Comparison of various cement pastes with SCM at different ages: phase assemblage evolutions
Résumé
For economical and ecological reasons, supplementary cementitious materials (SCM) are increasingly used in concrete. Although having a lot of advantages, these concretes have different cement matrices and do not have the same evolution as a function of time as CEM I concretes.
In this paper, the microstructure of various cement pastes with/without SCM (slag, fly ash and metakaolin), has been investigated as a function of the curing time (28, 91 and 365 days). The microstructure was characterized not only by usual techniques such as XRD and TGA-DTA, but also by 29Si and 27Al NMR spectroscopy. The use of a combination of techniques for microstructural characterization allows to quantify the proportion of each cementitious phase. This quantification shows the evolution of the cementitious matrix as a function of the binder content and of the curing time. After one year, there is higher proportion of C-S-H in SCM cement pastes but there is still large amount of anhydrous phases. On the other hand, the alumina content in the C-S-H and the average length of C-S-H chains are higher for pastes with SCM than for OPC ones. Alumina phases proportions (AFt, AFm, TAH) are higher in SCM cement paste. There is more ettringite in CEM I paste and more AFm phase in SCM cement paste.