Effect of Fly Ash, Basalt Fiber and Attapulgite Nanoclay on the Fresh Properties, Rheology and Shrinkage Behaviour of Printable Concrete (2026-01)¶

The application of 3D concrete printing (3DCP) has attracted significant attention in the construction sector for its potential to revolutionize building processes. Unlike traditional methods, 3D printing eliminates the need for formwork, but it requires concrete mixtures with specific rheological properties to enable smooth extrusion and shape retention after printing. This study delves into the formulation of a unique blend of Portland Cement with fly ash, basalt fibre, and attapulgite nanoclay (nC) specifically tailored for 3D printing applications. This study provides new insights into the early-stage hydration kinetics and microstructural intricacies of these mixtures using techniques like X-ray diffraction and thermogravimetric analysis. This research investigates the influence of nanoclay on key properties such as initial rheological properties, structural build-up rate, setting time, the printing speed of 3D printable concrete and shrinkage properties. Microstructural analyses like XRD and TGA were conducted on a ternary system of fly ash, cement, and nanoclay, to interpret the mechanisms underlying early strength development. Standardized field-friendly testing methodologies have been adapted to suit printable concrete for 3D printing, and a framework has been introduced to gauge the rate of structural build-up using tests like cone penetration and scissometer tests. Within the scope of this study, a new cyclic unconfined uniaxial compressive testing (UUCT) process has been introduced as a tool for ascertaining the printing speed in 3DCP applications. The effects of nanoclay and basalt fibre on shrinkage properties of printed specimens, from initial plastic shrinkage to drying shrinkage over a span of 90 days, have been examined, an aspect not discussed in existing literature. The research findings highlight that incorporating up to 6 kg/m3 of nanoclay and about 2.1 kg/m3 of basalt fibre to the mix, the structural build-up rate is enhanced, permitting faster concrete printing, and reducing shrinkage post printing process.