Based on the slag extruded precast pile technology and active MgO-CO carbonation curing method

the feasibility of using MgO instead of cement as curing agent was studied. Effects of the pre-carbonation duration on the particle gradation

mass and moisture content

and the unconfined compressive strength of MgO-cured compacted soil were investigated by combining the X-ray diffraction (XRD)

thermo-gravimetric analysis (TGA)

mercury intrusion porosimetry (MIP)

and scanning electron microscopy (SEM) tests. The products of carbonization process and microstructure evolution characteristics were analyzed

and the mechanism of the influence of pre-carbonation duration on the strength of MgO-cured compacted soil was revealed. In pre-carbonation duration of 1−5 h

the mass of compacted soil increases rapidly and then tends to slow down with the carbonization time

but the water content shows in the opposite trend. The coefficient of uniformity C and the compactability increase with the rising number of particles in size of 1−10 m. The unconfined compressive strength increases rapidly then slows down to be stabilized. During the carbonization process

the carbonization products generated by the carbonation process are wrapped around the soil particle surface to improve the hardness. Morever

the carbonization products fill the large to super larger pores (4−40 m) in soil during the compaction

and MgO continues to hydrate and carbonize during the maintenance stage to further fill soil pores

leading to improve the degree of densification. The three mechanisms described above act synergistically to enhance the macroscopic strength of the cured compacted soil. However

with longer pre-carbonation durations

the formation of a passivating layer inhibits further carbonation. In addition

the initial low water content limits MgO hydration

reducing carbonation during the carbonation stage. These factors lead to a transition from rapid to slower strength development in the cured compacted soil.