GAS TRANSPORT PARAMETERS OF RECYCLED CONCRETE AND CLAY BRICK AGGREGATE BLENDED WITH AUTOCLAVED AERATED CONCRETE GRAINS

Gas diffusivity (D-p/D-0: the ratio of gas diffusion coefficient, D-p, to gas diffusion in free air, D-0) and air permeability (k(a)), and their variations with air-filled porosity (epsilon) play key roles in surface gas exchange and vapor transport in permeable pavement and water-retentive pavement systems. This study carried out a series of laboratory measurements of D-p/D-0 and k(a) for graded recycled concrete (RC) and clay brick (RCB) aggregates, and RC and RCB blended with autoclaved aerated concrete (AAC) grains at proportions of 20% and 40%. The tested samples were saturated after compaction, and the D-p/D-0 and k(a) were measured during the drying process from saturation to air-dry. Results showed that D-p/D-0 and k(a) of graded RC and RCB decreased most with increased proportions of AAC grains; in particular, the effect of AAC blending on D-p/D-0(epsilon) relationships decreased. For most tested samples, pore-connectivity factor and diffusion-based tortuosity (T) gradually increased with drying, and T values were decreased slightly by blending with AAC grains. Equivalent pore diameter for gas flow values of graded RC and RCB showed a clear decrease with drying; on the other hand, those of AAC blended RC and RCB did not depend on epsilon. Combining previous models and fitted T(epsilon) relations for tested samples, the D-p/D-0(epsilon) relations and MLWs for k(a)(epsilon) captured well the values of graded RC and RCB blended with AAC grains, implying that the previous gas transport parameter models would be useful for quick assessment of roadbed materials.