Maciej Zajac is a principal scientist in the Global Research and Development Department of HeidelbergCement, one of the largest building materials companies in the world headquartered in Heidelberg, Germany. He leads research efforts to develop innovative and sustainable products as a contribution to climate protection and to generate added value for customers and the company. Maciej Zajac received his PhD in Physical Chemistry at Burgundy University (Dijon, France) in 2007 and then moved to HeidelbergCement as a junior scientist. As a principal scientist Maciej supports and leads multiple key R&D projects including the collaboration with the external partners. His current research focuses on circular economy and CO2 utilization by mineral carbonation in construction industry.
Mechanisms of CO2 mineralization by cementitious materials and of their reactivity in new cement formulations
Production of Portland clinker is inherently associated with CO2 emissions originating from calcination of limestone, the irreplaceable large-scale source of calcium needed in the cement binder. CO2 mineralization of clinkers, end-of-life concrete, and similar mineral systems can provide an important reduction in the overall process of CO2 emissions associated with cement production, which seems much more attractive than carbon capture and storage. CO2 mineralization of cement materials utilizes that calcium reacts with carbonate ions in an exothermic process, forming calcium carbonate where CO2 is bound on a geological scale. Recent research has shown that this approach can be applied in several environmentally and economically favorable ways at different stages of the concrete life cycle by carbonation of either clinkers or hydrated cement phases. This contribution focussed on the application of carbonation technologies to valorize the industrial streams of cement-based materials. Different approaches and technologies for cement carbonation will be discussed along with the associated reaction mechanisms for the relevant phase assemblages. Furthermore, reactivity and application of the carbonated materials as the pozzolanic additive for the cement and concrete production will be addressed. Recent results demonstrate that carbonation of different industrial material streams can be conducted at ambient temperature and pressure, achieving high degrees of reaction in contrast to the current level of carbonation of natural magnesium silicate rocks. Carbonation, when combined with recycling approaches, can make an important contribution to the circularity of the process of CO2 emissions from clinker production and a significant reduction in the CO2 footprint of cementitious materials.