Empa - Concrete & Asphalt - Hydration mechanism and properties of low-CO2 cements based on magnesium hydroxycarbonates

Hydration mechanism and properties of low-CO2 cements based on magnesium hydroxycarbonates

To lower CO2 emissions released from Portland cement manufacture, new cementitious materials (alternative binders), whose production are not as emission-intense as for Portland cement, became an active field of cement research in recent years. The aim of this project is to examine the suitability of MgO/hydromagnesite (Mg5(CO3)4(OH)2·4H2O) blends for construction purposes. These blends can potentially be used in concrete and display the possibility of a reduced CO2 footprint as a consequence of the manufacturing process of MgO. The process involves carbonation of magnesium silicate minerals such as forsterite (Mg2SiO4) or serpentine (Mg3Si2O5(OH)4) and subsequent calcination of the artificially obtained magnesite (MgCO3). The MgO/hydromagnesite binder remains a largely unexplored chemical system, which shall be investigated with chemical-analytical methods and finally be put into action by formulating concrete mix designs. The research is conducted at Empa by the Cement Chemistry and Thermodynamics group.

Project Period

2019 - 2023

100×25×25 mm3 mortar prism made of MgO/hydromagnesite blends following SN EN 196-1.

TGA of an unhydrated and a hydrated 70/30 wt% MgO/hydromagnesite paste after 6 h, 1 and 28 d of hydration. Phases present in sample: Brucite (Mg(OH)2), dolomite (CaMg(CO3)2), HY = hydromagnesite (Mg5(CO3)4(OH)2·4H2O), * = temperature range of an unidentified hydrate phase.

The addition of hydromagnesite to MgO is of great importance for hydration reaction acceleration and strength development in this type of binder. Thermogravimetric analysis (TGA) (Fig.2) and X-ray diffraction (XRD) (Fig.3) performed on MgO/hydromagnesite pastes indicated the presence of a hydrate phase, which might be related to strength development in MgO/HY binders in general, and is therefore, of interest for future studies.

Diffraction patterns of an unhydrated and hydrated 70/30 wt% MgO/hydromagnesite pastes after 6 h, 1, 2, 7, and 28 d of hydration. Main hydration products: Poorly-crystalline brucite (Mg(OH)2) (brc*) and a poorly-crystalline hydrate phase (art*). Unhydrated raw materials: Periclase (MgO) (per) and hydromagnesite (Mg5(CO3)4(OH)2·4H2O) (HY). Impurities from MgO raw material: Calcite (CaCO3) (cal), dolomite (CaMg(CO3)2) (dol), talc (Mg3Si4O10(OH)2) (tlc), phyllosilicate from the chlorite group (clc)

Team

Project Leader

Frank Winnefeld

Team

Alexander German

Pietro Lura

Publication

Winnefeld, F., Epifania, E., Montagnaro, F., and Gartner, E. M., 2019, "Further studies of the hydration of MgO-hydromagnesite blends", Cement and Concrete Research, 126, 105912

Conference Paper

Winnefeld, F., Epifania, E., Montagnaro, F., and Gartner, E. M., 2019, "Hydration of MgO in the presence of hydromagnesite", Proceedings of the International Conference on Sustainable Materials, Systems and Structures (SMSS 2019) - New Generation of Construction Materials, 20-22 March 2019, Rovinj, Croatia, Rilem Proceedings PRO 128, RILEM Publications S.A.R.L., Paris, France, 363-370

Winnefeld, F., Epifania, E., Montagnaro, F., and Gartner, E. M., 2019, "New insights into the hydration of cementitious materials based on magnesium carbonates", ILCCC 2019, 1st International conference on innovation in low-carbon cement & concrete technology, London, United Kingdom

A. German, F. Winnefeld, P. Lura, Hydratation von MgO/Hydromagnesit-Gemischen, Tagung Bauchemie, 54 (2019) Aachen, Germany, 151-157

German, F. Winnefeld, P. Lura, Hydratation of MgO/HY blends, ICCM, ACI/RILEM International Conference on cementitious materials and alternative binders for sustainable concrete, (2020) Toulouse, France. (accepted, conference postponed due to COVID-19)