Mechanical performances and microstructural characteristics of reactive MgO-carbonated silt subjected to freezing-thawing cycles

The characteristics of reactive magnesia (MgO)-carbonated silt in respect to long-term stability have not been well understood in severely cold climate despite the usage of reactive MgO in enhancing the engineering performances. Under the binder content of 15% and initial water content of 25%, MgO-admixed silt specimens were carbonized for 3 h and 6 h and then subjected to different numbers of freezing-thawing (F-T) cycles. After different F-T cycles, the physico-mechanical properties of MgO- carbonated silt were analyzed in comparison with Portland cement (PC)-stabilized silt through physical and unconfined compression tests. Besides, a series of micro tests on MgO-carbonated specimens was performed including X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests. The results demonstrate that both mass change ratio and moisture content of carbonated/stabilized silt decrease, and these values of MgO-carbonated silt are significantly lower while the density is higher compared to PC-stabilized silt. The strengths and moduli of MgO-carbonated silt are still two times higher than those of PC-stabilized specimens and the strength change ratio of keeps above 0.8 after F-T cycles. There is no visible transformation between nesquehonite and dypingite/hydro-magnesite, although the XRD peaks of nesquehonite decrease and the bonding and filling effects weaken slightly. After 6 and 10 F-T cycles, the pore-size characteristics changed from a unimodal distribution to a three-peak and bimodal distribution, respectively. The total, macro and large pore volumes increase obviously while the medium and small pore volumes decrease except for intra-aggregate pore. The findings show better F-T durability of MgO-carbonated silt, which would be helpful for facilitating the application of MgO carbonation in the soil treatment. (C) 2021 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V.