Fractal modeling on the effective thermal conductivity of aerogels incorporated cementitious composites (AICC) incorporating the ITZ effects

Recent research has increasingly focused on the application of aerogels in cementitious composites, given their exceptional thermal insulation properties despite their relatively low mechanical strength. Aerogels incorporated cementitious composites (AICC) presents a potential solution for achieving a balance between superior thermal insulation and enhanced mechanical performance. This study proposes a prediction model based on the configuration of the three-phase Sierpinski carpet model for the effective thermal conductivity of AICC by innovatively incorporating the interfacial transition zone (ITZ) effect. A parametric analysis was systematically conducted and the results were validated against experimental data for aerogel incorporated ultra high-performance concrete (AIUHPC), mortar (AIM) and paste (AIP). The selection of either constant C or n in calculation and the effect of ITZ properties (i.e., thermal conductivity, porosity and thickness) on the predicted results were mainly discussed. The results indicate that using a constant C is more appropriate for low content of aerogels, while the algorithm by constant n demonstrates more accurate results for the higher content of aerogels (50 vol%∼). The thermal conductivity of ITZ is more significantly affected by the disparity in thermal conductivity between the matrix and the aerogels than by the aerogel size. The impact of aerogels addition on the fractal dimension of AICC is more pronounced at aerogel content higher than 40 vol%. By explicitly considering the influence of ITZ, the enhanced ITZ-incorporated tri-phase carpet model achieves ≤10 % prediction error for AICC thermal conductivity, highlighting the critical role of interfacial effects in the composite.