Bio-carbonation of reactive magnesia cement (RMC), an innovative and potentially sustainable cementing technology, has been proposed as a promising strategy to stabilize the construction and demolition wastes (CDW) for underwater engineering. A series of underwater bio-carbonation experiments on CDW samples with various RMC content and bacteria concentration were conducted to verify the feasibility of the method. Experimental results showed that bio-carbonation of RMC had the ability to stabilize CDW subjected to the underwater environment. The unconfined compressive strength (UCS) of the bio-carbonized CDW samples was up to 1006.04?kPa with 12% of RMC content, which was 11.2 times of samples stabilized by RMC hydration only. The stabilization effect was facilitated by the increase of the RMC content and bacteria concentration. The UCS of the sample with 12% of RMC content was 10.64 times as much as that of the sample with 4% of RMC content. The UCS of the sample stabilized with concentrated bacteria solution was increased by 218.19%. The high RMC content and bacteria concentration also changed the sample failure characteristics from ductileness to brittleness. Based on the measurements of the degree of carbonation (DC), urea utilization ratio (UUR), and microstructure observations, the CDW stabilization mechanism through the bio-carbonation of RMC was discussed. The increasing UCS of the bio-carbonized CDW samples can be attributed to the formation of the brucite and hydrated magnesia carbonates (HMCs) by the combined effects of hydration of RMC and the carbonation of brucite. The formed brucite and HMCs provide excellent filling, bonding, and coating effects between the CDW particles than that of brucite only. The higher RMC content and bacteria concentration promote the urea hydrolysis and RMC carbonation processes, resulting in forming more brucite and HMCs. The large amount of HMCs forms a stable spatial network structure that facilitates stabilization performance and improves the mechanical properties. The coupling effect of the high adsorption characteristic of RMC, CDW, and the fast bio-carbonation ratio makes it possible for the proposed method to be applied to underwater engineering.

» Author: Dian-Long Wang, Chao-Sheng Tang, Xiao-Hua Pan, Rui Wang, Jian-Wen Li, Zhi-Hao Dong, Bin Shi

» Publication Date: 13/06/2022

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