Supplementary cementitious materials interact chemically and physically with cement, influencing the formation of hydrate compounds. Many authors have analyzed the filler and pozzolanic effect. However, few studies have explored the influence of these effects on hydration, properties in the fresh and hardened states, and durability parameters of cementitious composites separately. This study investigates the influence of the replacement of 20% of Portland cement for silica fume (SF) or a 20-µm medium diameter quartz powder (QP) on the properties of cementitious composites from the first hours of hydration to a few months of curing. The results indicate that SF is pozzolanic and that QP has no pozzolanic activity. The use of SF and QP reduces the released energy at early times to the control paste, indicating that these materials reduce the heat of hydration. The microstructure with fewer pores of SF compounds indicates that the pozzolanic reaction reduced pore size and binding capability, resulting in equivalent mechanical properties, reduced permeability and increased electrical resistance of the composites. SF and QP increase the carbonation depth of the composites. SF and QP composites are efficient in the inhibition of the alkali-aggregate reaction. The results indicate that, unlike the filler effect, the occurrence of pozzolanic reaction strongly influences electrical resistance, reducing the risk of corrosion of the reinforcement inserted in the concrete.
RESUMO Um método alternativo para produção de concretos ecoeficientes seria a substituição parcial de cimento Portland por resíduos de pastas e argamassas submetidas a um tratamento termomecânico. Neste contexto, este estudo avalia a influência da relação água/cimento (a/c) e do tamanho médio das partículas na decomposição térmica do cimento hidratado. Pastas de cimento com três relações a/c (0,40, 0,50 e 0,60) e curadas por 28 dias foram moídas para obtenção de granulometrias com tamanho médio de 0,60 mm e 0,15 mm. A decomposição térmica das pastas foi analisada por termogravimetria (TGA), difração de raios X (DRX) e espectroscopia no infravermelho por Transformada de Fourier (FTIR). A análise de TGA indica que o teor de água quimicamente combinada é favorecido pelo aumento da relação a/c entre 0,40 e 0,50, mas é constante para a/c de 0,50 e 0,60. A redução do tamanho médio quase não interfere nas curvas de TGA. De acordo com as análises por DRX e TGA, a maior parte dos hidratos se decompõe até 500-550°C, enquanto que silicatos de cálcio e aluminatos de cálcio similares às fases anidras do cimento Portland foram detectados na pasta aquecida a 750°C. Assim, temperaturas mais altas seriam necessárias para a completa recuperação do cimento anidro em pastas hidratadas.
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