Self-cleaning surfaces have excelled in recent years in energy and environmental fields. In particular, in solar energy area, these surfaces are used to avoid soiling accumulation on photovoltaic (PV) modules. So far TiO 2 has been widely used due to its photocatalytic activity and photo-induced superhydrophilicity. However, this oxide has some limitations since it reduces the glass transmittance and it rapidly reestablish the water contact angle in dark environments. In order to circumvent these limitations, composites TiO 2 /SiO 2 have been proposed. For photovoltaic application, besides a good transparency in the wavelength region 300-1800 nm and self-cleaning properties, the coating should also present long durability and adequate adhesion to endure the outdoor conditions. Aiming at developing a coating with these properties, in this work, TiO 2 /SiO 2 composites containing different titanium content have been synthesized and compared with pure TiO 2 films in relation to adhesion, transparency and hydrophilicity. Both films have been deposited over low iron float glass substrates by sol-gel dipcoating technique and different calcination temperatures (400, 500, 600°C) and Si/Ti molar rates (Si 86 Ti 14 , Si 40 Ti 60 ) have been considered. TiO 2 /SiO 2 films showed higher transmittance in visible range compared with pure TiO 2 . TiO 2 /SiO 2 films showed superhydrophilic character before and after ultraviolet irradiation, with water contact angles near to 0°. Furthermore, as predicted, TiO 2 /SiO 2 films could keep the superhydrophilic character in dark environments, in contrast with pure TiO 2 films. Both TiO 2 and TiO 2 /SiO 2 films exhibited good adherence and it is shown that higher calcination temperatures and higher titanium content enhance such property. All films presented abrasion resistant property in contact with sponge and detergent. It has been demonstrated that high transmittance, self-cleaning and adherent composite has been obtained by a simple sol-gel route presenting good potential to be applied on photovoltaics systems.

The present study evaluated the mechanical behaviour of thin high-performance cementitious composite slabs reinforced with short steel fibres. For this purpose, slabs with 1%, 3% and 5% vol. of steel fibres were moulded using the slurry infiltration method. Fibres concentrated in the region subjected to traction during bending stresses. After curing for 28 days, all slabs underwent flexural testing. The slabs with 5% fibre showed significantly higher flexural strength, deflection and toughness compared to those of the control group without reinforcement. The dense fibre distribution, resulting from the production process, led to profiles with multiple random cracks in the region of failure of the slabs as the fibre content increased. The results of the statistical analysis showed the intensity of the correlation between the variables and revealed that the increase of the fibre content significantly influenced the parameters of mechanical behaviour (load, flexural strength, deflection, toughness and toughness factor). Images obtained by optical microscopy aided in understanding the fibre–matrix interface, showing the bonding surface between the constituents of the composite.

The work presents the characterization of clays from sterile mining of the concentrated phosphatic materials of Araxá in Minas Gerais as pozzolanic materials. Three clays of distinct tones, namely, yellow (YC), red (RC), and intermediate (IC) clays, were used at different levels of excavation depth. The clays were calcined at three temperatures (680, 760, and 840 °C) in a muffle-type electric oven. The pozzolanic activity levels of the calcined clays was measured through the conductivity change in saturated Ca(OH) 2 solutions and also from the result of the compressive failure load achieved by mortars with 35% of the Portland cement replaced with the calcined material. The results indicated that the calcined clays showed a high level of pozzolanic activity and can be used as a partial substitute for Portland cement, thus suggesting the possibility of recovering this sterile material.

Resumo A proteção passiva contra incêndio (PPCI) é um campo de estudo aplicado à indústria da construção civil. Os resíduos de tijolos refratários contêm elementos que podem contribuir para as propriedades necessárias à PPCI. Diante disso, o trabalho desenvolveu uma argamassa com resíduos de tijolos refratários para utilização como PPCI. As 4 formulações propostas tiveram a resistência à compressão e flexão, densidade e porosidade aparente, condutividade térmica e variação linear avaliadas antes e após tratamento térmico a 600 °C e a 1100 °C. A densidade não apresentou significativas diferenças entre as formulações. A porosidade aumentou após o tratamento térmico. A mistura que apresentou maior contração a 1100 °C foi aquela com maior teor de gesso e todas as demais apresentaram valores de contração menores que o máximo permitido pela C195. A proporção que utilizou maior quantidade de gesso foi o que obteve a menor condutividade térmica. Portanto, conclui-se que a utilização do resíduo refratário é viável para PPCI, uma vez que atendem aos requisitos normativos.

This work reports the main conclusions of a study on the mechanical behavior of concrete under ISO 834 fire with different cooling methods. The aim of this research was to provide reliable data for the analysis of structures damaged by fire. The experimental program used cylindrical concrete test specimens subjected to ISO 834 heating in a furnace up to maximum gas temperatures of 400, 500, 600, 700, and 800 °C. The compressive strength was measured in three situations: (a) at the different temperature levels reached in the furnace; (b) after a natural cooling process; and (c) after aspersion with water at ambient temperature. The results indicate that the concrete residual compressive strength is fairly dependent on the maximum temperature reached in the furnace and revealed that concrete of a lower strength preserved relatively higher levels of strength. The cooling method significantly influenced the strength, albeit at a lower intensity. In all cases, the residual strength remained in the range of 38% to 67% of the strength at ambient temperature. The statistical analysis showed that the data obtained by the experimental program are significant and confirmed the influence of the conditions imposed on the residual strength.

This paper presents an experimental evaluation of how variations in proposed parameters interfere with compressive strength resistance of mortar and concrete specimens. The results were obtained through laboratory tests in which samples were tested under varying conditions. These conditions were as follows: speed of load application (0.25, 0.50, 0.75, and 1.00 MPa/s), environmental conditions (saturated, 2 h dried, and 24 h dried specimens), curing (dry and wet), and specimen ends preparation (sulphur, neoprene, rectification, and without regularization). Comparisons were made on the basis of the compression strength resistance results and the coefficient of variation in order to analyse the homogeneity and dispersion among variables. It was found that in the case of capping, the best results were obtained by the rectification of concrete specimens. In the case of loading speed, the best results were obtained at a speed of 1 MPa/s. Dry curing showed the best results, even though not resulting in the highest resistance. The results for specimen conditions were in accordance with the expectations, with lower dispersion for saturated specimens.

No abstract