Diffusive and convective transport properties and pore-network characteristics of recycled, compacted concrete aggregates for use as road pavement materials

Gas transport parameters, such as gas diffusivity (D_p/D₀) and air permeability (k_a) of materials, and pore-network properties play important roles in the movement of gases and water vapor in road pavement layers and contribute to assessment of the urban heat island effect in urban areas. This study carried out a series of laboratory tests to measure the D_p/D₀ and k_a of recycled concrete aggregates (RCA) used for road base and subbase materials at variable fines contents and moisture conditions. The results revealed bimodal patterns in both water retention and the derived pore-size distribution curves for tested RCA samples. Both fines and initial moisture contents under compaction affected the characteristics of pore networks and structures, such as the effective pore space and water blockage effects that control the gas transport parameters of porous media in RCA samples. Especially, the increase of fines significantly reduced the pore-network parameters. The structure-dependent water-induced linear reduction (SWLR) model functioned well to predict the D_p/D₀ of RCA samples when the air-filled porosity was less than 0.175 cm³ cm⁻³. The most likely windows for k_a of RCA samples were predicted by equations developed from the SWLR model.