A lab study on lean clay from Jiaxing, China shows that a magnesium oxide-metakaolin binder can replace part of Portland cement in soil stabilization while locking CO2 into the material. After 28 days of curing and three days of accelerated carbonation, unconfined compressive strength rose from 0.740 to 1.266 MPa. X-ray and microscopy work showed CO2 converted brucite into nesquehonite crystals that filled pores and bridged cracks. The mix design matters. Equal masses of MgO and metakaolin gave strong early results, and the hydration gel had to develop before carbonation added much value. The authors estimated the MgO-metakaolin route emits about 19% less CO2-equivalent than Portland cement per tonne of treated clay, although the tests used 20% CO2 in the lab, not natural exposure. The paper appears in Case Studies in Construction Materials.
