Substrates / starting materials
Mg(OH)2 (brucite, labelled MH)

Modifiers:
Magnesium acetate, Mg-acetate
Ammonium acetate, NH 4-acetate
Glycine
Deionized water
CO2 gas (10% CO2 , 80±5% RH, 23±1℃)

Reaction conditions

Modification:
1 mol/L acetate ions in 500 mL deionized water
29 g Mg(OH)2
Ultrasonic dispersion for 3 min
Stirring at 500 rpm for 2 hCentrifugation, vacuum filtration, washing with DI water three times
Drying at 80 ℃ for 24 h
Modification repeated 5 times to test modifier recycling

Paste preparation:
Modified or unmodified Mg(OH)2 mixed with water
Water-to-binder ratio: 0.68
Cast into 20×20×20 mm³ cubes
Demoulded after 24 h

Carbonation curing:
23±1℃, 80±5% RH, 10% CO2
​Up to 28 days

Products
Modified Mg(OH)2:
MH-M: Mg(OH)2 modified by Mg-acetate
MH-N: Mg(OH)2 modified by NH4-acetate
MH-G: Mg(OH) 2 modified by glycine MH-M-R5, MH-N-R5, MH-G-R5: modified Mg(OH) 2 after 5 modifier recycling cycles

Carbonation products:
Unmodified Mg(OH)2 pastes: mainly nesquehonite, Mg(HCO3)(OH)⋅2H2O Modified Mg(OH)2 pastes: hydromagnesite/dypingite-like phases, including hydromagnesite Mg5(CO3)4(OH)2⋅5H2O, dypingite Mg5(CO3)4(OH)2⋅4H2O, and girogiosite Mg5 (CO3 ) 4 (OH)2⋅5−6H2O
Residual unreacted brucite, Mg(OH) 2