Optimising limestone calcined clay cement containing excavated low-grade waste clay for 3D printing applications

Abstract

Recent studies reported the use of limestone calcined clay cement (LC3) as a low-carbon binder for 3D concrete printing (3DCP) applications. These studies typically used 1:1 clay minerals, specifically medium to high-purity clays, containing a minimum of 40 % Kaolinite. This study aims to valorise low-grade waste clay (representative of 2:1 clay mineral with a maximum of 20 % Kaolinite content) excavated from a tunnelling project to develop an LC3 mixture for 3DCP applications. This research investigates the effect of different calcination temperatures, dosages of superplasticiser (SP) and viscosity modifying agent (VMA) on the fresh properties, mechanical characteristics, reaction kinetics, shape stability, and buildability of the developed mixes. The results revealed that activating excavated clay at 800 °C exhibited the highest reactivity compared to calcination temperatures of 700 and 900 °C. The incorporation of admixtures (i.e., SP and VMA) had varying effects on the fresh and mechanical properties of the mixtures. The LC3 mixture containing 1 wt% SP and 0.6 wt% VMA (by weight of the binder) exhibited robust shape stability and achieved the best mechanical performance among the mixtures investigated in this study and had an open time of 65 min. A cylindrical object was successfully printed using this mixture, confirming its suitability for 3DCP applications. Environmental impact calculations showed that replacing OPC with the developed LC3 mixture provides significant environmental benefits, reducing CO2 emissions by around 39 %. This study confirms the feasibility of using excavated low-grade waste clay as feedstock for 3DCP applications.