Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) have been used to study the microstructural changes and phase development that take place during the hydration of cubic (pure) and orthorhombic (Na-doped) tricalcium aluminate (C3A) and gypsum in the absence and presence of lime. The results demonstrate that important differences occur in the hydration of each C3A polymorph and gypsum when no lime is added; orthorhombic C3A reacts faster with gypsum than the cubic phase, forming longer ettringite needles; however, the presence of lime slows down the formation of ettringite in the orthorhombic sample. Additional rheometric tests showed the possible effects on the setting time in these cementitious mixes.
Kirchheim AP, Fernàndez-Altable V, Monteiro PJM, Dal Molin DCC, Casanova I (2009) Analysis of cubic and orthorhombic C3A hydration in presence of gypsum and lime. Journal of Materials Science 44: 2038–2045. Available: http://dx.doi.org/10.1007/s10853-009-3292-3.
The authors acknowledge the financial support of CAPES (Fundacao Coordenacao de Aperfeic, oamento de Pessoal de Nivel Superior - Ministerio da Educacao - Brasil) and CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico Ministerio da Ciencia e Tecnologia - Brasil). Also we are grateful to the staff of Electron Microscope Laboratory at University of California, Berkeley for helping in the acquisition of the images, and Oscar Reyes, from Technical University of Catalonia (UPC) on the rheological measurements. The research was supported by the National Science Foundation (grant CMS- 981275) and KAUST.