A novel humidity regulating material hydrothermally synthetized from concrete waste

To promote the recycling of construction wastes, a low temperature (≤ 200 ℃) hydrothermal technology for solidifying construction (concrete) waste into a tough and humidity self-regulating material has been developed, in which more than 60% of concrete waste could be recycled. During the process, the whole concrete waste including aggregates could be converted hydrothermally into tobermorite or C–S–H. The formed tobermorite could not only enhance the strength but also improve the porosity and thus enhance the humidity regulating capability. The maximum flexural strength reached up to 22 MPa, and the increased porosity could provide a good moisture adsorption/desorption performance (170 g/m 2 ). With the addition of sepiolite, the performance could be further improved (250 g/m 2 ) due to the coexistence of the formed tobermorite and remained sepiolite. The materials also exerted a remarkable damping effect on relative humidity (RH) variation indoors, e.g., the RH variation even could be decreased to 1/3 compared to that of empty reference (no humidity regulating materials were used). Graphic abstract