Bio-Based Additives to Improve the Rheology of High-Volume Fly Ash Cement-Based Mortar for 3D-Printing

The developments in digital concrete production placed the concrete industry in a paradox regarding achieving optimization among improved performance, cost, and sustainability. While high performance in three-dimensional (3D)-printed structures requires more cement-based material in the mix, it contradicts the sustainability goal of reducing the total volume of cement production. This study aims to develop a novel mix design approach using bacterial cells as a rheology modifier for high-volume fly ash (HVFA) mortars. The mix design composition used in this study includes 70% fly ash and 5% slaked lime by the weight of the binder as a filler. Bacterial cells were added to mix water with sepiolite clay. Herein, the bacteria-sepiolite component was referred to as a bio-based additive and introduced to the mix by 2% and 4% of the binder weight. The rheological performance was assessed by controlled shear rate and static yield stress tests. The results showed that incorporating bacterial cells increased the time-dependent evolution of static yield stress and resulted in a higher degree of thixotropy. The designed bio-based additive improved the rheological properties, which can provide the required printability parameters for HVFA mortars.