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

This study investigated the mechanical and microstructural changes in reactive MgO cement-based concrete cured under ambient and accelerated carbonation conditions, followed by exposure to high temperatures. The compressive strength of ambient-cured samples increased from 10 to 30 MPa when subjected to up to 200 °C, which was achieved via increased hydration of the remaining MgO. The accelerated formation of brucite at 50 °C enhanced the compressive strength of 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 the additional formation of brucite and the transition of nesquehonite and hydromagnesite to artinite. The hydrated magnesium carbonates (HMCs) forming around brucite acted as barriers and inhibited 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.