Abstract: Low carbon cementitious materials were prepared via carbonating magnesium slag mortars .The effects of water to cement ratio and carbonation curing duration on the compressive strength and microstructure of magnesium slag mortars were investigated .Results show that , the compressive strengths of mortars with a water to cement ratio of 0.4, after carbonation curing in CO 2 with a concentration of 99.9%and gas pressure of 0.1 MPa at 23 ℃ for 14 d, are increased by up to 9.9 times compared to those mortars without carbonation curing .The increase of carbonation curing duration increased the compressive strengths of the mortars .The influence of water to cement ratio on the strength of mortars was remarkable . The strength of specimens with lower water to cement ratio increased more after carbonation .According to microstructure analysis , it was found that the treatment of CO 2 enhanced the microstructures densification and decreased the amount of relatively coarse pores and total pore volume due to the formation of calcite ( CaCO 3 ) .

Key words: carbonation;magnesium slag;compressive strength;microstructure