الفهرس 
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Abstract
This work focuses on using the pozzolanic materials such as silica fume and fly ash in producing pozzolanic and composite cements. The use of these cements has attracted considerable interest from both scientific and technological points of view, since the beginning of this century. The aim of the present study is to investigate the pozzolanic activity of fly ash with lime and the hydration characteristics of different silica fume-pozzolanic cement pastes as well as the silica fume-fly ash composite cement pastes. The investigation of the hydration characteristic of pozzolanic or composite cement pastes assessed by the determination of combined water and insoluble residue contents, total porosity, bulk density, compressive strength for the cement pastes up to 90 days. IR-spectroscopy and DTA technique were used. The resistance of the pozzolanic or composite cement pastes against firing was also investigated by the determination of the ignition loss, bulk density, total porosity, compressive strength of the cement pastes treated up to 800oC, visual inspection as well as by XRD techniques for some selected samples. The addition of 5-10% silica fume to Portland cement increases the W/C ratio, shortened setting times, decreases the total porosity and gives reasonable compressive strength. The substitution of silica fume by fly ash shortened setting time and decreases the total porosity, increases bulk density and enhances the compressive strength of the composite cement pastes. Also, fly ash has a slow pozzolanic activity at early ages. On the other side, it can be concluded that pozzolanic cement containing silica fume greatly enhances the thermal stability of OPC paste up to 600oC. Also, the composite cement pastes made from 15-10% SF + 5-10% FA can be used as fire resistance cement up to 800oC.