Fresh and Hardened Properties of 3D-Printed Concrete Made with Dune Sand

This paper examines the performance of 3D-printed concrete made with locally abundant desert dune sand. Cement was replaced by up to 10% silica fume and 30% fly ash to reduce its detrimental environmental footprint. The water-to-binder ratio used in the mix ranged between 0.35 and 0.40. Also, a superplasticizer was added in the range of 1 to 3%, by binder mass. Concrete mixes were proportioned to attain optimum fresh and hardened properties. A control mix with crushed dolomitic limestone aggregates served as a reference. The performance of 3D-printed concrete mixes was assessed based on slump flow, pumpability, and compressive strength. Experimental results showed a reduction in slump flow and pumpability with an increase in dune sand content. In turn, the compressive strength increased by 3% when 20% dune sand was utilized, but decreased by an average of 3% for every additional 10% subsequently. Concrete mixes incorporating a superplasticizer and higher water-to-binder ratio exhibited improved workability. While the former caused limited change to compressive strength, the latter resulted in a notable decrease. Upon replacing cement with silica fume and fly ash, the slump flow and pumpability increased. In fact, 3D-printed concrete made with 3% superplasticizer, 20% fly ash, and 10% silica fume experienced a 230 and 79% increase in slump flow and pumpability, respectively. Compressive strength increased by an average of 4% for every 10% fly ash replacement. The incorporation of 10% silica fume improved the strength by an additional 14%. Analytical models were developed to correlate slump flow to pumpability and 3D-printed concrete compressive strength to that of typical concrete cubes, serving as guidelines to produce optimal concrete mixes for large-scale concrete 3D printers.