The characterization of magnesium binder: experimental approach to the study of the components

In this contribution an experimental approach aimed to characterized the binder produced by burning dolomitic rocks and some case studies will be presented. In our research a dolomitic stone composed by 31.5% of CaO and 23.5% of MgO2 and with low amounts of Al2O3, Fe2O3 and SiO2 (<1%) was burned at 950°C for one day. A quick lime composed by CaO and MgO was obtained. After slaking and curing of the binder for about 9 months in order to favour carbonation, the XRD (X ray diffraction), TGA (thermogravimetric) and FTIR (Infrared Spectrophotometry in Fourier Transform) analyses revealed an abundant amount of Ca(OH)2 (portlandite) and Mg(OH)2 (brucite) together with calcite. Despite the partial carbonation the physic and mechanical data of the material, showed the formation of a porous material with good mechanical resistance. The main problem in this experimental approach is the time of curing, which must be necessarily long because the introduction of any accelerating agent, such as a flow of CO2, can modify the reaction kinetic and also the stability of the carbonate phases such as amorphous carbonate and aragonite. Together with this experimentation, mortars from Tuscan historical sites, realized with a magnesian binder were studied with a mineralogical and petrographic approach using X-ray diffraction and optical and electronic microscopy. In particular the mineralogical and petrographic data acquired on binders and lumps of some Argentario Towers (XVI century) showed the relevant presence of brucite, hydromagnesite and calcite with traces of magnesite. The chemical analyses on electronic microscopy (SEM) evidenced an homogeneous distribution of Mg in the binders. In the case of the bedding mortars of Medieval site of Montarrenti (Siena), the binder was realized by burning dolomitic rock of the Montagnola Senese, and the only presence of hydromagnesite and calcite was evidenced. The formation of hydromagnesite and brucite inside the magnesium binder could to be responsible of good mechanical characteristics of the mortars.