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This works aims to study the effect of partial substitution of ordinary Portland cement (OPC) by silica fume (SF) and fly ash (FA) on the physico-mechanical properties of the hardened OPC-FA-SF composite cement pastes. The OPC was partially replaced by 20% and 30% fly ash along with 5% and 10% silica fume. The phase composition of the hydration products was investigated using XRD and DTA techniques. It was found that, the increase of FA content in OPC-FA-SF composite cement decreases the water consistency values and increases the setting times. On the other hand, the increase of SF content leads to increase the water of consistency and decrease the setting times. The partial substitution of OPC by FA and SF leads to higher porosity values with a consequent decrease in the compressive strength values especially during the early ages of hydration. At the later ages of hydration, however, the OPC-FA-SF cement pastes possess total porosity and compressive strength values close to those of the neat OPC paste. The lower of free lime contents were obtained for OPC-FA-SF composite cement pastes with the formation of further additional amounts of CSH as a result of the pozzolanic reaction. The results showed also that, the physico-mechanical properties of composite cement paste [OPC (65%)-FA (30%)-SF (5%)] were improved at later ages. ª 2014 Production and hosting by Elsevier B.V. on behalf of Housing and Building National Research Center.

Nanotechnology helps in producing materials with prospective properties, for each field of science (physics, chemistry, bio-science as well as construction materials). Nanoparticles belong to the materials in the field of civil engineering which have a high surface area to provide high chemical reactivity. Some researchers have employed nanoparticles into cementitious materials based on ordinary Portland cement to modify the properties of this system. They have important advantages for the hydration and microstructure of cement paste to increase the rate of hydration and the amount of formed CSH gel. The aim of this work is to investigate the influence of NF on the fire resistance of OPC pastes. The NF was synthesized by thermal decomposition of basic ferric acetate fired at 275, 600 and 800°C. The crystal size of the prepared NF as previously determined was 14.6, 16.98 and 18.68 nm, respectively. OPC admixed with 1 wt% NF prepared at 275°C gives the higher fire resistance than those admixed with 2 or 3 wt%. It shows the higher bulk density, compressive strength and lower porosity up to 450°C than the blank OPC. As the firing temperature of NF increases the fire resistance diminishes. ª 2014 Production and hosting by Elsevier B.V. on behalf of Housing and Building National ResearchCenter.

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