Tailoring rheology and mechanical properties of 3D printed mortars with nanoclays and superplasticizer

Extrusion-based 3D concrete printing (3DCP) is emerging as a viable construction method due to its potential to enhance automation, reduce material waste and enable low-carbon construction solutions. However, its practical implementation remains constrained by the need for precise control of fresh-state rheology and early-age structural stability. This study investigates the combined influence of three nanoclays, attapulgite (ATT), bentonite (BEN) and sepiolite (SEP), together with a polycarboxylate ether superplasticizer (SP) on the rheological and mechanical behaviour of sustainable mortars developed for 3DCP-related applications. The binder system incorporates 50 % ground granulated blast furnace slag (GGBS) and 3 % silica fume (SF) to reduce embodied carbon while maintaining performance. A controlled shear-rate protocol was used to quantify static yield stress, dynamic yield stress, thixotropy and plastic viscosity, supported by slump-flow and compressive and flexural strength testing at 7 and 28 days. The results show that all nanoclays significantly enhance structuration and thixotropy, with SEP producing the strongest increase in static yield stress and structural rebuilding. ATT and BEN also improved rheological stability, although with lower intensity. SP dosage strongly governed flow behaviour, with 1 % providing the most favourable balance between flowability and shape stability. Nanoclay-modified mixes exhibited reduced slump flow and increased plastic viscosity relative to the reference. SEP yielded the highest 28-day compressive strength, while flexural strength decreased slightly across all nanoclays. The findings demonstrate that targeted combinations of nanoclay and SP can effectively tailor the rheology of low-carbon mortars, indicating their potential suitability for 3D concrete printing.