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Abstract

Abstract Controlling the structural build-up in fresh cementitious composites is crucial for 3D printing. This study revealed that continuous shearing can be an effective tool for controlling the structural build-up in fresh cementitious pastes. The tool's sensitivity to the water‑to‑binder ratio and Class C fly ash (FAC) was also examined. Using a rheometer, the structural build-up evolution was obtained by measuring the static yield stress (τ sy ) at 10-min intervals until the paste reached a rigid τ sy threshold. Two binder systems were tested at w/b of 0.40 and 0.48: (i) 100% Limestone Portland Cement (PLC) as the binder, and (ii) a blended system with PLC (80%) + FAC (20%). Each mixture was assessed under static (no external agitation) and dynamic (continuous shearing at rest) conditions. Results indicate that, regardless of the mixture, it is possible to significantly alter the structural build-up and the physical setting time based on the rheological behavior. For both binder systems, increasing the w/b ratio made the paste more responsive to dynamic conditions, resulting in further delayed structural build-up. Additionally, the use of fly ash enhances the ability to control structural build-up and setting time through continuous shearing. Therefore, increasing the water-to-binder ratio and incorporating fly ash extends the options for manipulating the structural build-up and setting time via external shearing. These findings emphasize the potential of pre-placement external continuous shearing as an active tool to regulate structural build-up in real time, especially for 3D printing, as it alters rheological behavior without altering the mix design.