Fired clay-based construction and demolition waste as pozzolanic addition in cements. Design of new eco-efficient cements

Abstract

Industrial waste and by-products are being widely used by the cement industry to enhance process efficiency and sustainability, in keeping with EU circular economy guidelines. This study assessed the properties of newly designed cements bearing fired clay-based C&DW against European standards. The findings showed that the blended cements met all the chemical, physical and mechanical requirements presently in place. They were also observed to qualify as type II and type IV cements, inasmuch as they contained waste that reacted with the calcium hydroxide released during cement hydration to generate the respective products. In addition, the inclusion of 10% or 20% C&DW yielded cements that could be classified as European standard strength classes 42.5 and 52.5. With a 30% C&DW, the resulting binder was a low heat of hydration cement. The present research confirmed the pozzolanic behaviour of waste in cement/C&DW systems, attested to by the reduction in both pore size and portlandite content. The new hydration products forming as a result of the pozzolanic reaction enhanced the flexibility and plasticity of the mortars prepared with the new cements relative to the mortars bearing unadditioned cement.