Characterization of Mg components in reactive MgO – Portland cement blends during hydration and carbonation

Design of carbonated r‐MgO‐PC binder system: Effect of r‐MgO replacement level and water‐to‐binder ratio

“…Compared to the 20%‐0.55 and 20%‐0.50 mortars, the XRD pattern of the 20%‐0.45 mortar exhibits lower intensities corresponding to portlandite and greater intensities corresponding to Mg‐calcite, which agrees with the greatest carbonation front of the 20%‐0.45 mortar among the three mortars in Figure . The reaction mainly involves the carbonation of Mg 2+ and Ca 2+ forming Mg‐calcite . In terms of the thermal decomposition, M–S–H experiences a similar process as calcium silicate hydrate (C–S–H), which continues to a major mass loss at the temperature range of 50°C‐300°C .…”

“…Nevertheless, the thermal decomposition of the residual M–S–H and C–S–H mainly contributes to the mass loss at the temperature range of 50°C‐300°C, corresponding to their dehydration process. Other than that, the character of TGA curves in Figure includes: (a) the mass loss and DTG peak at the temperature range of 50°C‐300°C are due to the dehydration of nesquehonite and the hydrated amorphous Mg carbonate; (b) the mass loss and DTG peak at the temperature range of 300°C‐480°C are due to the composition of brucite, nesquehonite, and the hydrated amorphous Mg carbonate; (c) the mass loss and DTG peak at the temperature range of 480°C‐650°C are due to the second step decarbonization of nesquehonite; and (d) the mass loss and DTG peak at the temperature range of 650°C‐950°C are due to the decomposition of Mg‐calcite. The TG curves of the 60%‐0.70 and 60%‐0.65 mortars yield similar mass losses at the aforementioned four temperature ranges, which manifests a comparable degree of carbonation.…”

“…According to the stoichiometric calculation in Ref. [2], the water demand for the hydration of 100 g r‐MgO and 100 g PC are 39.8 and 20.9 g, respectively, based on the chemical composition of r‐MgO and PC in Table . (b) A higher w/b ratio of r‐MgO‐PC systems results in a greater initial pore volume and greater moisture evaporation during the drying process, compared to mixes with lower w/b ratios .…”

“…The study of reactive MgO (r‐MgO) as a replacement of Portland cement (PC) stems from a potential environmental‐friendly method to manufacture an MgO product with a high reactivity . The hydration of a binder system consisting of r‐MgO and PC (r‐MgO‐PC) yields brucite, magnesium silicate hydrate (M–S–H) and hydrotalcite‐like Mg–Al layered double hydroxides in addition to the conventional hydration products of PC . However, the hydration product of r‐MgO is found to make a minimal contribution to the compressive strength of the matrix .…”

“…A relative humidity greater than 75% and a CO 2 concentration greater than 50% have already been identified to benefit the carbonation degree of an r‐MgO‐PC system . The r‐MgO replacement level, namely the mass ratio of r‐MgO/(r‐MgO + PC) in the binder system, determines the type and quantity of carbonation products of an r‐MgO‐PC system . Mo and Panesar cast paste and mortar specimens with a constant w/b ratio of 0.5 and various r‐MgO replacement levels from 0% to 40%.…”