Reactivity of low-temperature belite and the strength of its paste

Title: Reactivity of low-temperature belite and the strength of its paste
Author(s): W. Kurdowski
Paper category : conference
Book title: International RILEM Symposium on Concrete Science and Engineering: A Tribute to Arnon Bentur
Editor(s): K. Kovler, J. Marchand, S. Mindess and J. Weiss
Print-ISBN: 2-912143-46-2
e-ISBN: 2912143586
Publisher: RILEM Publications SARL
Publication year: 2004
Pages: 129 - 136
Total Pages: 8
Nb references: 10
Language: English

Abstract: A substitution of a major part of alite by belite and the production of belite cements has attracted the interest of specialists for a long time. However, a very slow rate of hydration and much lower strength up to 90 days, is the main disadvantage of belite.
The properties of belite synthesized at low temperature from C-S-H as a raw material, were investigated. This belite has a very high specific surface, but very different properties depending on the C-S-H heat treatment and burning temperature. The influences of some admixtures were also tested. Burning of the C-S-H phase in the temperature range from 700 to 1000°C yielded X-ray pure (bêta) phase. The specific surface as well as the hydraulic activity of belite decreased with increasing burning temperature. This belite reacts quickly with water giving one sharp exothermic peak on the calorimetric curve. Also, the liquid phase quickly became oversaturated by calcium hydroxide. These results seem to indicate that the reaction takes place mainly as a topochemical process.
The strength of the paste was very different. For the case of non-autoclaved C-S-H, the best results were obtained from the sample burned with the addition of sodium sulphate; for autoclaved samples belite burned with sodium silicate produced the best results. However, the strength of all samples was relatively low. Relatively good strength was obtained from the sample of belite paste after autoclaving at saturated steam pressure for 4 hours at 200°C. In this sample, part of the C-S-H was replaced by (alpha)C2S hydrate.
Very reactive belite cements can be produced from plastic raw materials such as chalk and marl with high silica modulus. These cements can consist of about 50% belite and 30% alite and give high strength mortars.

Online publication: 2004-02-04
Publication type : full_text
Public price (Euros): 0.00
doi: 10.1617/2912143586.012