HYDRATION OF BELITE CEMENT PREPARED FROM RECYCLED CONCRETE RESIDUES

• Published in: Ceramics (Praha) Vol. 51; no. 1; pp. 45 - 51
• Main Author: Fridrichova, M
• Format: Journal Article
• Language: English
• Published: 01.01.2007
• ISSN: 0862-5468

Undersize fractions occurring during the recycling of concrete waste were used to prepare belite clinker. The ratio of the undersizes to limestone containing a high percentage of CaO was 1 to 2.25. The mix was converted into belite cement and its hydration properties and those of two types of alite cements prepared from the same recycled undersizes were investigated. The hydration of Portland cements was a first order reaction and its progress was assessed from the content of unhydrated CaO in the cement body. Data characterising the hydration products were obtained by thermal analysis after standard reaction soaks of 1, 3, 7 and 28 days. The original CaO content (55%) in belite cement dropped to 51% after 7 days; there was only 44% of unhydrated CaO after a month. The original CaO content (56%) in ternary alite cement dropped to 21% after hydration lasting a month. The original CaO content (54%) in binary alite cement followed a similar pattern in the first 7 days, with an inflection occurring within a month and a decrease to the final value of 12% of unhydrated CaO. The velocity constants in the kinetic first order reaction were expressed statistically from the values of the residual CaO remaining after hydration and showed that belite cement prepared from recycled concrete would require an unacceptably long hydration time. 13 refs.