Impact of amino acids as performance-controlling additives on the hydration of reactive MgO

Abstract

© Copyright 2022 The Author(s). Since reactive magnesia (MgO) is produced at a lower temperature than CaO and is capable of sequestering significant quantities of CO2, it is considered to be a technically superior and more sustainable alternative to Portland cement. To obtain maximum carbonation and associated high strength, a variety of additives are investigated for MgO. Using amino acids as an additive is a new concept to control the polymorphism of carbonates. As the hydration of magnesia plays an important role in magnesia carbonation, this study investigates the impact of amino acids (i.e. L-arginine (L-Arg) and L-aspartic (L-Asp)) on the hydration of magnesia. Subsequent tests, including X-ray diffraction (XRD), pH tests, inductively coupled plasma optical emission spectrometry (ICP-OES), thermogravimetry (TG) - differential thermogravimetry (DTG), and scanning electron microscopy-Energy-dispersive X-ray spectroscopy (SEM-EDX) were conducted after the measurement of their strength development. The results revealed that magnesia hydrated with/without amino acids only formed brucite (Mg(OH)2) as the hydration product. A lower hydration degree was observed in the hydrated composites with the presence of amino acids, regardless of the type of amino acids. Specifically, the use of L-Asp not only delayed the hydration of MgO but also reduced the amount of brucite. The increasing amorphousness of brucite with increasing L-Asp concentration was also observed, compared to the control batch. Additionally, Mg2+ concentration was increased with the addition of L-Asp, allowing the blends to absorb more CO2 with a higher concentration of Mg2+.