Addition of fine materials, as clay bricks or Homra (H) to Ordinary Portland cement (OPC) is evidently increases resistance to firing. Effect of firing temperature on physical, mechanical properties and phase composition of cement pastes is investigated. H can react with lime liberated from hydration of OPC. This improves morphology and microstructure of formed hydration products. OPC cement was partially substituted by 0, 5, 15, 25 and 35 wt.% H. Cement pastes were subjected to firing for 3 hours at temperatures 100, 200, 300 400, 500 and 600°C. Results showed that loss on ignition of various cement pastes increased with temperature as well as with H. Density decreased with temperature up to 400°C, while porosity increased, Above 400°C, density increased and porosity decreased. Compressive strength of OPC pastes increased with temperature up to 500°C and then decreased. Those incorporated H increased only up to 400°C and then decreased. Hardened cement pastes with 15% H recorded highest compressive strength value at 400°C while the OPC at 500°C. SEM images showed a microstructure of well-developed crystals of CSH and CAH. Ca(OH)sub2/sub are spreading in matrix at temperatures up to 400°C. There are some cracks at 600°C.
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