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Roadbed materials of base and subbase layers are frequently unsaturated caused by rainfall, drainage, and evaporation. However, the movement of water in these layers is still poorly understood because of lacking data on unsaturated properties such as the water retention curve (WRC) and unsaturated hydraulic conductivity ( K ). This study, therefore, recycled concrete aggregates (RCA) blended with autoclaved aerated concrete (AAC) grains (% of substitution on the mass basis from 0 to 50%) were used to examine the WRC and K for unbound roadbed materials in Vietnam using the evaporation method. Natural aggregates (NA) and Toyoura sand were used as control and reference material. Results showed that compared to NA100% and RCA100%, the water capacity of RCA mixed samples was much improved by blending AAC grains. Toyoura sand showed higher water capacity at saturation compared to RCA100% and NA100%, but quickly became lowest when matric potential exceeds 10 kPa. Toyoura sand showed the highest saturated hydraulic conductivity, but decreased dramatically around 10 kPa, while other tested samples remained higher K . The original van Genuchten – Mualem model was well fitted for Toyoura sand and underestimated for other tested samples, but showed an agreement with estimated conductivity parameter ranging from – 3.0 to -4.4.
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