[A-GE29] Energy-Environment-Water Nexus and Sustainable Development

[AGE29-02] Thermal conductivity of recycled concrete aggregates blended with autoclaved aerated concrete grains

*Van Nam Pham¹、Akihiro Matsuno¹、Kengo Nakamura¹、Ken Kawamoto¹ (1.Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama City, Saitama Prefecture 338-8570, Japan)

キーワード：Thermal conductivity, Archie`s law, Water retention curves, Recycled concrete aggregates, Autoclaved aerated concrete

Whether permeable pavement systems (PPS) have the potential to mitigate urban heat island (UHI) effect remains controversial. The variety of materials used and different design techniques can lead to different observations when assessing the effectiveness of PPS in mitigating the UHI. Thermal properties such as thermal conductivity and heat capacity of roadbed materials are crucial for understanding heat transport in pavements. Archie`s second law has been employed to describe thermal conductivity at fluid-unsaturated conditions of sand and soil for uni-modal porous media, but its applicability for materials with bi-modal porous media is somewhat limited. In this study, recycled concrete aggregates (RCA) from construction and demolition waste blended with autoclaved aerated concrete (AAC) grains made from AAC scraps [with a % of substitution on a mass basis from 0 to 50%) were used to examine the water retention curves [WRC, water potential (-cm H<sub>2</sub>O) vs. volumetric water content (cm<sup>3</sup>/cm<sup>3</sup>)] and thermal conductivity for unbound roadbed materials. Natural aggregates (NA) were used as a control material. The WRC was measured using a drying process using a combinational method with a hanging water method at water potential < 100 cm H<sub>2</sub>O, a pressure plate method at water potential greater or equal to 100 cm H<sub>2</sub>O, and a dewpoint potentiometer at water potential at near 10<sup>6</sup> cm H<sub>2</sub>0. At each corresponding water potential, two thermal conductivity meters (KD2-Pro; Decagon Devices, Pullman, WA, USA and QTM-700; Kyoto Electronics Manufacturing Co., Ltd., Japan) were used to measure thermal conductivity values. Archies`s second law was used to test normalized thermal conductivity considering a suggested percolation threshold at air-dried condition (i.e., at residual volumetric water content ), while the uni- or bi-modal van Genuchten (vG) was used to fit the measured water retention data. The results showed that the relationship between normalized thermal conductivity and volumetric water content of NA can be well described using a convex curve (i.e., the saturation exponent, n_a>1). However, for RCA and RCA blended samples, the curves are concave (n_a<1), suggesting that the Archie`s second law does not adequately capture the thermal conductivity of these materials. Furthermore, a prediction curve derived from modified Archies`s second law and vG model well captured the measured thermal conductivity, providing a promising tool to predict thermal conductivity in which only data on water potential is available.