Influence of addition of two typical activated carbons on fertility properties and mechanical strength of vegetation concrete under freeze-thaw conditions

Under freeze-thaw conditions, the substrates used for ecological protection degrade, which involves decreases in compactness and fertiliser retention ability. As such, our purpose in this study was to use two typical types of activated carbon (AC), wood-based activated carbon (WAC) and coal-based activated carbon (CAC), to enhance the antifrost property of vegetation concrete (VC). We investigated the effects of five different proportions of planting soil weight (0.5 %, 1 %, 2 %, 4 %, and 6 %) mixed in each type of AC to determine their influence on the physical, mechanical, chemical, and biological properties of VC. The VC samples prepared without AC were used as control check (CK). The results showed that AC addition effectively enhanced the nutrient retention and microorganism capacity of VC under freeze-thaw conditions (10 and 60 freeze-thaw cycles). The leaching loss rate of ammonium nitrogen (NH4+-N) decreased to 31.98 % for WAC-6 %-60 from 46.87 % for CK-60, and the microorganism biomass carbon (MBC) increased to 138.54 mg·kg-1 for WAC-6 %-60 from 103.52 mg·kg-1 for CK-60. However, we observed some negative effects, including decreases in the cohesion and internal friction angle. In addition, the water holding capacity and matric suction first increased and then decreased as the proportion of AC mixed in the VC increased, with a turning point of approximately 2 %. By comprehensively considering previous VC eco-restoration technology study results, the recommended mixing amount of AC is 1 %-2 %, which would take full advantage of the benefits of AC and ensure that any negative effect of its use falls within an acceptable range. In addition, WAC generally performed better than CAC, but the aging rate of the former was faster than that of the latter according to scanning electron microscopy (SEM) images and dissolved organic carbon (DOC) analysis. From our results, we concluded that incorporating AC into VC improves the suitability of VC when applied in freeze-thaw conditions.