The mineralogy and microstructure of three composite cements with high replacement levels

The hydration products of three high replacement, composite cement pastes, i.e. Portland cement mixed with 75% and 90% ground, granulated blast furnace slag (BFS) and 75% pulverised fuel ash (PFA), are reported and compared with those from a 100% ordinary Portland cement (OPC) paste. The samples were cured in air under the same temperature and humidity conditions and tested at various times for up to six months. The hydration products were identified by means of X-ray diffraction (XRD) and their microstructure by scanning electron microscopy (SEM). Although the observed hydration products were mostly as expected., due to the high replacement levels, the degree to which these phases was present was unusual. In particular the calcium hydroxide initially formed in the BFS-cement systems was totally consumed within six months, indicating the important pozzolanic behaviour of BFS at such high replacement levels. (C) 2002 Elsevier Science Ltd. All rights reserved.