Transforming industrial waste into valuable applications for concrete

Recycled concrete fines, mine tailings, steel slags, wood ash and many more – once carbonated in our Kalz reactors, they become supplementary cementitious materials (SCMs). These SCMs can replace clinker in the production process of cement, lowering emissions while turning concrete into a carbon sink. With over 4.1 billion tonnes of cement produced globally each year, and cement being responsible for up to 8% of global CO₂ emissions, the potential impact is significant.  

From some feedstocks that don’t make great SCMs, for example those with low reactivity, we can produce aggregates, which make up around 70-80% of concrete by weight. Conventional aggregates such as gravel could be replaced with our products that store CO₂. With an annual demand of 3 billion tonnes in Europe and 45 billion tonnes worldwide, aggregates represent one of the biggest opportunities for storing carbon dioxide in concrete applications.  

For some feedstocks, carbonation leads not to SCMs or aggregates, but to fillers, which improve the packing and workability of concrete. One of the most widely used fillers in concrete production is limestone powder. Especially when a carbonated material’s reactivity with cement is low or the feedstock material is only available regionally, fillers provide a practical use pathway. As inert components, they are easier to incorporate into concrete than active binders, while still contributing to performance through improved particle packing and workability. Globally, hundreds of millions of tonnes of fillers are used each year.