Effect of chelator on compressive strength and microstructure of CO2 curing cement paste

In this paper, chelator was used to accelerate CO2 mineralization curing cement paste. The mechanical properties and microstructure of CO2 curing cement paste with chelator were investigated through compressive strength test, low-field nuclear magnetic resonance (NMR) test, and scanning electron microscopy (SEM) observation. Next, the effect of chelator on the content of mineralized products was analyzed through X-Ray diffraction (XRD) test and thermogravimetric analysis (TGA). Finally, the CO2 absorption capacity of cement paste with chelator was evaluated through carbon sequestration rate calculation. The results showed that the chelator could improve the strength of CO2 curing cement paste and accelerate the mineralization reaction rate. With the increase of the chelator dosage, the compressive strength of cement paste presented a trend of first increasing and then decreasing. When the dosage of chelator was 0.5% of the cement content, the improvement effect on compressive strength of cement paste was the best, and under the premise of achieving equivalent mechanical properties, chelator could shorten the CO2 curing period of cement paste by half. NMR showed that chelator could promote the conversion of large pores to small pores in hardened cement paste. CO2 curing for 4 h, the porosity of pores above 40 nm in cement paste with 0.5% chelator decreased by 17.0% compared to ordinary cement paste. Based on the XRD and TGA on the mineralization reaction zone, it was found that the addition of 0.5% chelator could improve the CO2 curing degree of cement paste. CO2 curing for 48 h, the 0.5% chelator could effectively increase the yield of mineralized product CaCO3 by 22.5%. CO2 curing for 4 h and 48 h, the cement paste with 0.5% chelator could increase the carbon sequestration rate by 11.8% and 17.4% compared with ordinary cement paste, respectively.