RESUMO
Understanding of the chemistry of the Ca[OH]2-SiO2 hydrothermal reaction put the bases of the manufacture of sand-lime brick and autoclaved building materials. The effect of partial or complete substitution of Ca [OH]2 with cement dust on the lime-silica hydrothermal reaction was investigated. The pressed samples were prepared by using Ca [OH]2; silica ratio of 10: 90 by wt in which 20, 40, 60, 80 and 100% Ca [OH]2 was substituted by cement dust. The hydrothermal conditions were 10 bar [180 degree] and different periods from 4-24 hour. Major attention focused on the kinetic of the reactions, while other properties such as strength, density and porosity were also studied. The extent of hydration as measured by the chemically combined water, free lime and reacted silica, is enhanced due to the cement dust substitution. The reaction products as characterized by x-ray diffraction analysis and scanning electron microscopy [SEM] are CSH [1] and 11 A tobermorite. The results indicate that the substitution of Ca [OH]2 with cement dust accelerate the tobermorite formation and improve its crystallinity. For industry the results revealed that the substitution of lime with cement dust [by-product of cement industry] up to 50% can be used to prepare sand- lime brick with higher strength and lower cost