Interlayer Bond and Porosity of 3D Printed Concrete

Abstract

Extrusion-based concrete 3D printing is being increasingly investigated for its application in the construction industry. Having a layer-wise extrusion process could impart a lack of fusion between the layers due to drying and moisture migration between the layers, resulting in higher porosity and weak interlayer bond strength. This paper presents a study to understand the effect of fresh cement paste applied in between the two layers on the porosity and bond behaviour of samples printed at a relatively high interlayer time gap of 15 min. Two different types of 3D printable mixtures were considered in this study: (i) a Portland cement-slag binary blend mixture and (ii) a calcium sulfoaluminate cement-based mixture. Two-layered wall elements were printed with a constant 15 min interlayer time interval. The interlayer bond strength was determined by pull-off tests and compared among the different mixtures with and without a Portland cement-based paste applied between the layers. Also, the porosity of the printed elements was studied with mercury intrusion porosimetry. The results indicate that the total porosity and critical pore diameter decrease with the application of the fresh cement paste. Also, the bond strength increases slightly with the application of cement paste as it reduces the total porosity of the samples.