Low‐CO₂ cements based on magnesium oxide / hydromagnesite blends – hydration mechanism and mechanical properties

Abstract

Binders based on blends of reactive magnesia and hydromagnesite are low‐CO2 or even carbon‐negative cements in case the MgO is generated from magnesium silicates or Mg‐containing brines. When MgO is hydrated with water alone, a well crystalline brucite forms, but no measurable strength is developing. In the presence of hydromagnesite, the hydration of MgO is accelerated and the hydrate assemblage is changed. A poorly‐crystalline brucite containing some carbonate is the main hydration product. Furthermore, a kind of “gel‐water” is observed, which is lost at temperatures above 40‐60°C. This brucite‐like phase is responsible for strength formation in MgO‐hydromagnesite blends. After 28 days, a mortar compressive strength is reached similar to the one of a Portland cement of strength class 32.5.