Performance and microstructure of calcined dolomite and reactive magnesia-based concrete samples

This study investigates the performance and microstructural development of reactive MgO and calcined dolomite-based concrete samples subjected to carbonation curing for up to 28 days. The performance of each sample is assessed via compressive strength testing, which is linked with the hydration and carbonation mechanisms studied via isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis with differential scanning calorimetry (TGA/DSC), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX). Strength gain depends on the carbonation degree and morphology of carbonate phases such as hydromagnesite and nesquehonite, whose formation is controlled by the binder composition and initial porosity of each sample. Higher contents of MgO enable early strength gain, whereas the presence of undecomposed carbonate phases in dolomite facilitates the continuation of the hydration and carbonation reactions by providing additional nucleation sites and contributing to the formation of a dense carbonate network. Continuous strength gain is achieved by the extensive formation of a carbonate network. Simultaneous use of MgO and dolomite enables 28-day strengths as high as 57 MPa, which are up to 60% higher than that of the control samples containing only MgO or dolomite.