Development of a calcium sulfoaluminate-Portland cement binary system for twin-pipe 3D concrete printing

Recently, the twin-pipe pumping (TPP) system has been developed for 3D concrete printing which involves two mixtures, typically a Portland cement-based mixture and pure limestone powder-based that contains an accelerator. Following this, mixtures are allowed to be intermixed in static mixer placed just prior nozzle causes immediate stiffening very high buildability printed post-extrusion. However, flow division pattern produced by mixing baffles of results striations consisting unmixed powder resulting weak zones lower mechanical strength element. In this study, we present TPP borated calcium sulfoaluminate (CSA) mixture. The capable reacting independently with water as compared After getting blended right before extrusion, retardation CSA cement is destroyed alkaline component contained other stream, leading rapid hardening construction rate post extrusion from nozzle. hydration characteristics were studied using Vicat penetrometer, isothermal calorimetry, ultrasonic pulse velocimetry, while early age behavior was characterized uniaxial unconfined compression slow penetration tests. Results indicate alone cannot produce enough alkalinity destroy ulexite phase reinitiate cement, adding nominal dosage hydroxide can provide increase pH design suitable control. abundant would reduce at later ages due dilution effect, indicated P-wave velocity evolution yield stress evolution. addition, hardened elements performing flexural show CSA-Portland binary binder avoids formation hence improves behavior.