Influence of effective microorganisms on the rheology and fresh state properties of SCMs-based concrete for digital fabrication

Abstract

A reduction in the cost and anthropogenic CO2 emissions of Portland cement production can be achieved by adding supplementary cementitious materials (SCMs) obtained from industrial origins, like fly ash, silica fume, slagments, and naturally available such as limestone and kaolinitic clay. Replacement of large quantities of cement with SCMs profoundly influences the fresh and mechanical characteristics of structural concrete. This study presents an experimental investigation to evaluate the influence of effective microorganisms (EM) on freshly mixed fly ash- and limestone calcined clay (LC2) cement-based fibre-reinforced printable concrete (FRPC). EM is a mixture of three different microorganisms: photosynthetic bacteria, lactic acid bacteria, and yeast. Its inclusion complements green concrete and is environmentally friendly for a sustainable environment. Four mixes (i.e., fly ash cement-based mix, LC2 cement-based mix, and both mixes induced by EM) were prepared and examined to achieve printable concrete of varying rheological properties, and tested for slump and slump flow, setting/open time, rheological characterisation of various parameters, and buildability performance. The findings from this study revealed that the SCMs and the EM considered exhibited satisfactory material rheological performance and other unique characteristics identified as critical early-age properties for suitable 3D printability. In addition, near zero slumps were displayed for all the mixes and the slump flows were in the range of 140 – 160 mm after standard small slump flow table impact agitation, implying remarkable and adequate results for printable concrete. The penetration, bleeding, and segregation was also reduced when compared with no SCM inclusion. Conclusively, good relationships between the fresh properties and buildability quantification are also presented.