Model for the effective thermal conductivity of concrete considering the heat transfer process enhanced by carbon fibers

Thermal conductivity serves as a pivotal parameter characterising concrete's heat transfer capacity, and its reliable prediction holds significant importance for temperature control and crack prevention in concrete structures. In engineering practice, fibres are commonly incorporated to enhance the mechanical properties of concrete structures and limit crack propagation. However, as fibres constitute a heterogeneous phase with high aspect ratios and random distribution, traditional models based on the assumption of isotropy struggle to accurately predict their effective thermal conductivity. Therefore, this study employs multiphase composite theory to treat fibre-reinforced concrete as a three-phase composite comprising ‘solid-liquid-gas’ phases, aiming to establish a thermal conductivity prediction model correlated with fibre content, porosity, and saturation. Experimental testing of thermal conductivity was conducted under varying aggregate volume fractions, fibre contents, porosities, and saturations to define model parameters. Results demonstrate that the new model reliably predicts concrete thermal conductivity within reasonable ranges of fibre content, porosity, and saturation, exhibiting an error margin not exceeding ±9.27% compared to experimental data. This study provides a robust theoretical foundation for the thermal design of fibre-reinforced concrete.