Hydration of a Portland cement blended with calcium carbonate Jo Dweck a,* , Pedro Mauricio Buchler b , Antonio Carlos Vieira Coelho b , Frank K. Cartledge c a Inorganic Process Department, School of Chemistry, Federal University of Rio de Janeiro, Bloco E do CT, Sala E-206, Cidade Universita Âria, 21900 Rio de Janeiro, Brazil b Chemical Engineering Department, Polithecnic School, University of Sa Äo Paulo, Sa Äo Paulo, Brazil c Chemistry Department, Louisiana State University, Baton Rouge, LA 70803, USA Received 4 August 1999; received in revised form 1 October 1999; accepted 6 October 1999 Abstract The hydration of a commercial Portland cement blended with calcium carbonate was studied by thermal analysis. TG, DTA and DTG analyses were performed on pastes prepared with a water to cement weight ratio of 0.5, after different setting times during the ®rst 28 days of hydration. The analyses were run from 288C to 10008C with a 108C/min heating rate and 100 ml/ min of air as the purge gas. All the analyses were performed after a drying step at 288C in the equipment itself, using the purge gas as the drying agent, resulting in a more effective and less time-consuming method than other conventional drying procedures. The original cement contains a partially decomposed dihydrated calcium sulfate, which is regenerated after 1 h of hydration and is consumed in about 16 h of setting. The results indicate that TG and DTG curves are faster and more precise tools than DTA curves to identify and to quantify all the main hydrated and carbonated phases which are present in the pastes, especially in the case of this cement blended with calcium carbonate, the total content of which cannot be estimated correctly by DTA as hydration proceeds. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Blended Portland cement; Hydration; Calcium carbonate; Thermal analysis 1. Introduction The solidi®cation/stabilization of hazardous wastes by cement-based binders is a technology which has been applied to many types of wastes and industrial ef¯uents, mainly those containing heavy metals. The process has the potential for effectively immobilizing hazardous constituents, but may not do so if the cement matrix is altered by the waste. Consequently, we are interested in developing con- venient and accurate tools for determining the composition of cement pastes. The present paper presents a study, by thermal analysis, of the hydra- tion of a Portland cement blended with calcium carbonate, which is being used by the authors to solidify tanning wastes. The data are being used as a reference to compare the changes in the cement Thermochimica Acta 346 (2000) 105±113 * Corresponding author. Tel.: 55-21-590-3192; fax: 55-21- 590-4991. E-mail address: dweck@h2o.eq.ufj.br (J. Dweck). 0040-6031/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII:S0040-6031(99)00369-X