Activated Calcined clay limestone cements and their potential for automated manufacturing of folded carbon‐reinforced concrete shell structures

Abstract

Automated production of carbon‐reinforced concrete is a sustainable approach towards complex prefabricated structures. A promising approach combines extrusion and subsequent folding to create lightweight shell elements. This process requires stiff, highly thixotropic mortars with binder contents up to 700 kg/m ³ . The present work focuses on optimizing a mortar composition and developing low‐clinker binders for this two‐step manufacturing route using calcined clay limestone cements (LC ³ ). LC ³ ‐40 systems are investigated for normal‐strength mortars, respectively. Two calcined clays, a kaolinite‐rich one ∼60 wt.% kaolinite) and a medium‐grade clay containing illite (∼20 wt.%) and kaolinite (∼40 wt.%) are investigated. A major challenge for low‐clinker binders in extrusion‐based prefabrication is achieving sufficient strength within 24h. To address this, a two‐component activator consisting of Na ₂ SO ₄ and sodium gluconate is used to accelerate hydration and tailor structural build‐up while avoiding adverse effects of high alkali contents on later‐age strength. The results presented here confirm the validity of this approach on LC ³ binders, while being a proof of concept for this manufacturing route.