Effect of CO₂ concentration on strength development and carbonation of a MgO-based binder for treating fine sediment

We previously described a MgO-based binder for treating fine sediment and simultaneously store CO₂. Here, we describe a study of the physical/mechanical characteristics and carbonation reactions of the MgO-based binder used to solidify/stabilize fine sediment in atmospheres containing different CO₂ concentrations. Carbonation of the sediment treated with the MgO-based binder at the atmospheric CO₂ concentration markedly improved the compressive strength of the product. The compressive strength was 4.78 MPa after 365 days of curing, 1.3 times higher than the compressive strength of sediment treated with portland cement. This improvement was caused by the formation of carbonation products, such as hydromagnesite, nesquehonite, and lansfordite, and the constant high pH (~ 12) of the specimen, which favored the growth of hydration products such as calcium silicate hydrates and portlandite. Very low compressive strengths were found when 50 and 100% CO₂ atmospheres were used because of excessive formation of carbonation products, which occupied 78% of the specimen depth. Abundant carbonation products increased the specimen volume and decreased the pH to 10.2, slowing the growth of hydration products. The absence of brucite in specimens produced in a 100% CO₂ atmosphere indicated that MgO carbonation is favored over hydration at high CO₂ concentrations.