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The present paper studied the influence of nanosilica dispersed on superplasticizer, and its combined effect with silica fume, on different concrete properties. Compressive strength, tensile strength by diametrical compression and water absorption by capillarity tests, as well as accelerated durability tests against chloride ions were carried out....
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... mean values of results obtained from compressive strength at the ages of 1, 7 and 28 days and 28-day tensile strength by diametrical compression tests are presented in Figures 3 and 4, respectively. Results indicated that 0.5% nanosilica addition to concretes (C-0.5-0) induce a 9.6% and 7.1% increase in 7-day and 28-day compressive strength compared to reference concrete (REF), respectively. When combining nanosilica with silica fume, it is noticed that in early ages REF reached a higher compressive strength. However, at 28 days, the concretes C-0.5-10 and C-0.7-10 reached 76.0 MPa and 77.7 MPa, respectively, while REF reached 70.2 MPa. The greatest resistance gain at 28 days, and even at 90 days, was also observed by other researchers (Senff et al., 2010;Joshagani;Moeini, 2017). Evidences of a synergistic effect between these additions was not observed, since when adding silica in the mixture, for the same content of nanosilica (C-0.5-0 and C-0.5-10) there were no compressive strength gains. Differently from that observed by Li et al. (2017a), who found that addition of 2% powder nanosilica caused a 17% increase in 28-day compressive strength, whereas at 10% silica fume the increase was 11%. By combining two additions, 2% nanosilica + 10% silica fume, the increase was 48%, evidencing the existence of a synergistic effect between the additions. Regarding tensile strength by diametrical compression (Figure 4), results indicated that additions use did not induce significant improvements, especially when considering the standard deviations. However, Ganesh et al. (2016) observed gains of 17% and 24% in 28-day tensile strength of concrete, incorporating 1% and 2% nanosilica solution, respectively. It should be emphasized that the nanosilica used in this work is dispersed in superplasticizer and it makes the study of its incorporating at higher levels difficult, including the recommended levels. Moreover, the real content of silica present in material is not known, making it impossible to determine its percentage in relation to ...
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... The water:cement (w/c) factor also showed a large difference of 0.25-0.65 [10,17], which is related to the content of plasticizer [5,21,22]. In various studies, nS powder is typically mixed with plasticizer additives [5,10,17,[21][22][23], whereas others use a premixed product in colloidal dispersions known as stabilized nanosilica [24][25][26]. ...
... In addition, no more than 50% must be retained between two consecutive sieves [31], which was also observed, and no more than 25% must be retained between the N°50 and 100 sieves [31], yielding approximately 22.6%. Furthermore, the fine material was passed through the N°200 (0.075 mm) sieve should not exceeded 3% [24], which was 1.9%. ...
In recent years, nanotechnology has been applied to building materials, such as cementitious composites (e.g., mortar and concrete), to improve their properties. The aim of this study was to analyze the thermal, physical, and mechanical properties of mortars with and without silicon-dioxide (SiO2) nanoparticles. Experiments such as thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), fresh density, incorporated-air content, bulk density, capillary absorption, capillarity coefficient, flexural tensile strength, and compressive strength on prismatic specimens were performed on mortars and analyzed for different levels of nanosilica (nS). These levels were 1% and 3%, in addition to the reference mortar (0% nS). The TG-DTA curves showed an elevated content of chemically combined water and a lower content of calcium hydroxide (Ca(OH)2) in the 3% nS compositions, while the XRD curves presented a lower content of calcite and portlandite in the same mortar. These results indicate the fixation capacity of lime for the formation of calcium silicate hydrate (C-S-H), which is the primary cause of resistance in cementitious mortars. In addition, it was found that the use of nanosilica contributed to a fresh density increase of approximately 15%, which caused a minimum air-incorporated content decrease of 37% and a minimum bulk density increase of 10%. Higher densities resulted in a minimum water absorption reduction of 36%, owing to fewer pores in the mortars. Therefore, the capillarity coefficient decreased by a minimum of 41%. These nanoparticles also improved the minimum flexural tensile and compressive strengths by 88% and 158%, respectively, when using a 3% nS composition. These results can enable the use of lightweight aggregates in cementitious composites, improving their physical and mechanical characteristics and allowing greater reuse of these materials, including construction waste.
p class="Normal1"> Atualmente, no Brasil, a maioria das edificações depende do alto consumo de energia elétrica, consequência de, muitas vezes, desconsiderar estratégias para o desempenho térmico e para a eficiência energética do ambiente construído. Várias pesquisas estão sendo realizadas para estudar a viabilidade da incorporação de adições ao concreto, visando materiais com condutividade térmica que proporcione melhor desempenho térmico. Uma destas adições é a nanosílica, já muito estudada em relação à durabilidade e à resistência à compressão de concretos, porém pouco explorada quanto à condutividade térmica. Assim, neste trabalho, estudou-se o efeito da nanosílica coloidal na condutividade térmica de concretos com a incorporação de 0%, 5% e 10% em substituição em massa ao cimento. Foram avaliadas: massa específica, absorção de água, índice de vazios, resistência à compressão e condutividade térmica dos concretos desenvolvidos. Os resultados indicam que a adição de nanosílica provoca um aumento significativo na massa específica dos concretos, assim como nos valores de resistência à compressão para as amostras com 10% de nanosílica coloidal nas primeiras idades. Em relação à condutividade térmica dos concretos estudados, não foram observadas variações significativas em seus valores (variações de 0,02 a 0,22 W/mK), comparando-se os concretos com e sem adição de nanosílica coloidal. </p
