Abstract Carbonate sands (CS) have the potential to be utilized as construction materials, and their porous particles may bring unique thermal properties, which is critical for the thermal design of geosystems; however, this area of research is highly understudied. The present work provides a new contribution in this field by investigating the thermal conductivity (λ) of five uniform fractions of CS from the South China Sea, with emphasis on the influence of particle size and relative density of the sand. The impact of the size of particles on the index void ratios and thermal conductivity of the samples was profoundly different from that of silica sands. Contrary to silica sands, the extreme void ratio (emax, emin), which is critical for calculation of relative density, of the CS increased as the mean grain size increased. The maximum thermal conductivity of each fraction was negatively correlated with the particle size, and the thermal conductivity of the finer fractions exhibited higher sensitivity to the packing density. Literature models were found to be ineffective in predicting the thermal conductivity of the CS given the unique thermal energy transferring mechanisms of the porous particles. Two thermal conductivity models, stemming from semi-analytical and empirical approaches, were proposed in the light of providing useful guidance for the thermal designs that include CS.
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