Eco-Friendly, Set-on-Demand Digital Concrete

Digital fabrication with concrete is considered to potentially revolutionize the construction sector and is often presented as a means to reduce its environmental footprint. However, at least in the case of concrete, it encounters significant challenges in terms of material design, since high paste volumes and Portland cement contents are normally used due to process requirements. In this article, the application to layered extrusion of a recently developed low clinker cement containing 50% Portland cement and 50% supplementary cementitious materials, such as limestone, burnt oil shale, and fly ash, is presented. It is found that an accelerator paste composed by Calcium Aluminate Cement (CAC) and anhydrite provides the required hydration and structural build-up for 3D printing, while not compromising the early and long-term compressive strength. Such a low clinker mortar can be successfully retarded, processed, pumped, and extruded just after mixing it in line with the accelerator paste. This accelerated mortar formulation contains only 303 kg/m(3) of Portland cement, which is roughly half the amount used in current accelerated formulations used for digital fabrication with concrete.