Effect of a high content in activated carbon waste on low clinker cement microstructure and properties

In the context of cement industry sustainability and socio-economic development, one of the primary objectives of the circular economy is the use of industrial waste as a supplementary cementitious material in the manufacture of future eco-efficient binders. This paper reports a first-time study of the effect of large proportions of the activated carbon (AC) waste used in low clinker cements on the properties and structure of the new binders. The behaviour of blended cement matrices prepared with 20%-50% AC as a pozzolan was analysed in terms of their chemical, mechanical and physical (rheology, heat of hydration, drying shrinkage, microporosity) properties. Macroporosity was also assessed with computed tomography (CT). The findings showed that these blended cements meet standard chemical and rheological requirements and that the 50% AC binder qualifies as a low heat cement. Drying shrinkage was observed to intensify with higher percentages of AC. A rise in total porosity was attendant upon pore size refinement, with an increase in the <100 nm fraction. Compressive strength declined with rising replacement ratios. Further to the CT findings, macroporosity (0.001-0.09 mm3) also increased with AC content, especially in the binders bearing 50% of the addition.