Effect of Nanosilica Additions on Belite Cement Pastes Held in Sulfate Solutions (original) (raw)
2007, Journal of the American Ceramic Society
Fly Ash Belite cement (FABC) pastes with and without nanosilica additions have been prepared and maintained in sulfate solutions (Na 2 SO 4 0.5 M) for 180 days. The mechanical performance and the changes in microstructure have been monitored at 28, 90 and 180 days by compressive strength, X-ray diffraction (XRD) and 29 Si MAS NMR measurements. We have found that, unexpectedly, and contrary to what happens in Ordinary Portland Cements (OPC), the addition of nanosilica particles induces an initial fall in the compressive strength of the samples. Only in samples maintained for long time (180 days), do the nanosilica addition improve the mechanical properties. Our XRD and 29 Si NMR experiments have revealed that although the nanosilica additions trigger the consumption of Belite phases, this is not always accompanied by formation of longer Calcium-Silicate-Hydrate (C-S-H) gel