Mechanical and microstructural changes in reactive magnesium oxide cement-based concrete mixes subjected to high temperatures

This study investigated the mechanical, microstructural, and chemical changes in reactive MgO cement-based concrete cured under ambient and accelerated carbonation conditions, followed by exposure to high temperatures. The compressive strength of the ambient-cured samples increased from 10 to 30 MPa when subjected to up to 200 °C, induced by increased hydration of the remaining MgO. The accelerated formation of brucite at 50 °C also enhanced the compressive strength of the carbonated samples (58 vs. 65 MPa). A relatively stable performance (~56 MPa) was observed at temperatures ranging between 100 and 300 °C for the carbonated samples, associated with additional formation of brucite and transition of nesquehonite and hydromagnesite to artinite. The hydrated magnesium carbonates (HMCs) forming around brucite acted as barriers and delayed its dehydroxylation. The decomposition of brucite and HMCs at 400 °C caused a porous microstructure and a low residual strength (5–8 MPa) in both the ambient-cured and carbonated samples.