Ultra-green construction: reactive magnesia masonry products

As worldwide production of Portland cement (PC) is one of the major contributors to global anthropogenic carbon dioxide emissions, a range of carbon-reduction initiatives are being considered. One recent development, namely reactive magnesia cements, has received significant attention as a promising sustainable alternative to PC. Reactive magnesia cements are blends of PC and reactive magnesia in different proportions depending on the intended application, from high-density concrete to porous masonry units. An extensive investigation into the strength development of reactive magnesia cement masonry units, in which the PC is either partially or completely replaced by reactive magnesia, has been carried out. The results show that when subjected to accelerated carbonation conditions, such units can achieve strengths that far exceed those of corresponding PC blocks – both in laboratory studies and full-scale commercial trials. In order to determine their environmental advantages, quantification of carbon dioxide sequestration during carbonation of these blocks was performed using X-ray diffraction. This paper presents an overview of the strength performance of reactive magnesia cements in masonry blocks and links that to microstructural analyses using X-ray diffraction and scanning electron microscopy. The paper also presents a quantification of the degree of hydration and carbonation within the blocks. The results are compared with corresponding PC and lime systems.