Ceramics-Silikáty

Sustainable ultra-high-performance concrete (UHPC) is an advanced cementitious composite known for its exceptional strength, ductility, and durability. However, its high cement content contributes significantly to the carbon footprint, and the addition of cementitious materials is recommended to address this. In this regard, research on metakaolin, a natural pozzolan, is important. However, metakaolin has been mainly used in combination with silica fume or with silica fume and other pozzolans like fly ash and slag. Studies on binary compositions of UHPCs with metakaolin are scarce in the literature. In the present study, compositions with varying cement contents, containing 15-25% metakaolin, were investigated. The study also considered two other natural materials with some pozzolanic reactivity, zeolite and limestone powder, to understand their effectiveness. These mixtures are compared to pozzolan-free compositions and a conventional composition containing only silica fume. The main evaluations of the study focus on the mechanical strength performance, permeability properties, such as water absorption, pore permeability, sorptivity, acid resistance, chloride penetration, and carbonation. In addition, factors, such as the GWP, carbon footprint and cost, were analysed to assess the environmental sustainability of UHPFRC compositions incorporating metakaolin.