Qualitative assessment of interfacial bonding in 3D printing concrete exposed to frost attack
Joseph J. Assaad, Farook Hamzeh, Bilal S. Hamad
Abstract
The 3D printing technology is a novel construction process to build concrete structures layer-by-layer based on computer digital programs. The main objective of this research program is to develop a testing protocol that replicates the successive placement of mortar layers and satisfactorily measures the effect of repeated freeze/thaw (F/T) cycles on durability and interfacial bond strengths. Three mortar series made with different binder and mixing water contents are tested; the consistency of mixtures was adjusted to allow proper extrusion using a laboratory 3D printer. Particular emphasis was placed to compare the efficiency of air-entraining agent (AEA) and styrene-butadiene rubber (SBR) latexes to protect mortars against deterioration due to frost attack. The incorporation of SBR was found more efficient than AEA to mitigate the drop in bond strength due to F/T cycles, given the enhanced flexibility of the polymer-modified mortars that accommodate the deformations and stresses created along the interfaces. The pull-off test results obtained were successfully validated using specimens generated from the laboratory 3D printer.