Concrete thermal and optical property sensitivities to mixture proportions

The thermal (thermal conductivity, heat capacity, and thermal diffusivity) and optical (albedo and emissivity) properties of concrete determine its temperature, which has important applications in pavement design, mass concreting, and Urban Heat Islands. For a given set of constituent materials, these properties depend on the concrete mixture proportions. To study this dependence, a rotatable central composite experimental design was developed, which accounts for linear, quadratic, and interaction relationships between dependent and independent variables. Four mix proportions were used as predictive variables: the volume fraction of paste (VP), the volumetric ratio of fine to coarse aggregates (F/C), fly ash to cementitious materials ratio (FA/CM), and water to cementitious materials ratio (W/CM). Based on the experimental design, 25 samples were cast and their thermal and optical properties measured. The R2 for the relationships obtained from the model ranged from 0.44 to 0.79, with the error being generally less than 10%. All the properties were sensitive to VP, and most were also sensitive to FA/CM and W/CM ratios. Most of the properties also showed sensitivity to the interaction between a subset of the mix proportions, in addition to the direct linear relationships.