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RESUMO Os materiais cimentícios de alto desempenho podem ser produzidos com a utilização de sílica ativa (SA) e de nanossílica (NS). Devido ao pequeno tamanho de suas partículas, esses materiais tendem a se aglomerar, diminuindo os seus potenciais reativos. Alguns pesquisadores estudaram métodos para dispersar essas partículas como ultrasonicadores e misturadores rotacionais, porém ainda é necessário realizar estudos sobre esses materiais, principalmente sobre o efeito da ultrasonicação da nanossílica coloidal. Dessa forma, esse estudo teve como objetivo avaliar o efeito da ultrasonicação (uso de ultrassom de alta energia) da sílica ativa e da nanossílica coloidal em pastas de cimento. Foram estudadas cinco pastas, sendo uma referência com 100% de cimento Portland CP V-ARI e as outras quatro substituindo 2% e 10% do cimento Portland por nanossílica coloidal e por sílica ativa, respectivamente, em seu estado natural e após a ultrasonicação. Foram realizados os ensaios de resistência à compressão, análise termogravimétrica (ATG), espectroscopia no infravermelho e porosimetria por intrusão de mercúrio (PIM) nas pastas. Os resultados mostraram que a utilização da NS coloidal em substituição ao cimento Portland aumentou a produção de C-S-H, o refinamento dos poros e a resistência à compressão das pastas, porém a utilização da SA em seu estado natural aumentou o tamanho dos poros e diminuiu o desempenho mecânico das pastas devido à aglomeração de suas partículas. Ao ultrasonicar a SA, houve maior produção de C-S-H, refinamento dos poros e maior resistência à compressão quando comparada com a pasta com SA sem o processo de ultrasonicação, comprovando a efetividade desse método para a dispersão dessas partículas. Apesar disso, a ultrasonicação da NS coloidal não resultou em diferenças significativas na microestrutura e de desempenho mecânico das pastas.

The ceramic coating systems applied to building facades have relevant aesthetic value and protection functions. The architectural and environmental conditions can greatly influence the degradation process of the facades, which may pose risks and compromise the durability and service life of the building and its components. The degradation process of facades changes according to the region where it takes place. To this end, the present study aims to determine damage intensity and distribution in the different regions of the facade. This study investigated the facades of three buildings that are part of the Materials Testing Laboratory (LEM) database of the Universidade de Brasilia. The degradation was quantified using a methodology proposed by Silva (2014) to generate a degradation index expressed in m 2. After the quantification of damages, few indexes associated with the percentage of degraded area, applied to the facade regions, are presented. These weighted indexes allowed to standardize the values observed in each region. Obtaining these indices is fundamental to the study of degradation. The results show that for a comparative analysis between the regions, the observed values should be corrected for the proportionality of the area of each region in relation to the total area of the facade. It was also noted that the continuous walls are the most affected regions, but they do not always present the highest damage intensity.

The microstructure of cement pastes is important to understand the effect of some parameters in the hydration process. In this context, this study had as objective to evaluate the effect of different water/binder (w/b) ratios in the hydration process of cementitious pastes produced with and without incorporation of silica fume and metakaolin. The pastes were obtained with water/binder ratios of 0.3, 0.4 e 0.5, with replacement, by weight, of Portland cement for silica fume and metakaolin, in the contents of 10% and 20%, respectively. It was performed the X-ray diffraction test of the pastes in the ages of 1, 3, 7, and 28 days, to evaluate the hydration evolution of the cementitious materials. According to the results obtained, it was observed that the cementitious pastes presented similar mineralogical phases, except for the pastes containing metakaolin due to the formation of new aluminate phases. With the increase of the water/binder ratio, the pozzolanic reactions and hydration occurred in greater proportion, standing out the metakaolin with greater reactivity.

Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC) is a material that combines the benefits of self-compacting concrete in the fresh state and the greater durability, with the gains of fiber- reinforced concrete in the hardened state, especially the gains in residual flexural strength. Results are presented in this paper of residual flexural strengths on 48 prenotched prisms conducted in accordance with RILEM TC 162 TDF for the Steel Fiber Reinforced Self-Compacting Concretes (SFRSCC). This article presents equations to estimate residual flexural stresses in SFRSCC. For this, SFRSCC prisms of two compressive strength classes, 20 MPa and 40 MPa, were produced with 3 different types of steel fibers with the contents volume of 0.5% and 1.0%. Based on the test results, equations were proposed to determine the residual flexural stresses established through regression analysis, which were, then, further validated with concretes produced in this work and results available in the literature. The equations found, despite showing an indication of the residual flexural strengths that will be achieved, obtained a relatively high error. In order for the equations to be applied in a technical way, further studies for a larger sample need to be carried out, seeking to optimize the equations.