Accelerated carbonation – A potential approach to sequester CO2 in cement paste containing slag and reactive MgO

Reply to the discussion of the papers “ Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements ” and “ Enhancing the carbonation of MgO cement porous blocks through improved curing conditions ”, by S.A. Walling and J.L. Provis

“…We have also clearly stated the difficulty in: (i) evaluating the final stoichiometry of the carbonated phases due to a series of overlapping decompositions in DTA profiles, and (ii) preparing a sample truly representative of the actual block due to the high aggregate content used in the original mix composition that was hard to break into powder form in preparation for thermal analysis. Some of these concerns were expressed in studies performed by other researchers as well [7]. Our comments in our two papers evidently highlight the possibility of the powder containing more than the originally included 10% cement, which would result in the overestimation of the amount of water and CO 2 within the mixes calculated by the results obtained from the TGA.…”

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 .…”

“…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 . Therefore, accelerated carbonation with an elevated CO 2 concentration (>50%) is usually employed as the curing technique for paste, mortar, or concrete containing r‐MgO to enhance the mechanical properties .…”

Properties of Cement Paste Containing High Volume γ-C2S and MgO Subjected to CO2Curing

“…현재까지의 기존문헌들은 CO 2 양생에 관 한 초기 연구 단계로써 보통포틀랜드시멘트에 국한되어 있 으며 압축강도 증가율에 초점이 맞추어져 있다 [6,7]. 또한, 최근 대표적으로 사용되고 있는 혼화재 혼입 콘크리트의 CO 2 양생 결과 외에 [8] γ-C 2 S와 MgO와 같은 CO 2 양생 의 효과를 크게 발휘할 수 있는 CO 2 흡수물질을 혼입한 콘 크리트의 CO 2 양생에 따른 압축강도 발현 효과에 관한 연 구가 진행되었으나 CO 2 흡수물질 혼입율이 낮은 경우의 결 과만 발표된 실정이다 [6,9,10,11,12,13].…”