The effect of restrained early age shrinkage on the interlayer bond and durability of 3D printed concrete

3D printed concrete exhibits a high magnitude and rate of plastic shrinkage (early age drying-induced shrinkage) compared to conventional cast concrete. This study investigated if restraining this shrinkage adversely affects the long-term durability and mechanical performance. Shrinkage was restrained by inserting reinforcement-like rods into the fresh concrete and exposing the specimen to a moderate evaporation rate. The interlayer bond strength, permeability and ion penetration of the unrestrained and restrained specimens were then compared. The results show that shrinkage causes shear strain concentrations at the interlayers due to a lack of particle interlocking and non-uniform pore water evaporation from the undulated evaporation face. Consequently, discrepancies in the transfer of shrinkage between layers occur, a phenomenon coined as interlayer slip. Evidence is presented of a 12% reduction in interlayer bond strength, a 70% higher permeability and 17% higher chloride ion penetration. These adverse consequences were due to interlayer slip and microcracking. Nonetheless, the durability of uncracked printed concrete is satisfactory, even with localised interlayer slip and microcracking. [Display omitted] •Early age shrinkage can cause shear strain concentrations at the interlayers of 3DPC.•Interlayer slip occurs due to non-uniform pore water evaporation and lack of particle interlocking at the interlayer region.•When shrinkage was restrained, the interlayer bond strength decreased, and the permeability and ion penetration increased.•The adverse consequences of restrained shrinkage are mostly attributed to microcracking and not solely to interlayer slip.