[A-GE28] Energy-Environment-Water Nexus and Sustainable Development

[AGE28-P11] Measurements of unsaturated hydraulic properties for recycled concrete aggregates blended with AAC grains using an evaporation method

*Van Nam Pham¹, Quoc Cuong Nguyen¹, Akihiro Matsuno¹, Kengo Nakamura¹, Hoang Giang Nguyen², Ken Kawamoto^1,2 (1.Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama City, Saitama Prefecture 338-8570, Japan, 2.Hanoi University of Civil Engineering, 55 Giai Phong, Hai Ba Trung, Hanoi, Vietnam)

Keywords:Water retention curves, Unsaturated hydraulic conductivity, Evaporation method, Recycled concrete aggregates, Autoclaved aerated concrete

Water movement and balance in unbound roadbed materials are controlled by hydraulic properties such as water retention and saturated/unsaturated conductivities. This study measured water retention curves (WRCs) and unsaturated hydraulic conductivity of unbound roadbed materials made from recycled concrete aggregate (RCA) blended autoclaved aerated concrete (AAC) grains by using an evaporation method (HYPROP2, METER Group, Inc., USA). The tested RCA and AAC were made from construction and demolition waste and scrap in Vietnam, and graded RCA with a maximum diameter of 37.5 mm blended with AAC grains with % of substitution on the mass basis varied from 0 to 50 % (RCA100%, RCA95%+AAC5%, RCA90%+AAC10%, RCA70%+AAC30%, and RCA50%+AAC50%) were prepared in the laboratory. For the evaporation method, the tested samples were first fully saturated, and WRCs and unsaturated hydraulic conductivities were measured under the main drying process till water potential ranged from -10^-1 to close to -10³ kPa. Besides, saturated hydraulic conductivities for the tested samples were measured independently using a constant head method, and WRCs in the dry range (i.e., ≧ 10³ kPa) were estimated by using a dewpoint potentiometer (WP4C, METER Group, Inc., USA). The measured WRCs were fitted using either unimodal or bimodal VG models (van Genuchten, 1980; Durner, 1994), and measured saturated/unsaturated hydraulic conductivities were estimated based on VG-M model (Mualem, 1976). The results showed that water retention capacity increased and saturated/unsaturated conductivities decreased slightly with increasing AAC %, and the VG models well captured the measured WRCs for all tested samples. The VG-M model also estimated well the measured saturated/unsaturated conductivities for tested samples, however, the fitted pore-connectivity and/or tortuosity parameter, l, became negative values ranging from -5.8 to -4.0. This suggests strongly that the original l=0.5 (Mualem, 1976) is not applicable to estimated unsaturated hydraulic conductivities for unbound roadbed materials made from RCA and RCA blended with AAC grains.