine residual material produced by crushing basalt rocks to form a supplementary cementitious matrix through alkaline activation. Basalt powder with a particle size of less than 53µm was prepared and activated with a sodium hydroxide solution, with a sodium silicate solution as an adjuvant. The curing process of the material was also carried out at 5 temperature levels, 75, 85, 100, 115, 125°C, according to the experimental design. The paste was dry curing at a standard digital laboratory oven for 24 hours. After curing, the compressive strength of the material was evaluated, reaching a mean value of 10.21 MPa for the H5S15T125 mixture at 28 days. The microstructure analysis was performed by X-ray microtomography, presenting the reconstruction of the internal pores and cracks, leading to the conclusion that higher curing temperatures formed more porous matrices, although with more strength. Based on the collected data, the statistical analysis of the design was performed showing that sodium hydroxide and temperature have a statistically significant effect on the response variable compressive strength. As such, the alkali-activation of basalt powder can potentially produce a cementitious material of moderate strength, giving purpose to the residue and reducing the emission of harmful particles into the atmosphere.

Resumo Nanotubos de carbono (NTCs) são potenciais candidatos a melhorar o balanço térmico do concreto, reduzindo as tensões internas causadas pelo aquecimento diferencial em elementos maciços de concreto. Quanto maior a relação de aspecto (RA) e o teor de NTCs, maior será a condutividade térmica (CT) esperada. Porém, uma RA elevada pode prejudicar a dispersão adequada do NTCs na matriz cimentícia, potencialmente prejudicando a trabalhabilidade e resistência mecânica do compósito. Este estudo avaliou o efeito do RA (35, 250, 900 e 3500) e teor (0,05% e 0,10%) de NTCs na CT, reologia (squeeze flow) e resistência mecânica das pastas de cimento. Os resultados mostraram que a incorporação de 0,05% NTC aumentou a CT da pasta em até 15% para uma RA de 250, mas o aumento da RA reduziu progressivamente a CT do compósito. Por sua vez, a incorporação de 0,10% NTC não resultou em ganhos significativos de CT. A tensão de escoamento e a viscosidade das misturas aumentaram progressivamente com o aumento do teor de NTC e da RA, em até 119% em comparação com a pasta de cimento sem NTCs. Nenhuma diferença significativa foi observada na resistência à compressão de 28 dias com incorporação de 0,05% NTCs, enquanto 0,10% NTCs levou a pequenas reduções de resistência para algumas misturas. Em relação à resistência à flexão, a incorporação de 0,05% de qualquer um dos NTCs diminuiu a resistência das misturas, enquanto a incorporação de 0,10% geralmente compensou essa redução, exceto pela RA mais baixa. No geral, os NTCs com RA intermediária (~250) foram eficazes em melhorar a condutividade térmica da pasta de cimento, aumentando-a em 15% com teor relativamente baixo (0,05%), enquanto não prejudicou significativamente o desempenho fresco e mecânico do compósito.

Abstract: Carbon nanotubes (CNTs) are potential candidates to enhance the heat balance of concrete, reducing internal stresses caused by differential heating in massive concrete elements. The higher the aspect ratio (AR) and content of CNTs, the greater the expected thermal conductivity (TC). However, high AR may impair the proper dispersion of CNTs in cementitious matrix, potentially harming the workability and mechanical strength of the composite. This work evaluated the effect of the AR (35, 250, 900, and 3500) and content (0.05% and 0.10%) of CNTs on the TC, rheology (squeeze flow), and mechanical strength of cement paste. Results showed that 0.05% CNT increased the TC of paste by up to 15% for AR of 250, but further increasing AR progressively reduced the TC of the composite. In turn, 0.10% CNT incorporation did not result in significant TC gains. The yield stress and viscosity of the mixes progressively increased as CNTs content and AR increased, by up to 119% compared with plain cement paste. No significant differences were observed in 28-day compressive strength with 0.05% CNT incorporation, while 0.10% CNT led to slight strength reductions for some mixes. Regarding flexural strength, 0.05% incorporation of either CNT decreased the strength of the mixes while 0.10% incorporation generally compensated this reduction, except for the lowest aspect ratio. Overall, CNTs with intermediate AR (around 250) was effective in improving the thermal conductivity of cement paste, increasing it by 15% with relatively low content (0.05%) while did not significantly impair the fresh and mechanical performance of the composite.

Civil construction is one segment responsible for major environmental and social impacts. Among its raw materials, Portland cement, which is produced by the burning and subsequent grinding of a composition of clays and limestones. This manufacturing process causes great environmental damage, both by the exploitation of deposits and by the process of clinkering (burning of raw materials), which emits a significant amount of CO2 in the atmosphere. Therefore, there is a need for research on materials that reduce these impacts on the environment and that can be used by civil construction to the partial replacement of cement. Thus, this research had as objective to produce settlement mortar through the partial replacement of the Portland cement by filler powder, in different proportions and to study its mechanical properties. The results show that the partial replacement of the cement by the residue has acceptable behavior in the mortar.

ABSTRACT This work describes the second of a series of studies of the effects of injection molding conditions on the mechanical and thermal properties of Polyamide 6/Glass Fiber/Montmorillonite (PA6/GF/MMT) composites and was motivated by the lack of information about how the processing variables influence on the properties of three-phase composites containing fiber glass. By this time, the effects of the injection molding temperature associated with the fiber glass percentage on the mechanical and thermal properties of the composite are investigated. Some samples were processed, following a statistical experimental factorial planning, varying the mold temperature and the fiber glass percentage and maintaining 5 wt % of the MMT. The samples were submitted to tensile and flexural tests, XRD, SEM and DSC. The studies showed that an increase in the mold temperature and the fiber percentage improves the maximum tensile and flexural stresses. The increased mold temperature slows the cooling rate, which, over time, decreases the degree of crystallinity. However, there is an increase in the intercalation of the polymeric chains and the nanoclay lamellae, and the structure forms with fewer defects.