Expansive Calcium Sulfoaluminate Mortar for Extrusion of Chemically Prestressed Carbon Textile Reinforced Concrete

Abstract

In the precast industry, prestressing of reinforcement for extruded concrete elements is common. However, in the case of carbon textiles reinforcements, mechanical prestressing is technically complex, often leading to fiber damage or requiring specific equipment to prestress every single roving. Self‐prestressing, or chemical prestressing, offers a highly efficient and simple solution to address the aforementioned challenges. Additionally, it enables the possibility of prestressing structural elements with sophisticated geometries. Recent investigations have demonstrated the potential of using expansive calcium sulfoaluminate (CSA)‐based binders for the chemical prestressing of carbon textiles in casting. Nevertheless, the use of such mixtures for the extrusion of Carbon Textile Reinforced Concrete (CTRC) has not been explored yet. For defect‐free extrusion, additives like methylcellulose play a critical role in rheology modification, enhancing the mixture's consistency and thixotropy. Nonetheless, their interactions with the rapid hydration and expansion kinetics of CSA‐based binders are largely unknown. This study aims to develop a CSA‐based binder for the extrusion of CTRC. Extrudability parameters were assessed via sphere penetration and ultrasonic pulse velocity tests. Results demonstrated that a methylcellulose dosage of 0.75% provided a sufficient processing window, whereas 1.25% caused excessive stiffness and was unsuitable for extrusion. Additionally, the interaction between CSA phases and methylcellulose resulted in slower, broader hydration acceleration compared to an OPC reference. The extrudable OPC‐CSA mixture exhibited significant early‐age expansion of approximately 8.7 mm/m within three days. While this rapid expansion led to surface cracking, the incorporated fibers successfully bridged the cracks and maintained the overall integrity of the elements.