Improving the elevated temperature behaviour of foamed concrete through nano titania addition and microstructure control

This study investigates the effectiveness of nano-titania (NT) as a nano-additive for enhancing the performance and elevated-temperature resistance of foamed concrete (FC). The novelty of this research lies in the comprehensive evaluation of the residual mechanical, transport, thermal, and microstructural behaviour of NT-modified FC after exposure to temperatures of up to 800 °C. NT was incorporated at dosages of 0.5-2.0% by weight of cement, and the performance of the resulting FC was assessed in terms of fresh-state properties, shrinkage, mechanical strength, ultrasonic pulse velocity, transport behaviour, thermal properties, and microstructural characteristics. The results showed that NT reduced workability and shortened setting time, while significantly improving the overall performance of FC under both ambient and elevated-temperature conditions. Among the tested mixtures, the incorporation of 1.5% NT provided the optimum performance. At room temperature, this dosage increased the compressive strength by approximately 40% compared with the control mix. More importantly, after exposure to 800 °C, the residual compressive strength ratio increased markedly from 18% for the control FC to 57% for the FC containing 1.5% NT, indicating a substantial enhancement in thermal resistance. NT also improved the pore structure by reducing the average pore diameter from 580 to 440 µm at 20 °C and from 820 to 620 µm at 800 °C, which contributed to lower permeability and porosity, as well as improved thermal stability. Microstructural observations from SEM and MIP confirmed that NT promoted a denser and more homogeneous matrix through pore refinement and improved hydration development, leading to enhanced residual performance after high-temperature exposure. Overall, the findings demonstrate that NT is an effective nano-modifier for producing FC with superior strength, durability, and fire resistance, with 1.5% NT identified as the optimum dosage.