Durability of the bio-carbonated reactive MgO cemented construction and demolition waste: Effect of wetting-drying cycles

Bio-carbonation of reactive MgO has been regarded as a promising and eco-friendly method for construction and demolition waste (CDW) cementation in various geotechnical engineering applications. However, the beneficial effect of bio-carbonation of reactive MgO cemented CDW (BCM-samples) can be altered when exposed to wetting-drying cycles induced by extreme climate changes or groundwater fluctuations. To better understand the durability of BCM-samples and their underlying deterioration mechanisms, a series of BCM-samples was prepared to investigate their physical-mechanical performance and microstructure evolution subjected to the wetting-drying cycles. The results indicated that the wetting-drying cycles can deteriorate the BCM-samples, and their physical-mechanical behaviors change quickly at the cycle beginning and then smoothly after 2 cycles. With the increase in cycling, the apparent deterioration with efflorescence and microcrack development can be observed. The mass loss and water absorption rates increased while the dry density, compressional wave velocity, and unconfined compression strength decreased. Urea pre-hydrolysis treatment can significantly improve the durability of BCM-samples, as the more hydrated magnesia carbonates (HMCs) enhance the cementing effects. After 10 cycles, the UCS of pre-hydrolyzed samples decreased 25.4% to 4.45 MPa, while that of ordinary samples decreased 50.7% to 1.20 MPa. The deterioration of BCM-samples caused by wetting-drying cycles can be attributed to two factors. One of the main factors is the structural integrity changes caused by the rapid loss of soluble material at the initial cycling stages. Another factor is the decrease in cementation induced by the loss of brucite and HMCs at the following cycle stages.