Fire resistance and mechanical properties of carbon nanotubes – clay bricks wastes (Homra) composites cement

• Effect of carbon nanotubes (CNTs) on the fire resistance of Homra/OPC blends.
• Small additions of CNTs to OPC–Homra blends improve the fire resistance.
• 0.1% CNT could be considered as the optimum addition to each mix.
• Presence of CNTs does not affect the hydration reaction of OPC or Homra/OPC blends.
• Presence of CNTs does not affect the microstructure of the formed hydrates.

This paper aims to evaluate the effect of carbon nanotubes (CNTs) on the mechanical properties and the fire resistance of Homra/OPC blends; Homra represents the solid waste generated from clay bricks industry in Egypt. The nanocomposites, thus produced, were obtained by different additions of CNTs of 0.02, 0.05, 0.1 and 0.2 mass% to Homra/OPC blends, prepared by the partial replacement of OPC by 10, 20 and 30 mass% by Homra. Fire resistance of the nanocomposite blends was studied by firing of the various blended cement pastes at 300, 600, and 800 °C for 3 h. The compressive strength values were determined for different blended cement–CNTs composites at each firing temperature, in addition, the phase composition, thermal analysis and microstructure were investigated for some selected samples. The results obtained revealed that addition of 0.1 (mass%) of CNTs showed better improvements in the thermal and mechanical properties of the hardened Homra/OPC blended cement–CNTs composites. XRD, DSC and SEM results revealed that the presence of CNTs does not affect the rate of hydration reaction of the neat OPC or Homra/OPC blends; but increases their compressive strength and fire resistance through their physical contribution; where it can further fill in the pores between the hydration products and acts as bridges between hydrates and across cracks.