Role of ammonium citrate in the preparation of high-strength carbonated steel slag cementitious materials

Abstract

Steel slag as a cementitious material exhibits enormous potential and feasibility through carbonation curing. In this study, the influences of Ammonium Citrate (AC) on the CO2 uptake, microstructure and properties of the carbonated steel slag cementitious materials were investigated from two perspectives: leaching of calcium and dissolution of CO2. The results showed that AC, as a pH regulator and chelating agent, can promote the leaching of calcium before carbonation and the dissolution of CO2 during carbonation curing. When the concentration of AC was within the range of 0–0.1 mol/L, the dissolved CO2 tended to react with Ca2+ and calcium citrate (AC-Ca) in steel slag samples, which increased the carbonation efficiency, and filling of pores by CaCO3 led to a rapid increase in the compressive strength. With the aid of AC, high-strength carbonated steel slag cementitious materials were prepared. Under optimal addition of AC (0.1 mol/L), CO2 uptake and compressive strength in carbonated steel slag cementitious materials with the densest pore structure reached 17.22 g/100 g steel slag and 99.2 MPa, respectively. However, with the overloading of AC (＞0.1 mol/L), the dissolved CO2 tended to react with C-S-H gels due to the high bonding strength between C5H7O5COO− and Ca2+, which accelerated the decalcification of C-S-H gels and divided the large pores into countless small pores in steel slag cementitious materials.