[A-GE31] Energy-Environment-Water Nexus and Sustainable Development

[AGE31-P04] Gas transport parameters of recycled concrete aggregates with different fines content and initial compaction water content

*Hong Nam Thai^1,2, Ken Kawamoto^1,2 (1.Saitama University, 2.Hanoi University of Civil Engineering)

Keywords:recycled concrete aggregates, fines content, water content, gas diffusivity, air permeability

Nowadays, water-retentive pavement and permeable pavement systems have been applied widely to reduce the effects of urban heat islands and flooding. Gas transport parameters including gas diffusivity (D_p/D₀) and air permeability (k_a) play important roles not only in the exchange of gas between the surface and the atmosphere but also in the movement of water vapor in the pavement layers. It is well known that gas transport parameters depend significantly on the air-filled porosity (e) of soils. Fines content (F_c, < 0.075 mm) and initial compaction water content (w) are the main factors that affect the compaction degree, thereby affecting the porosity and pore structure of the specimen. However, until now the effects of F_c and w on the gas transport parameters have not been fully understood. This study carried out a series of laboratory tests to measure D_p/D₀ and k_a of unbound road base materials using recycled concrete aggregate with nominal maximum particle size D_max = 37.5 mm, and two different F_c of 5% and 20%. After the compaction with modified proctor method at different w [i.e., air dry (w_AD), “bulking” (w_bulking), and optimum water contents (w_opt)], specimens were saturated, then the water content was reduced by stepwise drainage at different water potential energies (|ψ|). At each |ψ| value, D_p/D₀ and k_a of the specimens were measured by a diffusion chamber method and a constant air head method, respectively. The results showed that at the same value of |ψ|, D_p/D₀ and k_a of the specimens with higher F_c value were usually lower than those of the specimens with lower F_c value. The pore connectivity factor of most tested specimens increased, while the diffusion-based tortuosity decreased with the increase of e. Equivalent pore diameters for gas flow (d_eq) values of the lower F_c specimens were remarkably higher than those of the higher F_c specimens. In addition, d_eq values of all specimens with F_c of 20% stabilized with the change of e and ranged from 1.5 to 2.5 μm, whereas d_eq values of specimens with F_c of 5% increased with the increase of e until e around 0.12 and became constant when e > 0.12 (d_eq around 20 μm for specimens compacted at w_AD and w_opt, d_eq around 100 μm for specimen compacted at w_bulking).